DP8421AVX-20_技术文档

July 1992

DP8420A/21A/22A microCMOS Programmable

256k/1M/4M Dynamic RAM Controller/Drivers

General Description

Features

Y

On chip high precision delay line to guarantee critical

DRAM access timing parameters

The DP8420A/21A/22A dynamic RAM controllers provide a

low cost, single chip interface between dynamic RAM and

all 8-, 16- and 32-bit systems. The DP8420A/21A/22A gen-

erate all the required access control signal timing for

DRAMs. An on-chip refresh request clock is used to auto-

matically refresh the DRAM array. Refreshes and accesses

are arbitrated on chip. If necessary, a WAIT or DTACK out-

put inserts wait states into system access cycles, including

burst mode accesses. RAS low time during refreshes and

RAS precharge time after refreshes and back to back ac-

cesses are guaranteed through the insertion of wait states.

Separate on-chip precharge counters for each RAS output

can be used for memory interleaving to avoid delayed back

to back accesses because of precharge. An additional fea-

ture of the DP8422A is two access ports to simplify dual

accessing. Arbitration among these ports and refresh is

done on chip.

Y

microCMOS process for low power

High capacitance drivers for RAS, CAS, WE and DRAM

address on chip

Y

On chip support for nibble, page and static column

DRAMs

Byte enable signals on chip allow byte writing in a word

size up to 32 bits with no external logic

Selection of controller speeds: 20 MHz and 25 MHz

On board Port A/Port B (DP8422A only)/refresh arbitra-

tion logic

Y

Direct interface to all major microprocessors (applica-

tion notes available)

4 RAS and 4 CAS drivers (the RAS and CAS configura-

tion is programmable)

Largest

DRAM

Direct Drive

Memory

Access

Ports

Ý

of Pins

of Address

Outputs

Control

(PLCC)

Possible

Capacity

Available

DP8420A

DP8421A

DP8422A

68

84

9

256 kbit

1 Mbit

4 Mbit

4 Mbytes

16 Mbytes

64 Mbytes

Single Access Port

10

11

Single Access Port

Dual Access Ports (A and B)

Block Diagram

DP8420A/21A/22A DRAM Controller

TL/F/8588–5

FIGURE 1

TRI-STATEÉ is a registered trademark of National Semiconductor Corporation.

Staggered Refresh^TMis a trademark of National Semiconductor Corporation.

C

1995 National Semiconductor Corporation

TL/F/8588

RRD-B30M105/Printed in U. S. A.

Table of Contents

1.0 INTRODUCTION

6.0 PORT A WAIT STATE SUPPORT

6.1 WAIT Type Output

2.0 SIGNAL DESCRIPTIONS

2.1 Address, R/W and Programming Signals

2.2 DRAM Control Signals

6.2 DTACK Type Output

6.3 Dynamically Increasing the Number of Wait States

6.4 Guaranteeing RAS Low Time and RAS Precharge

Time

2.3 Refresh Signals

2.4 Port A Access Signals

7.0 RAS AND CAS CONFIGURATION MODES

7.1 Byte Writing

2.5 Port B Access Signals (DP8422A)

2.6 Common Dual Port Signals (DP8422A)

2.7 Power Signals and Capacitor Input

2.8 Clock Inputs

7.2 Memory Interleaving

7.3 Address Pipelining

7.4 Error Scrubbing

3.0 PROGRAMMING AND RESETTING

3.1 External Reset

7.5 Page/Burst Mode

8.0 TEST MODE

3.2 Programming Methods

9.0 DRAM CRITICAL TIMING PARAMETERS

3.2.1 Mode Load Only Programming

3.2.2 Chip Selected Access Programming

3.3 Internal Programming Modes

9.1 Programmable Values of t

and t

ASC

RAH

9.2 Calculation of t

and t

ASC

RAH

10.0 DUAL ACCESSING (DP8422A)

10.1 Port B Access Mode

4.0 PORT A ACCESS MODES

4.1 Access Mode 0

10.2 Port B Wait State Support

4.2 Access Mode 1

10.3 Common Port A and Port B Dual Port Functions

4.3 Extending CAS with Either Access Mode

4.4 Read-Modify-Write Cycles with Either Access Mode

4.5 Additional Access Support Features

10.3.1 GRANTB Output

10.3.2 LOCK Input

4.5.1 Address Latches and Column Increment

4.5.2 Address Pipelining

11.0 ABSOLUTE MAXIMUM RATINGS

12.0 DC ELECTRICAL CHARACTERISTICS

13.0 AC TIMING PARAMETERS

4.5.3 Delay CAS During Write Accesses

5.0 REFRESH OPTIONS

14.0 FUNCTIONAL DIFFERENCES BETWEEN THE

DP8420A/21A/22A AND THE DP8420/21/22

5.1 Refresh Control Modes

5.1.1 Automatic Internal Refresh

15.0 DP8420A/21A/22A USER HINTS

5.1.2 Externally Controlled/Burst Refresh

5.1.3 Refresh Request/Acknowledge

5.2 Refresh Cycle Types

5.2.1 Conventional Refresh

5.2.2 Staggered Refresh^TM

5.2.3 Error Scrubbing Refresh

5.3 Extending Refresh

5.4 Clearing the Refresh Address Counter

5.5 Clearing the Refresh Request Clock

2

1.0 Introduction

The DP8420A/21A/22A are CMOS Dynamic RAM control-

lers that incorporate many advanced features which include

address latches, refresh counter, refresh clock, row, column

and refresh address multiplexer, delay line, refresh/access

arbitration logic and high capacitive drivers. The program-

mable system interface allows any manufacturer’s micro-

processor or bus to directly interface via the

DP8420A/21A/22A to DRAM arrays up to 64 Mbytes in

size.

Sequential Accesses (Static Column/Page Mode):

The DP8420A/21A/22A have address latches, used to

latch the bank, row and column address inputs. Once the

address is latched, a COLumn INCrement (COLINC) feature

can be used to increment the column address. The address

latches can also be programmed to be fall through. COLINC

can be used for Sequential Accesses of Static Column

DRAMs. Also, COLINC in conjunction with ECAS inputs can

be used for Sequential Accesses to Page Mode DRAMs.

After power up, the user must first reset and program the

DP8420A/21A/22A before accessing the DRAM. The chip

is programmed through the address bus.

RAS and CAS Configuration (Byte Writing):

The RAS and CAS drivers can be configured to drive a one,

two or four bank memory array up to 32 bits in width. The

ECAS signals can then be used to select one of four CAS

drivers for Byte Writing with no extra logic.

Reset:

Due to the differences in power supplies, the internal reset

circuit may not always reset correctly; therefore, an External

(hardware) Reset must be performed before programming

the chip.

Memory Interleaving:

When configuring the DP820A/21A/22A for more than one

bank, Memory Interleaving can be used. By tying the low

order address bits to the bank select lines B0 and B1, se-

quential back to back accesses will not be delayed since

these controllers have separate precharge counters per

bank.

Programming:

After resetting the chip, the user can program the controller

by either one of two methods: Mode Load Only Program-

ming or Chip Select Access Programming.

Initialization Period:

Address Pipelining:

Once the DP8420A/21A/22A has been programmed for the

first time, a 60 ms initialization period is entered. During this

time the DRC performs refreshes to the DRAM array so

further warm up cycles are unnecessary. The initialization

period is entered only after the first programming after a

reset.

The DP8420A/21A/22A are capable of performing Address

Pipelining. In address pipelining, the DRC will guarantee the

column address hold time and switch the internal multiple-

xor to place the row address on the address bus. At this

time, another memory access to another bank can be initiat-

ed.

Accessing Modes:

Dual Accessing:

After resetting and programming the chip, the

DP8420A/21A/22A is ready to access the DRAM. There

are two modes of accessing with these controllers. Mode 0,

which indicates RAS synchronously and Mode 1, which indi-

cates RAS asynchronously.

Finally, the DP8422A has all the features previously men-

tioned and unlike the DP8420A/21A, the DP8422A has a

second port to allow a second CPU to access the same

memory array. The DP8422A has four signals to support

Dual Accessing, these signals are AREQB, ATACKB, LOCK

and GRANTB. All arbitration for the two ports and refresh is

done on chip by the controller through the insertion of wait

states. Since the DP8422A has only one input address bus,

the address lines must be multiplexed externally. The signal

GRANTB can be used for this purpose.

Refresh Modes:

The DP8420A/21A/22A have expanded refresh capabilities

compared to previous DRAM controllers. There are three

modes of refreshing available: Internal Automatic Refresh-

ing, Externally Controlled/Burst Refreshing and Refresh Re-

quest/Acknowledge Refreshing. Any of these modes can

be used together or separately to achieve the desired re-

sults.

Terminology:

The following explains the terminology used in this data

sheet. The terms negated and asserted are used. Asserted

refers to a ‘‘true’’ signal. Thus, ‘‘ECAS0 asserted’’ means

the ECAS0 input is at a logic 0. The term ‘‘COLINC assert-

ed’’ means the COLINC input is at a logic 1. The term negat-

Refresh Types:

These controllers have three types of refreshing available:

Conventional, Staggered and Error Scrubbing. Any refresh

control mode can be used with any type of refresh.

ed refers to

a ‘‘false’’ signal. Thus, ‘‘ECAS0 negated’’

means the ECAS0 input is at a logic 1. The term ‘‘COLINC

negated’’ means the input COLINC is at a logic 0. The table

shown below clarifies this terminology.

Wait Support:

The DP8420A/21A/22A have wait support available as

DTACK or WAIT. Both are programmable. DTACK, Data

Transfer ACKnowledge, is useful for processors whose wait

signal is active high. WAIT is useful for those processors

whose wait signal is active low. The user can choose either

at programming. These signals are used by the on chip arbi-

ter to insert wait states to guarantee the arbitration between

accesses, refreshes and precharge. Both signals are inde-

pendent of the access mode chosen and both signals can

be dynamically delayed further through the WAITIN signal to

the DP8420A/21A/22A.

Signal

Action

Asserted

Negated

Asserted

Negated

Logic Level

High

Active High

Active Low

Low

High

3

Connection Diagrams

TL/F/8588–4

TL/F/8588–3

Top View

FIGURE 2

Top View

FIGURE 3

Order Number DP8420AV-20 or DP8420AV-25

See NS Package Number V68A

Order Number DP8421AV-20 or DP8421AV-25

See NS Package Number V68A

TL/F/8588–2

Top View

FIGURE 4

Order Number DP8422AV-20 or DP8422AV-25

See NS Package Number V84A

4

2.0 Signal Descriptions

Device (If not

Input/

Description

Name

Applicable to All) Output

2.1 ADDRESS, R/W AND PROGRAMMING SIGNALS

R0–10

R0–9

DP8422A

I

ROW ADDRESS: These inputs are used to specify the row address during an access

to the DRAM. They are also used to program the chip when ML is asserted (except

R10).

DP8420A/21A

C0–10

C0–9

DP8422A

I

COLUMN ADDRESS: These inputs are used to specify the column address during an

access to the DRAM. They are also used to program the chip when ML is asserted

(except C10).

DP8420A/21A

B0, B1

I

BANK SELECT: Depending on programming, these inputs are used to select a group

of RAS and CAS outputs to assert during an access. They are also used to program

the chip when ML is asserted.

ECAS0–3

ENABLE CAS: These inputs are used to enable a single or group of CAS outputs

when asserted. In combination with the B0, B1 and the programming bits, these

inputs select which CAS output or CAS outputs will assert during an access. The

ECAS signals can also be used to toggle a group of CAS outputs for page/nibble

mode accesses. They also can be used for byte write operations. If ECAS0 is

negated during programming, continuing to assert the ECAS0 while negating AREQ

or AREQB during an access, will cause the CAS outputs to be extended while the

RAS outputs are negated (the ECASn inputs have no effect during scrubbing

refreshes).

WIN

I

WRITE ENABLE IN: This input is used to signify a write operation to the DRAM. If

ECAS0 is asserted during programming, the WE output will follow this input. This

input asserted will also cause CAS to delay to the next positive clock edge if address

bit C9 is asserted during programming.

COLINC

I

COLUMN INCREMENT: When the address latches are used, and RFIP is negated,

this input functions as COLINC. Asserting this signal causes the column address to

be incremented by one. When RFIP is asserted, this signal is used to extend the

refresh cycle by any number of periods of CLK until it is negated.

(EXTNDRF)

ML

I

MODE LOAD: This input signal, when low, enables the internal programming register

that stores the programming information.

2.2 DRAM CONTROL SIGNALS

Q0–10

Q0–9

Q0–8

DP8422A

DP8421A

O

DRAM ADDRESS: These outputs are the multiplexed output of the R0–9, 10 and

C0–9, 10 and form the DRAM address bus. These outputs contain the refresh

address whenever RFIP is asserted. They contain high capacitive drivers with 20X

series damping resistors.

RAS0–3

O

ROW ADDRESS STROBES: These outputs are asserted to latch the row address

contained on the outputs Q0–8, 9, 10 into the DRAM. When RFIP is asserted, the

RAS outputs are used to latch the refresh row address contained on the Q0–8, 9, 10

outputs in the DRAM. These outputs contain high capacitive drivers with 20X series

damping resistors.

CAS0–3

O

COLUMN ADDRESS STROBES: These outputs are asserted to latch the column

address contained on the outputs Q0–8, 9, 10 into the DRAM. These outputs have

high capacitive drivers with 20X series damping resistors.

WE

O

WRITE ENABLE or REFRESH REQUEST: This output asserted specifies a write

operation to the DRAM. When negated, this output specifies a read operation to the

DRAM. When the DP8420A/21A/22A is programmed in address pipelining mode or

when ECAS0 is negated during programming, this output will function as RFRQ.

