FX929BD2_技术文档

CML Semiconductor Products

4-Level FSK Modem Data Pump FX929B

Advance Information

D/929B/1 May 1997

Features

Applications

4800 to 19200 b/s Operation

RCR STD-47 and RD-LAP* Systems

Two-Way Paging Equipment

Mobile Data Systems

·

Full Packet Data Framing

4-Level FSK Data Modulation

Low Power, 2.5mA at 3.3V

Flexible Operating Modes

Powersave Option

Wireless Telemetry

DataTAC^ÒTerminals

Portable Wireless Data Equipment

*Radio Data-Link Access Procedure (RD-LAP) is a data communications air interface protocol developed by Motorola Inc.

1.1

Brief Description

The FX929B is a CMOS integrated circuit that contains all of the baseband signal processing and Medium

Access Control (MAC) protocol functions required for a high performance 4-level FSK Wireless Packet Data

Modem. It interfaces with the modem host processor and the radio modulation/demodulation circuits to deliver

reliable two-way transfer of the application data over the wireless link. The FX929B is backwards compatible

with the FX929A but offers better performance during radio link fading and selectable Tx symbol shapes.

The FX929B assembles application data received from the processor, adds forward error correction (FEC) and

error detection (CRC) information and interleaves the result for burst-error protection. After adding symbol and

frame synchronisation codewords, it converts the packet into a filtered 4-level analogue baseband signal for

modulating the radio transmitter.

In receive mode, the FX929B performs the reverse function using the analogue baseband signals from the

receiver discriminator. After error correction and removal of the packet overhead, the recovered application

data is supplied to the processor. Any residual uncorrected errors in the data will be flagged. A readout of the

SNR value during receipt of a packet is also provided.

The FX929B uses data block sizes and FEC/CRC algorithms compatible with the RD-LAP and RCR STD-47

over-air standards. The device is programmable to operate at most standard bit-rates from a wide choice of

Xtal/clock frequencies.

P4

D2

D5

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4-Level FSK Modem Data Pump

FX929B

CONTENTS

Section

Page

1.1 Brief Description.........................................................................................1

1.2 Block Diagram ............................................................................................3

1.3 Signal List...................................................................................................4

1.4 External Components.................................................................................6

1.5 General Description ...................................................................................7

1.5.1 Description of Blocks .................................................................7

1.5.2 Modem - µC Interaction ............................................................10

1.5.3 Binary to Symbol Translation...................................................11

1.5.4 Frame Structure ........................................................................12

1.5.5 The Programmer's View............................................................13

1.5.5.1 Data Block Buffer .....................................................................13

1.5.5.2 Command Register ..................................................................14

1.5.5.3 Control Register .......................................................................22

1.5.5.4 Mode Register..........................................................................24

1.5.5.5 Status Register.........................................................................25

1.5.5.6 Data Quality Register ...............................................................27

1.5.6 CRC, FEC, and Interleaving......................................................28

1.5.7 Transmitted Symbol Shape ......................................................29

1.6 Application Notes.....................................................................................31

1.6.1 Transmit Frame Examples........................................................31

1.6.2 Receive Frame Examples..........................................................34

1.6.3 Clock Extraction & Level Measurement Systems....................37

1.6.4 AC Coupling..............................................................................38

1.6.5 Radio Performance ...................................................................40

1.6.6 Received Signal Quality Monitor..............................................41

1.7 Performance Specification.......................................................................42

1.7.1 Electrical Performance..............................................................42

1.7.2 Packaging..................................................................................46

Note: As this product is still in development, it is likely that a number of changes and additions will

be made to this specification. Items marked TBD or left blank will be included in later issues.

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1.2

Block Diagram

Figure 1 Block Diagram

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1.3

Signal List

Package

P4/D2/D5

Signal

Description

Pin No.

Name

Type

1

IRQN

O/P

A 'wire-ORable' output for connection to the host

mC's Interrupt Request input. This output has a

low impedance pull down to V_SSwhen active

and is high impedance when inactive.

2

3

4

5

6

7

8

9

D7

D6

D5

D4

D3

D2

D1

D0

BI

)

8-bit bidirectional 3-state mC interface data

lines.

10

RDN

I/P

Read. An active low logic level input used to

control the reading of data from the modem into

the host mC.

11

WRN

I/P

Write. An active low logic level input used to

control the writing of data into the modem from

the host mC.

12

13

V

Power

I/P

The negative supply rail (ground).

ss

CSN

Chip Select. An active low logic level input to

the modem, used to enable a data read or write

operation.

14

15

A0

A1

I/P

)

Two logic level modem register select

inputs.

16

XTALN

O/P

I/P

The output of the on-chip oscillator.

17

XTAL/CLOCK

The input to the on-chip oscillator, for external

Xtal circuit or clock.

18

19

DOC 2

DOC 1

O/P

)

Connections to the Rx level measurement

circuitry. A capacitor should be connected

from each pin to V_SS.

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FX929B

Package

P4/D2/D5

Signal

Description

Pin No.

20

Name

TXOP

V_BIAS

Type

O/P

The Tx signal output from the modem.

A bias line for the internal circuitry, held at

21

O/P

½ V_DD. This pin must be decoupled to V_SSby a

capacitor mounted close to the device pins.

22

23

RXIN

I/P

The input to the Rx input amplifier.

RXFB

O/P

The output of the Rx input amplifier and the

input to the Rx RRC filter.

24

V_DD

Power

The positive supply rail. Levels and voltages are

dependent upon this supply. This pin should be

decoupled to V_SSby a capacitor.

Notes: I/P

=

Input

O/P = Output

BI Bidirectional

=

Internal protection diodes are connected from each signal pin to V_DDand V_SS

.

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1.4

External Components

Figure 2 Recommended External Components

R1

R2

R3

R4

X1

See Section 1.5.1

C1

C2

C3

C4

C5

C6

C7

C8

0.1 µF ± 20%

± 20%, see Note 1

± 5%, see Note 3

100k ohm ± 5%

1M ohm ± 20%

100k ohm ± 5%

± 20%, see Note 2

± 5%, see Note 3

See Section 1.5.5.3

Note 1: The values used for C3 and C4 should be suitable for the frequency of the crystal X1. As a

guide, values (including stray capacitances) of 33pF at 1MHz falling to 18pF at 10MHz will generally

prove suitable. The 'Phase-Locked Loop Modes' part of section 1.5.5.3 discusses crystal frequency

tolerances.

Note 2: C6 and C7 values (in nano Farads) should be equal to 50000 ¸ symbol rate, e.g.

Symbol Rate

C6 and C7 