When asserted, this pin specifies that 13 ms or 15 ms have passed. If DISRFSH is

negated, the DP8420A/21A/22A will perform an internal refresh as soon as possible.

If DISRFRSH is asserted, RFRQ can be used to externally request a refresh through

the input RFSH. This output has a high capacitive driver and a 20X series damping

resistor.

(RFRQ)

5

2.0 Signal Descriptions (Continued)

Device (If not

Input/

Description

Name

Applicable to All) Output

2.3 REFRESH SIGNALS

RFIP

O

I

REFRESH IN PROGRESS: This output is asserted prior to a refresh cycle and is

negated when all the RAS outputs are negated for that refresh.

RFSH

REFRESH: This input asserted with DISRFRSH already asserted will request a

refresh. If this input is continually asserted, the DP8420A/21A/22A will perform

refresh cycles in a burst refresh fashion until the input is negated. If RFSH is asserted

with DISRFSH negated, the internal refresh address counter is cleared (useful for

burst refreshes).

DISRFSH

I

DISABLE REFRESH: This input is used to disable internal refreshes and must be

asserted when using RFSH for externally requested refreshes.

2.4 PORT A ACCESS SIGNALS

ADS

I

ADDRESS STROBE or ADDRESS LATCH ENABLE: Depending on programming,

this input can function as ADS or ALE. In mode 0, the input functions as ALE and

when asserted along with CS causes an internal latch to be set. Once this latch is set

an access will start from the positive clock edge of CLK as soon as possible. In Mode

1, the input functions as ADS and when asserted along with CS, causes the access

RAS to assert if no other event is taking place. If an event is taking place, RAS will be

asserted from the positive edge of CLK as soon as possible. In both cases, the low

going edge of this signal latches the bank, row and column address if programmed to

do so.

(ALE)

CS

I

CHIP SELECT: This input signal must be asserted to enable a Port A access.

AREQ

ACCESS REQUEST: This input signal in Mode 0 must be asserted some time after

the first positive clock edge after ALE has been asserted. When this signal is

negated, RAS is negated for the access. In Mode 1, this signal must be asserted

before ADS can be negated. When this signal is negated, RAS is negated for the

access.

WAIT

O

WAIT or DTACK: This output can be programmed to insert wait states into a CPU

access cycle. With R7 negated during programming, the output will function as a

WAIT type output. In this case, the output will be active low to signal a wait condition.

With R7 asserted during programming, the output will function as DTACK. In this

case, the output will be negated to signify a wait condition and will be asserted to

signify the access has taken place. Each of these signals can be delayed by a

number of positive clock edges or negative clock levels of CLK to increase the

microprocessor’s access cycle through the insertion of wait states.

(DTACK)

WAITIN

I

WAIT INCREASE: This input can be used to dynamically increase the number of

positive clock edges of CLK until DTACK will be asserted or WAIT will be negated

during a DRAM access.

6

2.0 Signal Descriptions (Continued)

Device (If not

Input/

Description

Name

Applicable to All)

Output

2.5 PORT B ACCESS SIGNALS

AREQB

DP8422A

only

I

PORT B ACCESS REQUEST: This input asserted will latch the row, column and bank

address if programmed, and requests an access to take place for Port B. If the

access can take place, RAS will assert immediately. If the access has to be delayed,

RAS will assert as soon as possible from a positive edge of CLK.

ATACKB

DP8422A

only

O

ADVANCED TRANSFER ACKNOWLEDGE PORT B: This output is asserted when

the access RAS is asserted for a Port B access. This signal can be used to generate

the appropriate DTACK or WAIT type signal for Port B’s CPU or bus.

2.6 COMMON DUAL PORT SIGNALS

GRANTB

LOCK

DP8422A

only

O

GRANT B: This output indicates which port is currently granted access to the DRAM

array. When GRANTB is asserted, Port B has access to the array. When GRANTB is

negated, Port A has access to the DRAM array. This signal is used to multiplex the

signals R0–8, 9, 10; C0–8, 9, 10; B0–1; WIN; LOCK and ECAS0–3 to the DP8422A

when using dual accessing.

DP8422A

only

I

LOCK: This input can be used by the currently granted port to ‘‘lock out’’ the other

port from the DRAM array by inserting wait states into the locked out port’s access

cycle until LOCK is negated.

2.7 POWER SIGNALS AND CAPACITOR INPUT

V

I

POWER: Supply Voltage.

CC

GND

CAP

GROUND: Supply Voltage Reference.

CAPACITOR: This input is used by the internal PLL for stabilization. The value of the

ceramic capacitor should be 0.1 mF and should be connected between this input and

ground.

2.8 CLOCK INPUTS

There are two clock inputs to the DP8420A/21A/22A, CLK and DELCLK. These two clocks may both be tied to the same clock

input, or they may be two separate clocks, running at different frequencies, asynchronous to each other.

CLK

I

SYSTEM CLOCK: This input may be in the range of 0 Hz up to 25 MHz. This input is

generally a constant frequency but it may be controlled externally to change

frequencies or perhaps be stopped for some arbitrary period of time.

This input provides the clock to the internal state machine that arbitrates between

accesses and refreshes. This clock’s positive edges and negative levels are used to

extend the WAIT (DTACK) signals. Ths clock is also used as the reference for the

RAS precharge time and RAS low time during refresh.

All Port A and Port B accesses are assumed to be synchronous to the system clock

CLK.

DELCLK

I

DELAY LINE CLOCK: The clock input DELCLK, may be in the range of 6 MHz to

20 MHz and should be a multiple of 2 (i.e., 6, 8, 10, 12, 14, 16, 18, 20 MHz) to have

the DP8420A/21A/22A switching characteristics hold. If DELCLK is not one of the

above frequencies the accuracy of the internal delay line will suffer. This is because

the phase locked loop that generates the delay line assumes an input clock

frequency of a multiple of 2 MHz.

For example, if the DELCLK input is at 7 MHz and we choose a divide by 3 (program

bits C0–2) this will produce 2.333 MHz which is 16.667% off of 2 MHz. Therefore, the

DP8420A/21A/22A delay line would produce delays that are shorter (faster delays)

than what is intended. If divide by 4 was chosen the delay line would be longer

(slower delays) than intended (1.75 MHz instead of 2 MHz). (See Section 10 for more

information.)

This clock is also divided to create the internal refresh clock.

7

3.0 Programming and Resetting

Due to the variety in power supplies power-up times, the

internal power up reset circuit may not work in every design;

therefore, an EXTERNAL RESET must be performed before

the DRAM controller can be programmed and used.

3.1 EXTERNAL RESET

At power up, if the internal power up reset worked, all inter-

nal latches and flip-flops are cleared and the part is ready to

be programmed. The power up state can also be achieved

by performing an External Reset, which is required to insure

proper operation. External Reset is achieved by asserting

ML and DISRFSH for at least 16 positive clock edges. In

order to perform simply a Reset, the ML signal must be

negated before DISRFSH is negated as shown in Figure 5a.

This procedure will only reset the controller which now is

ready for programming.

After going through the reset procedure, the

DP8420A/21A/22A can be programmed by either of two

methods; Mode Load Only Programming or Chip Select Ac-

cess Programming. After programming the DRC for the first

time after reset, the chip enters a 60 ms initialization period,

during this period the controller performs refreshes every

13 ms or 15 ms, this makes further DRAM warm up cycles

unnecessary. After this stage the chip can be repro-

grammed as many times as the user wishes and the 60 ms

period will not be entered into unless the chip is reset and

programmed again.

While performing an External Reset, if the user negates

DISRFSH at least one clock period before negating ML, as

shown in Figure 5b, ML negated will program the

DP8420A/21A/22A with the values in R0–9, C0–9, B0–1

and ECAS0. The 60 ms initialization period will be entered

since it is the first programming after reset. This is a good

way of resetting and programming the part at the same time.

Make sure the right programming bits are on the address

lines before ML is negated.

During the 60 ms initialization period, RFIP is asserted low

and RAS toggles every 13 ms or 15 ms depending on the

programming bit for refresh (C3). CAS will be inactive (logic

1) and the ‘‘Q’’ outputs will count from 0 to 2047 refreshing

the entire DRAM array. The actual initialization time period

e

is given by the following formula. T

4096* (Clock Divisor

The DRC may be Reset and programmed any time on the

fly, but the user must make sure that No Access or Refresh

is in progress.

Select)* (Refresh Clock Fine Tune)/(DELCLK Frq.)

TL/F/8588–E1

FIGURE 5a. Chip Reset but Not Programmed

TL/F/8588–E2

FIGURE 5b. Chip Reset and Programmed

8

3.0 Programming and Resetting (Continued)

3.2 PROGRAMMING METHODS

3.2.1 Mode Load Only Programming

3.2.2 Chip Selected Access Programming

To use this method the user asserts ML enabling the inter-

nal programming register. After ML is asserted, a valid pro-

gramming selection is placed on the address bus, B0, B1

and ECAS0 inputs, then ML is negated. When ML is negat-

ed the programming bits are latched into the internal pro-

gramming register and the DP8420A/21A/22A is pro-

grammed, see Figure 6. When programming the chip, the

controller must not be refreshing, RFIP must be high (1) to

have a successful programming.

The chip can also be programmed by performing a chip

selected access. To program the chip using this method,

ML is asserted, then CS is asserted and a valid program-

ming selection is placed on the address bus. When AREQ is

asserted, the programming bits affecting the wait logic be-

come effective immediately, then DTACK is asserted allow-

ing the access to terminate. After the access, ML is negated

and the rest of the programming bits take effect.

TL/F/8588–G3

FIGURE 6. ML Only Programming

TL/F/8588–G4

FIGURE 7. CS Access Programming

9

3.0 Programming and Resetting (Continued)

3.3 PROGRAMMING BIT DEFINITIONS

Symbol

Description

ECAS0

Extend CAS/Refresh Request Select

0

The CASn outputs will be negated with the RASn outputs when AREQ (or AREQB, DP8422A only) is negated.

The WE output pin will function as write enable.

1

The CASn outputs will be negated, during an acccess (Port A (or Port B, DP8422A only)) when their

corresponding ECASn inputs are negated. This feature allows the CAS outputs to be extended beyond the RAS

outputs negating. Scrubbing refreshes are NOT affected. During scrubbing refreshes the CAS outputs will negate

along with the RAS outputs regardless of the state of the ECAS inputs.

The WE output will function as ReFresh ReQuest (RFRQ) when this mode is programmed.

B1

Access Mode Select

0

ACCESS MODE 0: ALE pulsing high sets an internal latch. On the next positive edge of CLK, the access (RAS)

will start. AREQ will terminate the access.

1

ACCESS MODE 1: ADS asserted starts the access (RAS) immediately. AREQ will terminate the access.

B0

0

Address Latch Mode

ADS or ALE asserted for Port A or AREQB asserted for Port B with the appropriate GRANT latch the input row,

column and bank address.

1

The row, column and bank latches are fall through.

Delay CAS during WRITE Accesses

C9

0

1

CAS is treated the same for both READ and WRITE accesses.

During WRITE accesses, CAS will be asserted by the event that occurs last: CAS asserted by the internal delay

line or CAS asserted on the positive edge of CLK after RAS is asserted.

C8

Row Address Hold Time

e

0

1

Row Address Hold Time

25 ns minimum

15 ns minimum

C7

Column Address Setup Time

e

0

1

Column Address Setup Time

10 ns miniumum

0 ns minimum

e

C6, C5, C4

RAS and CAS Configuration Modes/Error Scrubbing during Refresh

0, 0, 0

RAS0–3 and CAS0–3 are all selected during an access. ECASn must be asserted for CASn to be asserted.

B0 and B1 are not used during an access. Error scrubbing during refresh.

0, 0, 1

RAS and CAS pairs are selected during an access by B1. ECASn must be asserted for CASn to be asserted.

e

B1

0 during an access selects RAS0–1 and CAS0–1.

1 during an access selects RAS2–3 and CAS2–3.

B0 is not used during an Access.

Error scrubbing during refresh.

0, 1, 0

RAS and CAS singles are selected during an access by B0–1. ECASn must be asserted for CASn to be asserted.

e

B1

0, B0

1, B0

0 during an access selects RAS0 and CAS0.

1 during an access selects RAS1 and CAS1.

0 during an access selects RAS2 and CAS2.

1 during an access selects RAS3 and CAS3.

Error scrubbing during refresh.

0, 1, 1

1, 0, 0

RAS0–3 and CAS0–3 are all selected during an access. ECASn must be asserted for CASn to be asserted.

B1, B0 are not used during an access.

No error scrubbing. (RAS only refreshing)

RAS pairs are selected by B1. CAS0–3 are all selected. ECASn must be asserted for CASn to be asserted.

e

B1

0 during an access selects RAS0–1 and CAS0–3.

1 during an access selects RAS2–3 and CAS0–3.

B0 is not used during an access.

No error scrubbing.

10

3.0 Programming and Resetting (Continued)

3.3 PROGRAMMING BIT DEFINITIONS (Continued)

Symbol

Description

C6, C5, C4

RAS and CAS Configuration Modes (Continued)

1, 0, 1

RAS and CAS pairs are selected by B1. ECASn must be asserted for CASn to be asserted.

e

B1

0 during an access selects RAS0–1 and CAS0–1.

1 during an access selects RAS2–3 and CAS2–3.

B0 is not used during an access.

No error scrubbing.

1, 1, 0

RAS singles are selected by B0–1. CAS0–3 are all selected. ECASn must be asserted for CASn to be

asserted.

e

B1

0, B0

1, B0

0 during an access selects RAS0 and CAS0–3.

1 during an access selects RAS1 and CAS0–3.

0 during an access selects RAS2 and CAS0–3.

1 during an access selects RAS3 and CAS0–3.

No error scrubbing.

1, 1, 1

RAS and CAS singles are selected by B0, 1. ECASn must be asserted for CASn to be asserted.

e

B1

0, B0

1, B0

0 during an access selects RAS0 and CAS0.

1 during an access selects RAS1 and CAS1.

0 during an access selects RAS2 and CAS2.

1 during an access selects RAS3 and CAS3.

No error scrubbing.

C3

Refresh Clock Fine Tune Divisor

e

0

Divide delay line/refresh clock further by 30 (If DELCLK/Refresh Clock Clock Divisor

refresh period).

2 MHz

15 ms

13 ms

1

Divide delay line/refresh clock further by 26 (If DELCLK/Refresh Clock Clock Divisor

refresh period).

C2, C1, C0

Delay Line/Refresh Clock Divisor Select

0, 0, 0

0, 0, 1

0, 1, 0

0, 1, 1

1, 0, 0

1, 0, 1

1, 1, 0

1, 1, 1

Divide DELCLK by 10 to get as close to 2 MHz as possible.

Divide DELCLK by 9 to get as close to 2 MHz as possible.

Divide DELCLK by 8 to get as close to 2 MHz as possible.

Divide DELCLK by 7 to get as close to 2 MHz as possible.

Divide DELCLK by 6 to get as close to 2 MHz as possible.

Divide DELCLK by 5 to get as close to 2 MHz as possible.

Divide DELCLK by 4 to get as close to 2 MHz as possible.

Divide DELCLK by 3 to get as close to 2 MHz as possible.

R9

Refresh Mode Select

0

1

RAS0–3 will all assert and negate at the same time during a refresh.

Staggered Refresh. RAS outputs during refresh are separated by one positive clock edge. Depending on the

configuration mode chosen, either one or two RASs will be asserted.

R8

Address Pipelining Select

0

Address pipelining is selected. The DRAM controller will switch the DRAM column address back to the row

address after guaranteeing the column address hold time.

1

Non-address pipelining is selected. The DRAM controller will hold the column address on the DRAM address

bus until the access RASs are negated.

R7

WAIT or DTACK Select

0

1

WAIT type output is selected.

DTACK (Data Transfer ACKnowledge) type output is selected.

R6

Add Wait States to the Current Access if WAITIN is Low

0

1

WAIT or DTACK will be delayed by one additional positive edge of CLK.

WAIT or DTACK will be delayed by two additional positive edges of CLK.

11

3.0 Programming and Resetting (Continued)

3.3 PROGRAMMING BIT DEFINITIONS (Continued)

Symbol

R5, R4

0, 0

Description

WAIT/DTACK during Burst (See Section 5.1.2 or 5.2.2)

e

NO WAIT STATES; If R7

0 during programming, WAIT will remain negated during burst portion of access.

e

If R7

1T; If R7

WAIT will negate from the positive edge of CLK after the ECASs have been asserted.

1 programming, DTACK will remain asserted during burst portion of access.

e

0, 1

1, 0

1, 1

0 during programming, WAIT will assert when the ECAS inputs are negated with AREQ asserted.

e

DTACK will assert from the positive edge of CLK after the ECASs have been asserted.

If R7

1 during programming, DTACK will negate when the ECAS inputs are negated with AREQ asserted.

e

WAIT will negate on the negative level of CLK after the ECASs have been asserted.

(/2T; If R7

0 during programming, WAIT will assert when the ECAS inputs are negated with AREQ asserted.

e

DTACK will assert from the negative level of CLK after the ECASs have been asserted.

If R7

1 during programming, DTACK will negate when the ECAS inputs are negated with AREQ asserted.

e

the ECAS inputs are asserted.

0T; If R7

0 during programming, WAIT will assert when the ECAS inputs are negated. WAIT will negate when

e

the ECAS inputs are asserted.

If R7

1 during programming, DTACK will negate when the ECAS inputs are negated. DTACK will assert when

R3, R2

WAIT/DTACK Delay Times (See Section 5.1.1 or 5.2.1)

e

NO WAIT STATES; If R7 0 during programming, WAIT will remain high during non-delayed accesses. WAIT

will negate when RAS is negated during delayed accesses.

0, 0

e

NO WAIT STATES; If R7

1 during programming, DTACK will be asserted when RAS is asserted.

e

(/2T; If R7

0, 1

1, 0

0 during programming, WAIT will negate on the negative level of CLK, after the access RAS.

e

1T; If R7

1 during programming, DTACK will be asserted on the positive edge of CLK after the access RAS.

e

NO WAIT STATES, (/2T; If R7

WAIT will negate on the negative level of CLK, after the access RAS, during delayed accesses.

0 during programming, WAIT will remain high during non-delayed accesses.

e

(/2T; If R7

1 during programming, DTACK will be asserted on the negative level of CLK after the access RAS.

e

0 during programming, WAIT will negate on the positive edge of CLK after the access RAS.

1, 1

1T; If R7

e

of CLK after the access RAS.

1(/2T; If R7

1 during programming, DTACK will be asserted on the negative level of CLK after the positive edge

R1, R0

RAS Low and RAS Precharge Time

e

0, 0

RAS asserted during refresh

2 positive edges of CLK.

1 positive edge of CLK.

RAS will start from the first positive edge of CLK after GRANTB transitions (DP8422A).

e

RAS precharge time

e

0, 1

1, 0

1, 1

RAS asserted during refresh

3 positive edges of CLK.

2 positive edges of CLK.

RAS will start from the second positive edge of CLK after GRANTB transitions (DP8422A).

e

RAS precharge time

e

RAS asserted during refresh

2 positive edges of CLK.

RAS will start from the first positive edge of CLK after GRANTB transitions (DP8422A).

e

RAS precharge time

e

RAS asserted during refresh

4 positive edges of CLK.

3 positive edges of CLK.

RAS will start from the second positive edge of CLK after GRANTB transitions (DP8422A).

e

RAS precharge time

12

4.0 Port A Access Modes

The DP8420A/21A/22A have two general purpose access

modes. Mode 0 RAS synchronous and Mode 1 RAS asyn-

chronous. One of these modes is selected at programming

through the B1 input. A Port A access to DRAM is initiated

by two input signals: ADS (ALE) and CS. The access is al-

ways terminated by one signal: AREQ. These input signals

should be synchronous to the input clock.

first rising edge of clock. If a refresh or a Port B access is in

progress or precharge time is required, the controller will

wait until these events have taken place and assert RAS

(RASs) on the next positive edge of clock.

Sometime after the first positive edge of clock after ALE and

CS have been asserted, the input AREQ must be asserted.

In single port applications, once AREQ is asserted, CS can

be negated. On the other hand, ALE can stay asserted sev-

eral periods of clock; however, ALE must be negated before

or during the period of CLK in which AREQ is negated.

4.1 ACCESS MODE 0

Mode 0, synchronous access, is selected by negating the

e

input B1 during programming (B1 0). To initiate a Mode 0

The controller samples AREQ on the every rising edge of

clock after DTACK is asserted. The access will end when

AREQ is sampled negated.

access, ALE is pulse high and CS is asserted. If precharge

time was met, a refresh of DRAM or a Port B access was

not in progress, the RAS (RASs) would be asserted on the

TL/F/8588–60

FIGURE 8a. Access Mode 0

13

4.0 Port A Access Modes (Continued)

en place and assert RAS (RASs) from the next rising edge

of clock.

4.2 ACCESS MODE 1

Mode 1, asynchronous access, is selected by asserting the

e

When ADS is asserted or sometime after, AREQ must be

asserted. At this time, ADS can be negated and AREQ will

continue the access. Also, ADS can continue to be asserted

after AREQ has been asserted and negated; however, a

new access will not start until ADS is negated and asserted

again. When address pipelining is not implemented, ADS

and AREQ can be tied together.

input B1 during programming (B1 1). This mode allows ac-

cesses to start immediately from the access request input,

ADS. To initiate a Mode 1 access, CS is asserted followed

by ADS asserted. If precharge time was met, a refresh of

the DRAM or a Port B access was not in progress, the RAS

(RASs) would be asserted from ADS being asserted. If a

refresh or Port B access is in progress or precharge time is

required, the controller will wait until these events have tak-

The access will end when AREQ is negated.

TL/F/8588–62

FIGURE 8b. Access Mode 1

14

4.0 Port A Access Modes (Continued)

with AREQ. If ECAS0 was negated (1) during programming,

CAS (CASs) will continue to be asserted after RAS has

been negated, given that the appropriate ECAS inputs are

asserted. This allows a DRAM to have data present on the

data out bus while gaining RAS precharge time.

4.3 EXTENDING CAS WITH EITHER ACCESS MODE

In both access modes, once AREQ is negated, RAS and

DTACK if programmed will be negated. If ECAS0 was as-

serted (0) during programming, CAS (CASs) will be negated

TL/F/8588–61

FIGURE 9a. Access Mode 0 Extending CAS

TL/F/8588–63

FIGURE 9b. Access Mode 1 Extending CAS

15

4.0 Port A Access Modes (Continued)

4.4 READ-MODIFY-WRITE CYCLES WITH EITHER ACCESS MODE

There are 2 methods by which this chip can be used to do

read-modify-write access cycles. The first method involves

doing a late write access where the WIN input is asserted

some delay after CAS is asserted. The second method in-

volves doing a page mode read access followed by a page

mode write access with RAS held low (see Figure 9c ).

WIN from negated to asserted in a late write access be-

cause here a problem may arise with DATA IN and DATA

OUT being valid at the same time. This may result in a data

line trying to drive two different levels simultaneously. The

page mode method of a read-modify-write access allows

the user to have transceivers in the system because the

data in (read data) is guaranteed to be high impedance dur-

ing the time the data out (write data) is valid.

CASn must be toggled using the ECASn inputs and WIN has

to be changed from negated to asserted (read to write)

while CAS is negated. This method is better than changing

TL/F/8588–G2

*There may be idle states inserted here by the CPU.

FIGURE 9c. Read-Modify-Write Access Cycle

16

4.0 Port A Access Modes (Continued)

In Mode 1, the address latches are in fall through mode until

ADS is asserted. ADS asserted latches the address.

4.5 ADDITIONAL ACCESS SUPPORT FEATURES

To support the different modes of accessing, the

DP8420A/21A/22A offer other access features. These ad-

ditional features include: Address Latches and Column In-

crement (for page/burst mode support), Address Pipelining,

and Delay CAS (to allow the user with a multiplexed bus to

ensure valid data is present before CAS is asserted).

Once the address is latched, the column address can be

incremented with the input COLINC. COLINC can be used

for sequential accesses of static column DRAMs. COLINC

can also be used with the ECAS inputs to support sequen-

tial accesses to page mode DRAMs as shown in Figure 10.

COLINC should only be asserted when the signal RFIP is

negated during an access since this input functions as ex-

tended refresh when RFIP is asserted. COLINC must be

negated (0) when the address is being latched (ADS falling

edge in Mode 1). If COLINC is asserted with all of the bits of

the column address asserted (ones), the column address

will return to zero.

4.5.1 Address Latches and Column Increment

The Address Latches can be programmed, through pro-

gramming bit B0. They can be programmed to either latch

the address or remain in a fall-through mode. If the address

latches are used to latch the address, the controller will

function as follows:

In Mode 0, the rising edge of ALE places the latches in fall-

through, once ALE is negated, the address present in the

row, column and bank input is latched.

TL/F/8588–C4

FIGURE 10. Column Increment

The address latches function differently with the DP8422A.

The DP8422A will latch the address of the currently granted

port. If Port A is currently granted, the address will be

latched as described in Section 4.5.1. If Port A is not grant-

ed, and requests an access, the address will be latched on

the first or second positive edge of CLK after GRANTB has

been negated depending on the programming bits R0, R1.

For Port B, if GRANTB is asserted, the address will be

latched with AREQB asserted. If GRANTB is negated, the

address will latch on the first or second positive edge of

CLK after GRANTB is asserted depending on the program-

ming bits R0, R1.

17

4.0 Port A Access Modes (Continued)

During address pipelining in Mode 0, shown in Figure 11c,

ALE cannot be pulsed high to start another access until

AREQ has been asserted for the previous access for at

least one period of CLK. DTACK, if programmed, will be

negated once AREQ is negated. WAIT, if programmed to

insert wait states, will be asserted once ALE and CS are

asserted.

4.5.2 Address Pipelining

Address pipelining is the overlapping of accesses to differ-

ent banks of DRAM. If the majority of successive accesses

are to a different bank, the accesses can be overlapped.

Because of this overlapping, the cycle time of the DRAM

accesses are greatly reduced. The DP8420A/21A/22A can

be programmed to allow a new row address to be placed on

the DRAM address bus after the column address hold time

has been met. At this time, a new access can be initiated

with ADS or ALE, depending on the access mode, while

AREQ is used to sustain the current access. The DP8422A

supports address pipelining for Port A only. This mode can-

not be used with page, static column or nibble modes of

operations because the DRAM column address is switched

back to the row address after CAS is asserted. This mode is

programmed through address bit R8 (see Figures 11a and

11b). In this mode, the output WE always functions as

RFRQ.

In Mode 1, shown in Figure 11d, ADS can be negated once

AREQ is asserted. After meeting the minimum negated

pulse width for ADS, ADS can again be asserted to start a

new access. DTACK, if programmed, will be negated once

AREQ is negated. WAIT, if programmed, will be asserted

once ADS is asserted.

In either mode with either type of wait programmed, the

DP8420A/21A/22A will still delay the access for precharge

if sequential accesses are to the same bank or if a refresh

takes place.

TL/F/8588–G0

FIGURE 11a. Non-Address Pipelined Mode

TL/F/8588–G1

FIGURE 11b. Address Pipelined Mode

18

4.0 Port A Access Modes (Continued)

19

4.0 Port A Access Modes (Continued)

4.5.3 Delay CAS during Write Accesses

Address bit C9 asserted during programming will cause CAS

to be delayed until the first positive edge of CLK after RAS

is asserted when the input WIN is asserted. Delaying CAS

during write accesses ensures that the data to be written to

DRAM will be setup to CAS asserting as shown in Figures

12a and 12b. If the possibility exists that data still may not

be present after the first positive edge of CLK, CAS can be

delayed further with the ECAS inputs. If address bit C9 is

negated during programming, read and write accesses will

be treated the same (with regard to CAS).

TL/F/8588–C7

FIGURE 12a. Mode 0 Delay CAS

TL/F/8588–C8

FIGURE 12b. Mode 1 Delay CAS

20

5.0 Refresh Options

The DP8420A/21A/22A support three refresh control mode

options:

In every combination of refresh control mode and refresh

type, the DP8420A/21A/22A is programmed to keep RAS

asserted a number of CLK periods. The time values of RAS

low during refresh are programmed through programming

bits R0 and R1.

1. Automatic Internally Controlled Refresh.

2. Externally Controlled/Burst Refresh.

3. Refresh Request/Acknowledge.

5.1 REFRESH CONTROL MODES

5.1.1. Automatic Internal Refresh

With each of the control modes above, three types of re-

fresh can be performed.

1. All RAS Refresh.

The DP8420A/21A/22A have an internal refresh clock. The

period of the refresh clock is generated from the program-

ming bits C0–3. Every period of the refresh clock, an inter-

nal refresh request is generated. As long as a DRAM ac-

cess is not currently in progress and precharge time has

been met, the internal refresh request will generate an auto-

matic internal refresh. If a DRAM access is in progress, the

DP8420A/21A/22A on-chip arbitration logic will wait until

the access is finished before performing the refresh. The

refresh/access arbitration logic can insert a refresh cycle

between two address pipelined accesses. However, the re-

fresh arbitration logic can not interrupt an access cycle to

perform a refresh. To enable automatic internally controlled

refreshes, the input DISRFSH must be negated.

2. Staggered Refresh.

3. Error Scrubbing During All RAS Refresh.

There are three inputs, EXTNDRF, RFSH and DISRFSH,

and two outputs, RFIP and RFRQ, associated with refresh.

There are also ten programming bits: R0–1, R9, C0–6 and

ECAS0 used to program the various types of refreshing.

Asserting the input EXTNDRF, extends the refresh cycle for

a single or multiple integral periods of CLK.

The output RFIP is asserted one period of CLK before the

first refresh RAS is asserted. If an access is currently in

progress, RFIP will be asserted up to one period of CLK

before the first refresh RAS, after AREQ or AREQB is nega-

ted for the access (see Figure 13 ).

The DP8420A/21A/22A will increment the refresh address

counter automatically, independent of the refresh mode

used. The refresh address counter will be incremented once

all the refresh RASs have been negated.

TL/F/8588–F8

Explanation of Terms

e

RFRQ

RFSH

ReFresh ReQuest internal to the DP8420A/21A/22A. RFRQ has the ability to hold off a pending access.

Externally requested ReFreSH

ReFresh in Progress

e

RFIP

ACIP

e

Port A or Port B (DP8422A only) ACcess in Progress. This means that either RAS is low for an access or is in the process of

transitioning low for an access.

FIGURE 13. DP8420A/21A/22A Access/Refresh Arbitration State Program

21

5.0 Refresh Options (Continued)

5.1.2 Externally Controlled/Burst Refresh

take place on the next positive edge of CLK as shown in

Figure 14a. If an access to DRAM is in progress or pre-

charge time for the last access has not been met, the re-

fresh will be delayed. Since pulsing RFSH low sets a latch,

the user does not have to keep RFSH low until the refresh

starts. When the last refresh RAS negates, the internal re-

fresh request latch is cleared.

To use externally controlled/burst refresh, the user must

disable the automatic internally controlled refreshes by as-

serting the input DISRFSH. The user is responsible for gen-

erating the refresh request by asserting the input RFSH.

Pulsing RFSH low, sets an internal latch, that is used to

produce the internal refresh request. The refresh cycle will

TL/F/8588–64

FIGURE 14a. Single External Refreshes (2 Periods of RAS Low during Refresh Programmed)

By keeping RFSH asserted past the positive edge of CLK

which ends the refresh cycle as shown in Figure 14b, the

user will perform another refresh cycle. Using this tech-

nique, the user can perform a burst refresh consisting of any

number of refresh cycles. Each refresh cycle during a burst

refresh will meet the refresh RAS low time and the RAS

precharge time (programming bits R0–1).

If the user desires to burst refresh the entire DRAM (all row

addresses) he could generate an end of count signal (burst

refresh

finished)

by

looking

at

one

of

the

DP8420A/21A/22A high address outputs (Q7, Q8, Q9 or

Q10) and the RFIP output. The Qn outputs function as a

decode of how many row addresses have been refreshed

e

freshes, Q10

e

1024 refreshes).

e

512 re-

(Q7

128 refreshes, Q8

e

256 refreshes, Q9

TL/F/8588–65

FIGURE 14b. External Burst Refresh (2 Periods of RAS Precharge,

2 Periods of Refresh RAS Low during Refresh Programmed)

22

5.0 Refresh Options (Continued)

5.1.3 Refresh Request/Acknowledge

The DP8420A/21A/22A can be programmed to output in-

ternal refresh requests. When the user programs ECAS0

negated (1) and/or address pipelining mode is selected, the

WE output functions as RFRQ. RFRQ (WE) will be asserted

by one of two events:

First, if DISRFSH is negated, an automatic internal refresh

will take place. See Figure 15b.

Second, with DISRFSH asserted, RFRQ will stay asserted

until RFSH is pulsed low . This option will cause an external-

ly requested/burst refresh to take place. See Figure 15c.

First, when the external circuitry pulses low the input RFSH

which will request an external refresh.

RFRQ will go high and then assert (toggle) if additional peri-

ods of the internal refresh clock have expired and neither an

externally controlled refresh nor an automatically controlled

internal refresh have taken place, see Figure 15d. If a time

critical event, or long accesses like page/static column

mode can not be interrupted, RFRQ pulsing high can be

used to increment a counter. This counter can be used to

perform a burst refresh of the number of refreshes missed

(through the RFSH input).

Second, when the internal refresh clock has expired, which

signals that another refresh is needed.

An example of the first case, where an external refresh is

requested while RFRQ is negated (1), is shown in Figure

15a. Notice that RFRQ will be asserted from a positive edge

of clock.

On the second case, when the RFRQ is asserted from the

expiration of the internal refresh clock, the user has two

options:

TL/F/8588–66

FIGURE 15a. Externally Controlled Single and Burst Refresh with Refresh Request

(RFRQ) Output (2 Periods of RAS Low during Refresh Programmed)

TL/F/8588–67

FIGURE 15b. Automatic Internal Refresh with Refresh Request (3T of RAS Low during Refresh Programmed)

23

5.0 Refresh Options (Continued)

24

5.0 Refresh Options (Continued)

5.2 REFRESH CYCLE TYPES

Three different types of refresh cycles are available for use.

The three different types are mutually exclusive and can be

used with any of the three modes of refresh control. The

three different refresh cycle types are: all RAS refresh, stag-

gered RAS refresh and error scrubbing during all RAS re-

fresh. In all refresh cycle types, the RAS precharge time is

guaranteed: between the previous access RAS ending and

the refresh RAS0 starting; between refresh RAS3 ending

and access RAS beginning; between burst refresh RASs.

5.2.1 Conventional RAS Refresh

A conventional refresh cycle causes RAS0–3 to all assert

from the first positive edge of CLK after RFIP is asserted as

shown in Figure 16. RAS0–3 will stay asserted until the

number of positive edges of CLK programmed have passed.

On the last positive edge, RAS0–3, and RFIP will be negat-

ed. This type of refresh cycle is programmed by negating

address bit R9 during programming.

TL/F/8588–69

FIGURE 16. Conventional RAS Refresh

5.2.2 Staggered RAS Refresh

A staggered refresh staggers each RAS or group of RASs

by a positive edge of CLK as shown in Figure 17. The num-

ber of RASs, which will be asserted on each positive edge

of CLK, is determined by the RAS, CAS configuration mode

programming bits C4–C6. If single RAS outputs are select-

ed during programming, then each RAS will assert on suc-

cessive positive edges of CLK. If two RAS outputs are se-

lected during programming then RAS0 and RAS1 will assert

on the first positive edge of CLK after RFIP is asserted.

RAS2 and RAS3 will assert on the second positive edge of

CLK after RFIP is asserted. If all RAS outputs were selected

during programming, all RAS outputs would assert on the

first positive edge of CLK after RFIP is asserted. Each RAS

or group of RASs will meet the programmed RAS low time

and then negate.

TL/F/8588–70

FIGURE 17. Staggered RAS Refresh

25

5.0 Refresh Options (Continued)

5.2.3 Error Scrubbing during Refresh

tend refresh, EXTNDRF, and a read-modify-write operation

can be performed by asserting WE. It is the responsibility of

the designer to ensure that WE is negated. The DP8422A

has a 24-bit internal refresh address counter that contains

The DP8420A/21A/22A support error scrubbing during all

RAS DRAM refreshes. Error scrubbing during refresh is se-

lected through bits C4–C6 with bit R9 negated during pro-

gramming. Error scrubbing can not be used with staggered

refresh (see Section 8.0). Error scrubbing during refresh al-

lows a CAS or group of CASs to assert during the all RAS

refresh as shown in Figure 18. This allows data to be read

from the DRAM array and passed through an Error Detec-

tion And Correction Chip, EDAC. If the EDAC determines

that the data contains a single bit error and corrects that

error, the refresh cycle can be extended with the input ex-

the 11 row, 11 column and

2 bank addresses. The

DP8420A/21A have a 22-bit internal refresh address coun-

ter that contains the 10 row, 10 column and 2 bank address-

es. These counters are configured as bank, column, row

with the row address as the least significant bits. The bank

counter bits are then used with the programming selection

to determine which CAS or group of CASs will assert during

a refresh.

TL/F/8588–46

FIGURE 18. Error Scrubbing during Refresh

26

5.0 Refresh Options (Continued)

5.3 EXTENDING REFRESH

5.4 CLEARING THE REFRESH ADDRESS COUNTER

The programmed number of periods of CLK that refresh

RASs are asserted can be extended by one or multiple peri-

ods of CLK. Only the all RAS (with or without error scrub-

bing) type of refresh can be extended. To extend a refresh

cycle, the input extend refresh, EXTNDRF, must be assert-

ed before the positive edge of CLK that would have negated

all the RAS outputs during the refresh cycle and after the

positive edge of CLK which starts all RAS outputs during the

refresh as shown inFigure 19. This will extend the refresh to

the next positive edge of CLK and EXTNDRF will be sam-

pled again. The refresh cycle will continue until EXTNDRF is

sampled low on a positive edge of CLK.

The refresh address counter can be cleared by asserting

RFSH while DISRFSH is negated as shown in Figure 20a.

This can be used prior to a burst refresh of the entire memo-

ry array. By asserting RFSH one period of CLK before

DISRFSH is asserted and then keeping both inputs assert-

ed, the DP8420A/21A/22A will clear the refresh address

counter and then perform refresh cycles separated by the

programmed value of precharge as shown in Figure 20b. An

end-of-count signal can be generated from the Q DRAM

address outputs of the DP8420A/21A/22A and used to ne-

gate RFSH.

TL/F/8588–71

FIGURE 19. Extending Refresh with the Extend Refresh (EXTNDRF) Input

TL/F/8588–72

FIGURE 20a. Clearing the Refresh Address Counter

TL/F/8588–73

FIGURE 20b. Clearing the Refresh Counter during Burst

27

5.0 Refresh Options (Continued)

refresh request clock, the user is guaranteed that an inter-

nal refresh request will not be generated for approximately

15 ms, one refresh clock period, from the time RFSH is neg-

ated. This action will also clear the refresh address counter.

5.5 CLEARING THE REFRESH REQUEST CLOCK

The refresh request clock can be cleared by negating

DISRFSH and asserting RFSH for 500 ns, one period of the

internal 2 MHz clock as shown in Figure 21. By clearing the

TL/F/8588–75

FIGURE 21. Clearing the Refresh Request Clock Counter

6.0 Port A Wait State Support

Wait states allow a CPU’s access cycle to be increased by

one or multiple CPU clock periods. The wait or ready input is

named differently by CPU manufacturers. However, any

CPU’s wait or ready input is compatible with either the WAIT

or DTACK output of the DP8420A/21A/22A. The user de-

termines whether to program WAIT or DTACK (R7) and

which value to select for WAIT or DTACK (R2, R3) depend-

ing upon the CPU used and where the CPU samples its wait

input during an access cycle.

length of the CPU’s access. Once the event has been com-

pleted, the DP8420A/21A/22A will allow the access to take

place and stop inserting wait states.

There are six programming bits, R2–R7; an input, WAITIN;

and an output that functions as WAIT or DTACK.

6.1 WAIT TYPE OUTPUT

With the R7 address bit negated during programming, the

user selects the WAIT output. As long as WAIT is sampled

asserted by the CPU, wait states (extra clock periods) are

inserted into the current access cycle as shown in Figure

22. Once WAIT is sampled negated, the access cycle is

completed by the CPU. WAIT is asserted at the beginning of

a chip selected access and is programmed to negate a

number of positive edges and/or negative levels of CLK

from the event that starts the access. WAIT can also be

programmed to function in page/burst mode applications.

Once WAIT is negated during an access, and the ECAS

inputs are negated with AREQ asserted, WAIT can be pro-

grammed to toggle, following the ECAS inputs. Once AREQ

is negated, ending the access, WAIT will stay negated until

the next chip selected access. For more details about WAIT

Type Output, see Application Note AN-773.

The decision to terminate the CPU access cycle is directly

affected by the speed of the DRAMs used. The system de-

signer must ensure that the data from the DRAMs will be

present for the CPU to sample or that the data has been

written to the DRAM before allowing the CPU access cycle

to terminate.

The insertion of wait states also allows a CPU’s access cy-

cle to be extended until the DRAM access has taken place.

The DP8420A/21A/22A insert wait states into CPU access

cycles due to; guaranteeing precharge time, refresh current-

ly in progress, user programmed wait states, the WAITIN

signal being asserted and GRANTB not being valid

(DP8422A only). If one of these events is taking place and

the CPU starts an access, the DP8420A/21A/22A will insert

wait states into the access cycle, thereby increasing the

TL/F/8588–76

FIGURE 22. WAIT Type Output

28

6.0 Port A Wait State Support (Continued)

6.2 DTACK TYPE OUTPUT

6.3 DYNAMICALLY INCREASING THE

NUMBER OF WAIT STATES

With the R7 address bit asserted during programming, the

user selects the DTACK type output. As long as DTACK is

sampled negated by the CPU, wait states are inserted into

the current access cycle as shown in Figure 23. Once

DTACK is sampled asserted, the access cycle is completed

by the CPU. DTACK, which is normally negated, is pro-

grammed to assert a number of positive edges and/or neg-

ative levels from the event that starts RAS for the access.

DTACK can also be programmed to function during page/

burst mode accesses. Once DTACK is asserted and the

ECAS inputs are negated with AREQ asserted, DTACK can

be programmed to negate and assert from the ECAS inputs

toggling to perform a page/burst mode operation. Once

AREQ is negated, ending the access, DTACK will be negat-

ed and stays negated until the next chip selected access.

For more details about DTACK type output see Application

Note AN-773.

The user can increase the number of positive edges of CLK

before DTACK is asserted or WAIT is negated. With the

input WAITIN asserted, the user can delay DTACK asserting

or WAIT negating either one or two more positive edges of

CLK. The number of edges is programmed through address

bit R6. If the user is increasing the number of positive edges

in a delay that contains a negative level, the positive edges

will be met before the negative level. For example if the user

programmed DTACK of (/2T, asserting WAITIN, pro-

grammed as 2T, would increase the number of positive edg-

es resulting in DTACK of 2(/2T as shown inFigure 24a. Simi-

larly, WAITIN can increase the number of positive edges in

a page/burst access. WAITIN can be permanently asserted

in systems requiring an increased number of wait states.

WAITIN can also be asserted and negated, depending on

the type of access. As an example, a user could invert the

WRITE line from the CPU and connect the output to

WAITIN. This could be used to perform write accesses with

1 wait state and read accesses with 2 wait states as shown

in Figure 24b.

TL/F/8588–97

FIGURE 23. DTACK Type Output

TL/F/8588–C1

FIGURE 24a. WAITIN Example (DTACK is Sampled at the ‘‘T3’’ Falling Clock Edge)

29

6.0 Port A Wait State Support (Continued)

TL/F/8588–C2

FIGURE 24b. WAITIN Example (WAIT is Sampled at the End of ‘‘T2’’).

6.4 GUARANTEEING RAS LOW TIME

AND RAS PRECHARGE TIME

The DP8420A/21A/22A will guarantee RAS precharge time

between accesses; between refreshes; and between ac-

cess and refreshes. The programming bits R0 and R1 are

used to program combinations of RAS precharge time and

RAS low time referenced by positive edges of CLK. RAS

low time is programmed for refreshes only. During an ac-

cess, the system designer guarantees the time RAS is as-

serted through the DP8420A/21A/22A wait logic. Since in-

serting wait states into an access increases the length of

the CPU signals which are used to create ADS or ALE and

AREQ, the time that RAS is asserted can be guaranteed.

tive edge of CLK counter. AREQ is negated setup to a posi-

tive edge of CLK to terminate the access. That positive

edge is 1T. The next positive edge is 2T. RAS will not be

asserted until the programmed number of positive edges of

CLK have passed as shown in Figure 25. Once the pro-

grammed precharge time has been met, RAS will be assert-

ed from the positive edge of CLK. However, since there is a

precharge counter per RAS, an access using another RAS

will not be delayed. Precharge time before a refresh is al-

ways referenced from the access RAS negating before

RAS0 for the refresh asserting. After a refresh, precharge

time is referenced from RAS3 negating, for the refresh, to

the access RAS asserting.

The precharge time is also guaranteed by the

DP8420A/21A/22A. Each RAS output has a separate posi-

TL/F/8588–C3

FIGURE 25. Guaranteeing RAS Precharge (DTACK is Sampled at the ‘‘T2’’ Falling Clock Edge)

30

7.0 RAS and CAS Configuration Modes

The DP8420A/21A/22A allow the user to configure the

DRAM array to contain one, two or four banks of DRAM.

Depending on the functions used, certain considerations

must be used when determining how to set up the DRAM

array. Programming address bits C4, C5 and C6 along with

bank selects, B0–1, and CAS enables, ECAS0–3, deter-

mine which RAS or group of RASs and which CAS or group

of CASs will be asserted during an access. Different memo-

ry schemes are described. The DP8420A/21A/22A is spec-

ified driving a heavy load of 72 DRAMs, representing four

banks of DRAM with 16-bit words and 2 parity bits. The

DP8420A/21A/22A can drive more than 72 DRAMs, but the

AC timing must be increased. Since the RAS and CAS out-

puts are configurable, all RAS and CAS outputs should be

used for the maximum amount of drive.

7.1 BYTE WRITING

By selecting a configuration in which all CAS outputs are

selected during an access, the ECAS inputs enable a single

or group of CAS outputs to select a byte (or bytes) in a word

size of up to 32 bits. In this case, the RAS outputs are used

to select which of up to 4 banks is to be used as shown in

Figures 26a and 26b. In systems with a word size of 16 bits,

the byte enables can be gated with a high order address bit

to produce four byte enables which gives an equivalent to 8

banks of 16-bit words as shown inFigure 26d. If less memo-

ry is required, each CAS should be used to drive each nibble

in the 16-bit word as shown in Figure 26c.

TL/F/8588–C9

e

FIGURE 26a. DRAM Array Setup for 32-Bit System (C6, C5, C4

1, 1, 0 during Programming)

TL/F/8588–D0

e

0, 1, 1 No Error Scrubbing during Programming)

FIGURE 26b. DRAM Array Setup for 32-Bit, 1 Bank System (C6, C5, C4

e

0, 0, 0 Allowing Error Scrubbing

or C6, C5, C4

31

7.0 RAS and CAS Configuration Modes (Continued)

TL/F/8588–D1

e

FIGURE 26c. DRAM Array Setup for 16-Bit System (C6, C5, C4

1, 1, 0 during Programming)

TL/F/8588–D2

e

FIGURE 26d. 8 Bank DRAM Array for 16-Bit System (C6, C5, C4

1, 1, 0 during Programming)

32

7.0 RAS and CAS Configuration Modes (Continued)

7.2 MEMORY INTERLEAVING

7.3 ADDRESS PIPELINING

Memory interleaving allows the cycle time of DRAMs to be

reduced by having sequential accesses to different memory

banks. Since the DP8420A/21A/22A have separate pre-

charge counters per bank, sequential accesses will not be

delayed if the accessed banks use different RAS outputs.

To ensure different RAS outputs will be used, a mode is

selected where either one or two RAS outputs will be as-

serted during an access. The bank select or selects, B0 and

B1, are then tied to the least significant address bits, caus-

ing a different group of RASs to assert during each sequen-

tial access as shown in Figure 27. In this figure there should

be at least one clock period of all RAS’s negated between

different RAS’s being asserted to avoid the condition of a

CAS before RAS refresh cycle.

Address pipelining allows several access RASs to be as-

serted at once. Because RASs can overlap, each bank re-

quires either a mode where one RAS and one CAS are used

per bank as shown in Figure 28a or where two RASs and

two CASs are used per bank as shown in Figure 28b. Byte

writing can be accomplished in a 16-bit word system if two

RASs and two CASs are used per bank. In other systems,

WEs (or external gating on the CAS outputs) must be used

to perform byte writing. If WEs are used separate data in

and data out buffers must be used. If the array is not layed

out this way, a CAS to a bank can be low before RAS, which

will cause a refresh of the DRAM, not an access. To take

full advantage of address pipelining, memory interleaving is

used. To memory interleave, the least significant address

bits should be tied to the bank select inputs to ensure that

all ‘‘back to back’’ sequential accesses are not delayed,

since different memory banks are accessed.

TL/F/8588–D3

e

FIGURE 27. Memory Interleaving (C6, C5, C4

1, 1, 0 during Programming)

33

7.0 RAS and CAS Configuration Modes (Continued)

TL/F/8588–D4

e

FIGURE 28a. DRAM Array Setup for 4 Banks Using Address Pipelining (C6, C5, C4

e

1, 1, 1

or C6, C5, C4

0, 1, 0 (Also Allowing Error Scrubbing) during Programming)

TL/F/8588–D5

e

0, 0, 1 (Also Allowing Error Scrubbing) during Programming)

FIGURE 28b. DRAM Array Setup for Address Pipelining with 2 Banks (C6, C5, C4

e

1, 0, 1

or C6, C5, C4

7.4 ERROR SCRUBBING

In error scrubbing during refresh, the user selects one, two

or four RAS and CAS outputs per bank. When performing

error detection and correction, memory is always accessed

as words. Since the CAS signals are not used to select

individual bytes, the ECAS inputs can be tied low as shown

in Figures 29a and 29b.

TL/F/8588–D6

e

FIGURE 29a. DRAM Array Setup for 4 Banks Using Error Scrubbing (C6, C5, C4

0, 1, 0 during Programming)

TL/F/8588–D7

e

FIGURE 29b. DRAM Array Setup for Error Scrubbing with 2 Banks (C6, C5, C4

0, 0, 1 during Programming)

34

7.0 RAS and CAS Configuration Modes (Continued)

7.5 PAGE/BURST MODE

In a static column, page or burst mode system, the least

significant bits must be tied to the column address in order

to ensure that the page/burst accesses are to sequential

memory addresses, as shown in Figure 30. In a nibble

mode system, the least significant bits must be tied to the

highest column and row address bits in order to ensure that

sequential address bits are the ‘‘nibble’’ bits for nibble mode

accesses (Figure 30). The ECAS inputs may then be tog-

gled with the DP8420A/21A/22A’s address latches in fall-

through mode, while AREQ is asserted. The ECAS inputs

can also be used to select individual bytes. When using nib-

ble mode DRAMS, the third and fourth address bits can be

tied to the bank select inputs to perform memory interleav-

ing. In page or static column modes, the two address bits

after the page size can be tied to the bank select inputs to

select a new bank if the page size is exceeded.

TL/F/8588–D8

*See table below for row, column & bank address bit map. A0, A1 are used for byte addressing in this example.

Page Mode/Static Column Mode Page Size

Addresses

Nibble Mode*

256 Bits/Page 512 Bits/Page 1024 Bits/Page 2048 Bits/Page

e

A2–10 C0–9 A2–11

Column

Address

C9,R9

A2,A3 C0–7

A2–9 C0–8

e

C0–10

A2–12

e

C10 X

C0–8

X

C8–10

X

C9,10

X

Row

X

Address

B0

B1

A4

A5

A10

A11

A12

A13

A14

Assume that the least significant address bits are used for byte addressing. Given a 32-bit system A0,A1 would be

used for byte addressing.

e

X

DON’T CARE, the user can do as he pleases.

*Nibble mode values for R and C assume a system using 1 Mbit DRAMs.

FIGURE 30. Page, Static Column, Nibble Mode System

35

8.0 Test Mode

Staggered refresh in combination with the error scrubbing

mode places the DP8420A/21A/22A in test mode. In this

mode, the 24-bit refresh counter is divided into a 13-bit and

11-bit counter. During refreshes both counters are incre-

mented to reduce test time.

9.2 CALCULATION OF t

RAH

AND t

ASC

There are two clock inputs to the DP8420A/21A/22A.

These two clocks, DELCLK and CLK can either be tied to-

gether to the same clock or be tied to different clocks run-

ning asynchronously at different frequencies.

The clock input, DELCLK, controls the internal delay line

and refresh request clock. DELCLK should be a multiple of

9.0 DRAM Critical Timing

Parameters

The two critical timing parameters, shown in Figure 31, that

2 MHz. If DELCLK is not a multiple of 2 MHz, t

and t

ASC

and t

RAH ASC

can be calcu-

will change. The new values of t

lated by the following formulas:

RAH

must be met when controlling the access timing to a DRAM

, and the column ad-

RAH

are the row address hold time, t

dress setup time, t

e

was programmed to equal 15 ns then t

RAH

If t

RAH

30*(((DELCLK Divisor)* 2 MHz/(DELCLK Frequency)) 1)

. Since the DP8420A/21A/22A con-

ASC

b

tain a precise internal delay line, the values of these param-

eters can be selected at programming time. These values

will also increase and decrease if DELCLK varies from

2 MHz.

a

15 ns.

e

If t was programmed to equal 25 ns then t

RAH RAH

b

30*(((DELCLK Divisor)* 2 MHz/(DELCLK Frequency)) 1)

a

25 ns.

e

ASC

9.1 PROGRAMMABLE VALUES OF t

RAH

AND t

ASC

If t

ASC

was programmed to equal 0 ns then t

15*

15 ns.

b

((DELCLK Divisor)* 2 MHz/(DELCLK Frequency))

If t was programmed to equal 10 ns then t

The DP8420A/21A/22A allow the values of t

RAH

and t

ASC

e

25*

15 ns.

to be selected at programming time. For each parameter,

two choices can be selected. t , the row address hold

ASC

((DELCLK Divisor)* 2 MHz/(DELCLK Frequency))

ASC

b

RAH

time, is measured from RAS asserted to the row address

starting to change to the column address. The two choices

Since the values of t and t

RAH

are increased or de-

ASC

creased, the time to CAS asserted will also increase or de-

crease. These parameters can be adjusted by the following

formula:

for t

are 15 ns and 25 ns, programmable through ad-

RAH

dress bit C8.

t

, the column address setup time, is measured from the

ASC

e

a

b

Actual t

RAH

Delay to CAS

Programmed t

Actual Spec.

a

column address valid to CAS asserted. The two choices for

are 0 ns and 10 ns, programmable through address bit

b

Actual t

Programmed t

.

ASC

RAH

ASC

t

ASC

C7.

TL/F/8588–E3

FIGURE 31. t

RAH

and t

ASC

36

10.0 Dual Accessing (DP8422A)

The DP8422A has all the functions previously described. In

addition to those features, the DP8422A also has the capa-

bilities to arbitrate among refresh, Port A and a second port,

Port B. This allows two CPUs to access a common DRAM

array. DRAM refresh has the highest priority followed by the

currently granted port. The ungranted port has the lowest

priority. The last granted port will continue to stay granted

even after the access has terminated, until an access re-

quest is received from the ungranted port (see Figure 32a ).

The dual access configuration assumes that both Port A

and Port B are synchronous to the system clock. If they are

not synchronous to the system clock they should be exter-

nally synchronized (Ex. By running the access requests

through several Flip-Flops, see Figure 34a ).

has completed. It is important to note that for GRANTB to

transition to Port B, Port A must not be requesting an ac-

cess at a rising clock edge (or locked) and Port B must be

requesting an access at that rising clock edge. Port A can

request an access through CS and ADS/ALE or CS and

AREQ. Therefore during an interleaved access where CS

and ADS/ALE become asserted before AREQ from the pre-

e

vious access is negated, Port A will retain GRANTB

whether AREQB is asserted or not.

0

Since there is no chip select for Port B, AREQB must incor-

porate this signal. This mode of accessing is similar to Mode

1 accessing for Port A.

10.1 PORT B ACCESS MODE

Port B accesses are initiated from a single input, AREQB.

When AREQB is asserted, an access request is generated.

If GRANTB is asserted and a refresh is not taking place or

precharge time is not required, RAS will be asserted when

AREQB is asserted. Once AREQB is asserted, it must stay

asserted until the access is over. AREQB negated, negates

TL/F/8588–F9

Explanation of Terms

e

RAS as shown inFigure 32b. Note that if ECAS0

1 during

e

AREQA

AREQB

Chip Selected access request from Port A

Chip Selected access request from Port B

programming the CAS outputs may be held asserted (be-

yond RASn negating) by continuing to assert the appropri-

ate ECASn inputs (the same as Port A accesses). If Port B

is not granted, the access will begin on the first or second

positive edge of CLK after GRANTB is asserted (See R0,

R1 programming bit definitions) as shown in Figure 32c, as-

suming that Port A is not accessing the DRAM (CS, ADS/

ALE and AREQ) and RAS precharge for the particular bank

e

LOCK

Externally controlled LOCKing of the Port

that is currently GRANTed.

FIGURE 32a. DP8422A Port A/Port B Arbitration

State Diagram. This arbitration may take place

during the ‘‘ACCESS’’ or ‘‘REFRESH’’

state (seeFigure 13a ).

TL/F/8588–E4

FIGURE 32b. Access Request for Port B

TL/F/8588–E5

FIGURE 32c. Delayed Port B Access

37

10.0 Dual Accessing (DP8422A) (Continued)

10.2 PORT B WAIT STATE SUPPORT

Port A or Port B to lock out the other port from the DRAM.

When a Port is locked out of the DRAM, wait states will be

inserted into its access cycle until it is allowed to access

memory. GRANTB is used to multiplex the input control sig-

nals and addresses to the DP8422A.

Advanced transfer acknowledge for Port B, ATACKB, is

used for wait state support for Port B. This output will be

asserted when RAS for the Port B access is asserted, as

shown in Figures 33a and 33b. Once asserted, this output

will stay asserted until AREQB is negated. With external

logic, ATACKB can be made to interface to any CPU’s wait

input as shown in Figure 33c.

10.3.1 GRANTB Output

The output GRANTB determines which port has current ac-

cess to the DRAM array. GRANTB asserted signifies Port B

has access. GRANTB negated signifies Port A has access

to the DRAM array.

10.3 COMMON PORT A AND PORT B DUAL PORT

FUNCTIONS

An input, LOCK, and an output, GRANTB, add additional

functionality to the dual port arbitration logic. LOCK allows

TL/F/8588–E6

FIGURE 33a. Non-Delayed Port B Access

TL/F/8588–E7

FIGURE 33b. Delayed Port B Access

TL/F/8588–31

B. Extend ATACK to 1T after RAS goes low.

TL/F/8588–30

A. Extend ATACK to (/2T ((/2 Clock) after RAS goes low.

TL/F/8588–32

C. Synchronize ATACKB to CPU B Clock. This is useful if CPU B runs asynchronous to the DP8422.

FIGURE 33c. Modifying Wait Logic for Port B

38

10.0 Dual Accessing (DP8422A) (Continued)

Since the DP8422A has only one set of address inputs, the

signal is used, with the addition of buffers, to allow the cur-

rently granted port’s addresses to reach the DP8422A. The

signals which need to be bufferred are R0–10, C0–10,

B0–1, ECAS0–3, WE, and LOCK. All other inputs are not

common and do not have to be buffered as shown in Figure

34a. If a Port, which is not currently granted, tries to access

the DRAM array, the GRANTB output will transition from a

rising clock edge from AREQ or AREQB negating and will

precede the RAS for the access by one or two clock peri-

ods. GRANTB will then stay in this state until the other port

requests an access and the currently granted port is not

accessing the DRAM as shown in Figure 34b.

TL/F/8588–55

*If Port B is synchronous the Request Synchronizing logic will not be required.

FIGURE 34a. Dual Accessing with the DP8422A (System Block Diagram)

39

10.0 Dual Accessing (DP8422A) (Continued)

TL/F/8588–29

FIGURE 34b. Wait States during a Port B Access

10.3.2 LOCK Input

When the LOCK input is asserted, the currently granted port

can ‘‘lock out’’ the other port through the insertion of wait

states to that port’s access cycle. LOCK does not disable

refreshes, it only keeps GRANTB in the same state even if

the other port requests an access, as shown in Figure 35a.

LOCK can be used by either port.

TL/F/8588–E8

FIGURE 35. LOCK Function

40

11.0 Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

All Input or Output Voltage

b

a

with Respect to GNDÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ 0.5V to 7V

@

Power Dissipation 20 MHzÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ0.5W

a

Temperature under Bias ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ0 C to 70 C

§

Storage Temperature ÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀÀ 65 C to 150 C

§

ESD Rating to be determined.

b

a

§

e

a

0 C to 70 C, V

e

5V 10%, GND 0V

g

12.0 DC Electrical Characteristics T

§

A

CC

Symbol

Parameter

Conditions

Min

Typ

Max

Units

V

Logical 1 Input Voltage

Tested with a Limited

Functional Pattern

IH

a

2.0

V

CC

0.5

V

Logical 0 Input Voltage

Tested with a Limited

Functional Pattern

IL

b

0.5

0.8

0.5

V

e b

b

V

OH1

V

OL1

V

OH2

V

OL2

Q and WE Outputs

All Outputs except Qs, WE

Input Leakage Current

ML Input Current (Low)

Standby Current

I

10 mA

V

1.0

V

OH

OL

OH

OL

CC

e

10 mA

e b

3 mA

V

CC

e

3 mA

or GND

0.5

10

V

b

I

V

10

mA

IN

CC

GND

V

200

15

IL ML

CC1

CC2

e

CLK at 8 MHz (V

IN

V

or GND)

6

8

CC

e

Standby Current

CLK at 20 MHz (V

CLK at 25 MHz (V

V

or GND)

17

IN

CC

e

Standby Current

10

20

Supply Current

CLK at 8 MHz (Inputs Active)

e

V

20

40

50

40

75

mA

e

(I

LOAD

0) (V

IN

or GND)

CC

I

Supply Current

Input Capacitance

CLK at 20 MHz (Inputs Active)

e

V

CC2

e

(I

LOAD

0) (V

IN

or GND)

CC

CLK at 25 MHz (Inputs Active)

95

10

mA

pF

e

V

(I

f

0) (V

IN

or GND)

CC

LOAD

C

*

at 1 MHz

IN

*C is not 100% tested.

IN

41

13.0 AC Timing Parameters

Two speed selections are given, the DP8420A/21A/22A-20

and the DP8420A/21A/22A-25. The differences between

the two parts are the maximum operating frequencies of the

input CLKs and the maximum delay specifications. Low fre-

b

quency applications may use the ‘‘ 25’’ part to gain im-

proved timing.

300–315 Mode 0 access parameters used in both single

and dual access applications

400–416 Mode 1 access parameters used in both single

and dual access applications

450–455 Special Mode 1 access parameters which super-

sede the 400–416 parameters when dual ac-

cessing

The AC timing parameters are grouped into sectional num-

bers as shown below. These numbers also refer to the tim-

ing diagrams.

500–506 Programming parameters

k

T

A

k

e

g

Unless otherwise stated V

CC

5.0V 10%, 0

1–36

Common parameters to all modes of operation

Difference parameters used to calculate;

RAS low time,

70 C, the output load capacitance is typical for 4 banks of

§

50–56

18 DRAMs per bank, including trace capacitance (see Note

2).

RAS precharge time,

Two different loads are specified:

CAS high time and

e

C

50 pF loads on all outputs except

L

CAS low time

150 pF loads on Q0–8, 9, 10 and WE; or

50 pF loads on all outputs except

L

100–121 Common dual access parameters used for Port

B accesses and inputs and outputs used only in

dual accessing

H

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

200–212 Refresh parameters

Note 1: ‘‘Absolute Maximum Ratings’’ are the values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the device

should be operated at these limits. The table of ‘‘Electrical Characteristics’’ provides conditions for actual device operation.

e

2.5 ns. Input reference point on AC measurements is 1.5V. Output reference points are 2.4V for High and 0.8V for Low.

Note 2: Input pulse 0V to 3V; tR

tF

Note 3: AC Production testing is done at 50 pF.

TL/F/8588–E9

FIGURE 36. Clock, DELCLK Timing

42

13.0 AC Timing Parameters (Continued)

k

e

per bank, including trace capacitance (Note 2).

g

5.0V 10%, 0 C

Unless otherwise stated V

CC

T

70 C, the output load capacitance is typical for 4 banks of 18 DRAMs

§

A

e

Two different loads are specified:

C

H

C

H

C

H

50 pF loads on all outputs except

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

e

C

50 pF loads on all outputs except

150 pF loads on Q0–8, 9, 10 and WE; or

L

8420A/21A/22A-20

8420A/21A/22A-25

Common Parameter

Description

Number

Symbol

C

L

C

L

C

H

Min

0

Max

Min

0

Max

Min

0

Max

Min

0

Max

1

f

CLK Frequency

20

25

CLK

2

tCLKP

CLK Period

50

15

5

50

15

5

40

12

5

40

12

5

3, 4

5

tCLKPW

fDCLK

CLK Pulse Width

DELCLK Frequency

DELCLK Period

DELCLK Pulse Width

20

6

tDCLKP

tDCLKPW

50

15

200

50

15

200

50

12

200

50

12

200

7, 8

9a

tPRASCAS0 RAS Asserted to CAS Asserted

e

0 ns)

30

40

50

30

40

50

30

40

50

30

40

50

e

(tRAH

15 ns, tASC

9b

9c

9d

tPRASCAS1 RAS Asserted to CAS Asserted

e

10 ns)

e

(tRAH

15 ns, tASC

tPRASCAS2 (RAS Asserted to CAS Asserted

e

0 ns)

e

(tRAH

25 ns, tASC

tPRASCAS3 (RAS Asserted to CAS Asserted

e

10 ns)

e

(tRAH

25 ns, tASC

e

10a

10b

11a

11b

12

tRAH

Row Address Hold Time (tRAH

15)

25)

15

25

0

15

25

0

15

25

0

15

25

0

tRAH

e

tASC

Column Address Setup Time (tASC

0)

tASC

10)

10

tPCKRAS

CLK High to RAS Asserted

following Precharge

27

32

22

26

13

14

15

16

17

18

tPARQRAS AREQ Negated to RAS Negated

38

23

25

60

39

43

31

33

68

39

31

20

47

31

35

27

54

31

tPENCL

tPENCH

ECAS0–3 Asserted to CAS Asserted

ECAS0–3 Negated to CAS Negated

tPARQCAS AREQ Negated to CAS Negated

tPCLKWH

tPCLKDL0

CLK to WAIT Negated

CLK to DTACK Asserted

(Programmed as DTACK of 1/2, 1, 1(/2

or if WAITIN is Asserted)

33

44

33

44

28

36

28

36

19

20

tPEWL

tSECK

ECAS Negated to WAIT Asserted

during a Burst Access

ECAS Asserted Setup to CLK High to

Recognize the Rising Edge of CLK

during a Burst Access

24

19

43

13.0 AC Timing Parameters (Continued)

k

70 C, the output load capacitance is typical for 4 banks of 18 DRAMs

e

per bank, including trace capacitance (Note 2).

g

5.0V 10%, 0 C

Unless otherwise stated V

CC

T

A

§

e

Two different loads are specified:

C

H

C

H

C

H

50 pF loads on all outputs except

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

e

C

50 pF loads on all outputs except

150 pF loads on Q0–8, 9, 10 and WE; or

L

8420A/21A/22A-20

8420A/21A/22A-25

Common Parameter

Description

Number

Symbol

C

L

C

L

C

H

Min

Max

Min

Max

Min

Max

Min

Max

21

tPEDL

ECAS Asserted to DTACK

Asserted during a Burst Access

(Programmed as DTACK0)

48

38

22

tPEDH

tSWCK

ECAS Negated to DTACK

49

38

Negated during a Burst Access

23

24

25

26

WAITIN Asserted Setup to CLK

5

tPWINWEH WIN Asserted to WE Asserted

tPWINWEL WIN Negated to WE Negated

34

44

27

37

tPAQ

Row, Column Address Valid to

Q0–8, 9, 10 Valid

29

34

38

43

26

30

35

39

27

tPCINCQ

tSCINEN

COLINC Asserted to Q0–8, 9, 10

Incremented

28

COLINC Asserted Setup to ECAS

e

18

46

19

46

19

17

37

15

19

37

15

Asserted to Ensure tASC

0 ns

29a

29b

tSARQCK1 AREQ, AREQB Negated Setup to CLK

High with 1 Period of Precharge

tSARQCK2 AREQ, AREQB Negated Setup to CLK High

l

with 1 Period of Precharge Programmed

30

31

tPAREQDH AREQ Negated to DTACK Negated

34

31

34

39

27

25

27

32

tPCKCAS

CLK High to CAS Asserted

when Delayed by WIN

32

tSCADEN

Column Address Setup to ECAS

e

14

20

15

20

14

20

16

20

Asserted to Guarantee tASC

0

33

tWCINC

COLINC Pulse Width

34a

tPCKCL0

CLK High to CAS Asserted following

e

81

91

89

99

72

82

92

79

89

99

e

0 ns)

Precharge (tRAH

15 ns, tASC

34b

34c

34d

35

tPCKCL1

tPCKCL2

tPCKCL3

tCAH

CLK High to CAS Asserted following

e

Precharge (tRAH

15 ns, tASC

10 ns)

0 ns)

CLK High to CAS Asserted following

91

99

e

25 ns, tASC

Precharge (tRAH

CLK High to CAS Asserted following

e

101

109

e

10 ns)

Precharge (tRAH

25 ns, tASC

Column Address Hold Time

(Interleave Mode Only)

32

36

tPCQR

CAS Asserted to Row Address

Valid (Interleave Mode Only)

90

44

13.0 AC Timing Parameters (Continued)

k

70 C, the output load capacitance is typical for 4 banks of 18 DRAMs

e

per bank, including trace capacitance (Note 2).

g

5.0V 10%, 0 C

Unless otherwise stated V

CC

T

§

A

e

Two different loads are specified:

C

H

C

H

C

H

50 pF loads on all outputs except

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

e

C

50 pF loads on all outputs except

150 pF loads on Q0–8, 9, 10 and WE; or

L

8420A/21A/22A-20

8420A/21A/22A-25

Difference

Number Symbol

C

L

C

H

L

Parameter Description

Min

Max

Min

Max

Min

Max

Min

Max

50

tD1

(AREQ or AREQB Negated to RAS

Negated) Minus (CLK High to RAS

Asserted)

16

14

51

52

tD2

(CLK High to Refresh RAS Negated)

Minus (CLK High to RAS Asserted)

13

4

13

4

11

4

11

4

tD3a

(ADS Asserted to RAS Asserted

(Mode 1)) Minus (AREQ Negated

to RAS Negated)

53

54

55

56

tD3b

tD4

tD5

tD6

(CLK High to RAS Asserted (Mode 0))

Minus (AREQ Negated to RAS Negated)

4

7

6

4

7

6

4

7

6

4

7

6

(ECAS Asserted to CAS Asserted)

b

7

Minus (ECAS Negated to CAS Negated)

(CLK to Refresh RAS Asserted) Minus

(CLK to Refresh RAS Negated)

(AREQ Negated to RAS Negated)

Minus (ADS Asserted to RAS

Asserted (Mode 1))

12

10

45

13.0 AC Timing Parameters (Continued)

k

70 C, the output load capacitance is typical for 4 banks of 18 DRAMs

e

per bank, including trace capacitance (Note 2).

g

5.0V 10%, 0 C

Unless otherwise stated V

CC

T

A

§

e

Two different loads are specified:

C

H

C

H

C

H

50 pF loads on all outputs except

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

e

C

50 pF loads on all outputs except

150 pF loads on Q0–8, 9, 10 and WE; or

L

8420A/21A/22A-20

8420A/21A/22A-25

Common Dual Access

Parameter Description

Number

Symbol

C

L

C

H

L

Min

3

Max

Min

3

Max

Min

3

Max

Min

3

Max

100

101

102

103

105

tHCKARQB

tSARQBCK

tPAQBRASL

AREQB Negated Held from CLK High

AREQB Asserted Setup to CLK High

AREQB Asserted to RAS Asserted

8

7

43

41

48

46

37

32

41

36

tPAQBRASH AREQB Negated to RAS Negated

tPCKRASG

CLK High to RAS Asserted for

Pending Port B Access

55

57

67

60

57

67

44

45

51

48

45

51

106

107

tPAQBATKBL AREQB Asserted to ATACKB Asserted

tPCKATKB

CLK High to ATACKB Asserted

for Pending Access

108

109

110

tPCKGH

CLK High to GRANTB Asserted

CLK High to GRANTB Negated

40

35

40

35

32

29

32

29

tPCKGL

tSADDCKG

Row Address Setup to CLK High That

Asserts RAS following a GRANTB

11

5

15

5

11

5

16

5

e

Change to Ensure tASR

0 ns for Port B

111

tSLOCKCK

LOCK Asserted Setup to CLK Low

to Lock Current Port

112

113

114

tPAQATKBH AREQ Negated to ATACKB Negated

tPAQBCASH AREQB Negated to CAS Negated

26

59

26

67

21

47

21

54

tSADAQB

Address Valid Setup to

AREQB Asserted

7

5

11

5

7

5

12

5

116

117

tHCKARQG

tWAQB

AREQ Negated Held from CLK High

AREQB High Pulse Width

e

31

35

26

31

to Guarantee tASR

0 ns

118a

118b

118c

118d

120a

tPAQBCAS0

tPAQBCAS1

tPAQBCAS2

tPAQBCAS3

tPCKCASG0

AREQB Asserted to CAS Asserted

e

0 ns)

103

113

123

111

121

131

87

97

94

e

(tRAH

15 ns, tASC

AREQB Asserted to CAS Asserted

e

10 ns)

104

114

e

(tRAH

15 ns, tASC

AREQB Asserted to CAS Asserted

e

0 ns)

97

e

(tRAH

25 ns, tASC

AREQB Asserted to CAS Asserted

e

10 ns)

107

e

(tRAH

25 ns, tASC

CLK High to CAS Asserted

for Pending Port B Access

113

123

133

121

131

141

96

103

113

123

e

0 ns)

(tRAH

15 ns, tASC

120b

120c

120d

121

tPCKCASG1

tPCKCASG2

tPCKCASG3

CLK High to CAS Asserted

for Pending Port B Access

106

116

e

10 ns)

(tRAH

15 ns, tASC

CLK High to CAS Asserted

for Pending Port B Access

e

0 ns)

(tRAH

25 ns, tASC

CLK High to CAS Asserted

for Pending Port B Access

e

10 ns)

(tRAH

25 ns, tASC

tSBADDCKG Bank Address Valid Setup to CLK

High That Starts RAS

for Pending Port B Access

10

46

13.0 AC Timing Parameters (Continued)

TL/F/8588–F0

FIGURE 37. 100: Dual Access Port B

TL/F/8588–F1

FIGURE 38. 100: Port A and Port B Dual Access

47

13.0 AC Timing Parameters (Continued)

k

70 C, the output load capacitance is typical for 4 banks of 18 DRAMs

e

per bank, including trace capacitance (Note 2).

g

5.0V 10%, 0 C

Unless otherwise stated V

CC

T

A

§

e

Two different loads are specified:

C

H

C

H

C

H

50 pF loads on all outputs except

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

e

C

50 pF loads on all outputs except

150 pF loads on Q0–8, 9, 10 and WE; or

L

8420A/21A/22A-20

8420A/21A/22A-25

Refresh Parameter

Description

Number

Symbol

C

L

C

H

L

Min

27

Max

Min

27

Max

Min

22

Max

Min

22

Max

200

201

202

204

205

206

207

208

209a

tSRFCK

RFSH Asserted Setup to CLK High

DISRFSH Asserted Setup to CLK High

EXTENDRF Setup to CLK High

CLK High to RFIP Asserted

tSDRFCK

tSXRFCK

tPCKRFL

tPARQRF

tPCKRFH

28

22

15

12

39

62

65

35

28

39

62

65

40

33

31

50

51

29

23

31

50

51

33

27

AREQ Negated to RFIP Asserted

CLK High to RFIP Negated

tPCKRFRASH CLK High to Refresh RAS Negated

tPCKRFRASL CLK High to Refresh RAS Asserted

tPCKCL0

tPCKCL1

tPCKCL2

tPCKCL3

CLK High to CAS Asserted

during Error Scrubbing

82

92

90

73

83

93

80

90

e

0 ns)

(t

15 ns, t

ASC

RAH

209b

209c

209d

CLK High to CAS Asserted

during Error Scrubbing

100

110

e

10 ns)

(t

RAH

15 ns, t

ASC

CLK High to CAS Asserted

during Error Scrubbing

92

90

e

0 ns)

(t

25 ns, t

ASC

RAH

CLK High to CAS Asserted

during Error Scrubbing

102

100

e

10 ns)

(t

25 ns, t

ASC

RAH

210

211

212

tWRFSH

tPCKRQL

tPCKRQH

RFSH Pulse Width

15

CLK High to RFRQ Asserted

CLK High to RFRQ Negated

46

50

46

50

40

TL/F/8588–F2

FIGURE 39. 200: Refresh Timing

48

13.0 AC Timing Parameters (Continued)

k

70 C, the output load capacitance is typical for 4 banks of 18 DRAMs

e

per bank, including trace capacitance (Note 2).

g

5.0V 10%, 0 C

Unless otherwise stated V

CC

T

§

A

e

Two different loads are specified:

C

H

C

H

C

H

50 pF loads on all outputs except

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

e

C

50 pF loads on all outputs except

150 pF loads on Q0–8, 9, 10 and WE; or

L

8420A/21A/22A-20

8420A/21A/22A-25

Mode 0 Access

Parameter Description

Number

Symbol

C

L

C

H

C

L

C

H

Min

Max

Min

Max

Min

Max

Min

Max

300

tSCSCK

CS Asserted to CLK High

14

13

301a

tSALECKNL ALE Asserted Setup to CLK High

Not Using On-Chip Latches or

if Using On-Chip Latches and

16

29

16

29

15

29

15

29

B0, B1, Are Constant, Only 1 Bank

301b

tSALECKL

ALE Asserted Setup to CLK High,

if Using On-Chip Latches if B0, B1

Can Change, More Than One Bank

302

303

304

tWALE

ALE Pulse Width

18

20

18

20

13

18

13

18

tSBADDCK

tSADDCK

Bank Address Valid Setup to CLK High

Row, Column Valid Setup to

CLK High to Guarantee

11

10

3

15

10

3

11

8

16

8

e

tASR

0 ns

305

306

tHASRCB

tSRCBAS

Row, Column, Bank Address

Held from ALE Negated

(Using On-Chip Latches)

Row, Column, Bank Address

Setup to ALE Negated

(Using On-Chip Latches)

2

307

tPCKRL

CLK High to RAS Asserted

27

81

32

89

22

72

26

79

308a

tPCKCL0

CLK High to CAS Asserted

e

(t

RAH

15 ns, t

0 ns)

ASC

308b

308c

308d

tPCKCL1

tPCKCL2

tPCKCL3

CLK High to CAS Asserted

e

91

99

82

92

89

99

e

(t

RAH

15 ns, t

10 ns)

ASC

CLK High to CAS Asserted

e

(t

RAH

25 ns, t

0 ns)

ASC

CLK High to CAS Asserted

e

101

109

e

10 ns)

(t

RAH

25 ns, t

ASC

309

310

tHCKALE

tSWINCK

ALE Negated Hold from CLK High

0

WIN Asserted Setup to CLK High

to Guarantee CAS is Delayed

b

16

21

16

311

312

313

tPCSWL

tPCSWH

tPCLKDL1

CS Asserted to WAIT Asserted

CS Negated to WAIT Negated

26

30

26

30

22

25

22

25

CLK High to DTACK Asserted

(Programmed as DTACK0)

40

35

40

35

32

29

32

29

314

315

tPALEWL

ALE Asserted to WAIT Asserted

(CS is Already Asserted)

AREQ Negated to CLK High That Starts

e

Access RAS to Guarantee tASR

(Non-Interleaved Mode Only)

0 ns

41

45

34

39

316

tPCKCV0

CLK High to Column

Address Valid

78

87

66

75

e

0 ns)

(t

15 ns, t

ASC

RAH

49

13.0 AC Timing Parameters (Continued)

TL/F/8588–F3

FIGURE 40. 300: Mode 0 Timing

50

13.0 AC Timing Parameters (Continued)

TL/F/8588–F4

e

1, C6 1)

(Programmed as C4

1, C5

FIGURE 41. 300: Mode 0 Interleaving

51

13.0 AC Timing Parameters (Continued)

k

70 C, the output load capacitance is typical for 4 banks of 18 DRAMs

e

per bank, including trace capacitance (Note 2).

g

5.0V 10%, 0 C

Unless otherwise stated V

CC

T

A

§

e

Two different loads are specified:

C

H

C

H

C

H

50 pF loads on all outputs except

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

e

C

50 pF loads on all outputs except

150 pF loads on Q0–8, 9, 10 and WE; or

L

8420A/21A/22A-20

8420A/21A/22A-25

Mode 1 Access

Parameter Description

Number

Symbol

C

L

C

H

L

Min

Max

Min

Max

Min

Max

Min

Max

400a

400b

tSADSCK1 ADS Asserted Setup to CLK High

15

31

6

15

13

tSADSCKW ADS Asserted Setup to CLK

(to Guarantee Correct WAIT

31

6

25

5

25

5

or DTACK Output; Doesn’t Apply for DTACK0)

401

tSCSADS

tPADSRL

tPADSCL0

CS Setup to ADS Asserted

402

ADS Asserted to RAS Asserted

ADS Asserted to CAS Asserted

30

86

35

94

25

75

29

82

403a

e

0 ns)

(tRAH

15 ns, tASC

403b

403c

403d

404

tPADSCL1

tPADSCL2

tPADSCL3

ADS Asserted to CAS Asserted

e

10 ns)

96

104

114

85

95

92

e

(tRAH

15 ns, tASC

ADS Asserted to CAS Asserted

e

0 ns)

e

(tRAH

25 ns, tASC

ADS Asserted to CAS Asserted

e

10 ns)

106

102

e

(tRAH

25 ns, tASC

tSADDADS Row Address Valid Setup to ADS

e

9

0

13

0

9

0

14

0

Asserted to Guarantee tASR

0 ns

405

406

tHCKADS

tSWADS

ADS Negated Held from CLK High

WAITIN Asserted Setup to ADS

Asserted to Guarantee DTACK0

Is Delayed

0

407

408

tSBADAS

tHASRCB

Bank Address Setup to ADS Asserted

11

10

11

10

11

10

11

10

Row, Column, Bank Address Held from

ADS Asserted (Using On-Chip Latches)

409

tSRCBAS

Row, Column, Bank Address Setup to

ADS Asserted (Using On-Chip Latches)

3

2

410

411

tWADSH

tPADSD

ADS Negated Pulse Width

12

16

12

17

ADS Asserted to DTACK Asserted

(Programmed as DTACK0)

43

35

412

tSWINADS WIN Asserted Setup to ADS Asserted

(to Guarantee CAS Delayed during

Writes Accesses)

b

10

413

414

415

tPADSWL0 ADS Asserted to WAIT Asserted

(Programmed as WAIT0, Delayed Access)

35

29

tPADSWL1 ADS Asserted to WAIT Asserted

(Programmed WAIT 1/2 or 1)

tPCLKDL1

CLK High to DTACK Asserted

(Programmed as DTACK0,

Delayed Access)

40

32

416

417

AREQ Negated to ADS Asserted

e

(Non Interleaved Mode Only)

to Guarantee tASR

0 ns

38

42

31

36

tPADSCV0 ADS Asserted to Column

Address Valid

83

92

69

78

e

0 ns)

(t

15 ns, t

ASC

RAH

52

13.0 AC Timing Parameters (Continued)

TL/F/8588–F5

FIGURE 42. 400: Mode 1 Timing

53

13.0 AC Timing Parameters (Continued)

TL/F/8588–F6

FIGURE 43. 400: COLINC Page/Static Column Access Timing

54

13.0 AC Timing Parameters (Continued)

k

70 C, the output load capacitance is typical for 4 banks of 18 DRAMs

e

per bank, including trace capacitance (Note 2).

g

5.0V 10%, 0 C

Unless otherwise stated V

CC

T

§

A

e

Two different loads are specified:

C

H

C

H

C

H

50 pF loads on all outputs except

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

e

C

50 pF loads on all outputs except

150 pF loads on Q0–8, 9, 10 and WE; or

L

8420A/21A/22A-20

8420A/21A/22A-25

Mode 1 Dual Access

Number

Symbol

C

L

C

H

L

Parameter Description

Min

Max

Min

Max

Min

Max

Min

Max

450

tSADDCKG

Row Address Setup to CLK High That

Asserts RAS following a GRANTB

11

15

11

16

e

Port Change to Ensure tASR

0 ns

451

tPCKRASG

tPCLKDL2

tPCKCASG0

CLK High to RAS Asserted

for Pending Access

48

53

38

43

42

43

452

CLK to DTACK Asserted for Delayed

Accesses (Programmed as DTACK0)

453a

CLK High to CAS Asserted

for Pending Access

101

111

121

109

119

129

86

96

93

e

0 ns)

(t

15 ns, t

ASC

RAH

453b

453c

453d

tPCKCASG1

tPCKCASG2

tPCKCASG3

CLK High to CAS Asserted

for Pending Access

103

113

e

10 ns)

(t

15 ns, t

ASC

RAH

CLK High to CAS Asserted

for Pending Access

96

e

0 ns)

(t

RAH

25 ns, t

ASC

CLK High to CAS Asserted

for Pending Access

106

e

10 ns)

(t

25 ns, t

ASC

RAH

454

455

tSBADDCKG Bank Address Valid Setup to CLK High

that Asserts RAS for Pending Access

5

4

tSADSCK0

ADS Asserted Setup to CLK High

12

11

55

13.0 AC Timing Parameters (Continued)

k

DRAMs per bank, including trace capacitance (Note 2).

k

70 C, the output load capacitance is typical for 4 banks of 18

e

g

5.0V 10%, 0 C

Unless otherwise stated V

T

A

§

CC

e

Two different loads are specified:

C

H

C

H

C

H

50 pF loads on all outputs except

125 pF loads on RAS0–3 and CAS0–3 and

380 pF loads on Q0–8, 9, 10 and WE.

e

C

50 pF loads on all outputs except

150 pF loads on Q0–8, 9, 10 and WE; or

L

8420A/21A/22A-20

8420A/21A/22A-25

Programming

Number

Symbol

C

L

C

H

C

L

C

H

Parameter Description

Min Max Min Max Min Max Min Max

500

501

502

503

504

505

tHMLADD

tSADDML

tWML

Mode Address Held from ML Negated

Mode Address Setup to ML Negated

ML Pulse Width

8

6

8

6

7

6

7

6

15

0

15

0

15

0

15

0

tSADAQML Mode Address Setup to AREQ Asserted

tHADAQML Mode Address Held from AREQ Asserted

51

38

tSCSARQ

CS Asserted Setup to

AREQ Asserted

6

506

tSMLARQ

ML Asserted Setup to AREQ Asserted

10

TL/F/8588–F7

FIGURE 44. 500: Programming

56

wrap board) because they may be needed. The value of

these damping resistors (if needed) will vary depending

upon the output, the capacitance of the load, and the

characteristics of the trace as well as the routing of the

trace. The value of the damping resistor also may vary

between the wire-wrap board and the printed circuit

board. To determine the value of the series damping re-

sistor it is recommended to use an oscilloscope and look

at the furthest DRAM from the DP8420A/21A/22A. The

undershoot of RAS, CAS, WE and the addresses should

be kept to less than 0.5V below ground by varying the

value of the damping resistor. The damping resistors

should be placed as close as possible with short leads to

the driver outputs of the DP8420A/21A/22A.

14.0 Functional Differences

between the DP8420A/21A/22A

and the DP8420/21/22

1. Extending the Column Address Strobe (CAS) after

AREQ Transitions High

The DP8420A/21A/22A allows CAS to be asserted for

an indefinite period of time beyond AREQ (or AREQB,

DP8422A only. Scrubbing refreshes are not affected.) be-

ing negated by continuing to assert the appropriate ECAS

inputs. This feature is allowed as long as the ECAS0 input

was negated during programming. The DP8420/21/22

does not allow this feature.

2. Dual Accessing

5. The circuit board must have a good V

and ground

CC

plane connection. If the board is wire-wrapped, the V

The DP8420A/21A/22A asserts RAS either one or two

clock periods after GRANTB has been asserted or negat-

ed depending upon how the R0 bit was programmed dur-

ing the mode load operation. The DP8420/21/22 will al-

ways start RAS one clock period after GRANTB is assert-

ed or negated. The above statements assume that RAS

precharge has been completed by the time GRANTB is

asserted or negated.

CC

and ground pins of the DP8420A/21A/22A, the DRAM

associated logic and buffer circuitry must be soldered to

the V

and ground planes.

CC

6. The traces from the DP8420A/21A/22A to the DRAM

should be as short as possible.

7. ECAS0 should be held low during programming if the user

wishes that the DP8420A/21A/22A be compatible with a

DP8420/21/22 design.

3. Refresh Request Output (RFRQ)

The DP8420A/21A/22A allows RFRQ (refresh request)

to be output on the WE output pin given that ECAS0 was

negated during programming or the controller was pro-

grammed to function in the address pipelining (memory

interleaving) mode. The DP8420/21/22 only allows

RFRQ to be output during the address pipelining mode.

8. Parameter Changes due to Loading

All A.C. parameters are specified with the equivalent load

capacitances, including traces, of 64 DRAMs organized

as 4 banks of 18 DRAMs each. Maximums are based on

worst-case conditions. If an output load changes then the

A.C. timing parameters associated with that particular

output must be changed. For example, if we changed our

output load to

4. Clearing the Refresh Request Clock Counter

The DP8420A/21A/22A allows the internal refresh re-

quest clock counter to be cleared by negating DISRFSH

and asserting RFSH for at least 500 ns. The

DP8420/21/22 clears the internal refresh request clock

counter if DISRFSH remains low for at least 500 ns. Once

the internal refresh request clock counter is cleared the

user is guaranteed that an internally generated RFRQ will

not be generated for at least 13 ms–15 ms (depending

e

C

250 pF loads on RAS0–3 and CAS0–3

760 pF loads on Q0–9 and WE

we would have to modify some parameters (not all calcu-

lated here)

$308a clock to CAS asserted

e

0 ns)

e

(t

15 ns, t

RAH

ASC

A ratio can be used to figure out the timing change per

change in capacitance for a particular parameter by using

the specifications and capacitances from heavy and light

load timing.

upon how programming bits C0, 1, 2,

grammed).

3 were pro-

15.0 DP8420A/21A/22A User Hints

1. All inputs to the DP8420A/21A/22A should be tied high,

low or the output of some other device.

b

$308a w/Heavy Load $308a w/Light Load

e

Ratio

b

(CAS) C (CAS)

L

C

H

b

79 ns

72 ns

50 pF

7 ns

Note: One signal is active high. COLINC (EXTNDRF) should be tied low

to disable.

e

b

125 pF

75 pF

2. Each ground on the DP8420A/21A/22A must be decou-

pled to the closest on-chip supply (V ) with 0.1 mF ce-

e

c

(capacitance difference

$308a (actual)

CC

ramic capacitor. This is necessary because these

a

ratio)

$308a (specified)

7 ns

e

b

a

79 ns

grounds

are

kept

separate

inside

the

(250 pF

125 pF)

79 ns

75 pF

DP8420A/21A/22A. The decoupling capacitors should

be placed as close as possible with short leads to the

ground and supply pins of the DP8420A/21A/22A.

e

a

11.7 ns

@

90.7 ns 250 pF load

9. It is required that the user perform a hardware reset of

the DP8420A/21A/22A before programming and using

the chip. A hardware reset consists of asserting both ML

and DISRFSH for a minimum of 16 positive edges of CLK,

see Section 3.1.

3. The output called ‘‘CAP’’ should have a 0.1 mF capacitor

to ground.

4. The DP8420A/21A/22A has 20X series damping resis-

tors built into the output drivers of RAS, CAS, address

and WE/RFRQ. Space should be provided for external

damping resistors on the printed circuit board (or wire-

57

Ý

Lit. 103064

Physical Dimensions inches (millimeters)

Plastic Chip Carrier (V)

Order Number DP8420AV-20, DP8420AV-25, DP8421AV-20 or DP8421AV-25

NS Package Number V68A

Plastic Chip Carrier (V)

Order Number DP8422AV-20 or DP8422AV-25

NS Package Number V84A

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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT

DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL

SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant

into the body, or (b) support or sustain life, and whose

failure to perform, when properly used in accordance

with instructions for use provided in the labeling, can

be reasonably expected to result in a significant injury

to the user.

2. A critical component is any component of a life

support device or system whose failure to perform can

be reasonably expected to cause the failure of the life

support device or system, or to affect its safety or

effectiveness.

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Corporation

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Hong Kong Ltd.

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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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型号：	DP8421AVX-20
厂家：	TEXAS INSTRUMENTS
描述：	DRAM CONTROLLER, PQCC68, PLASTIC, LCC-68 动态存储器外围集成电路
文件：	总60页 (文件大小：1073K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

DP8421AVX-20 [TI]

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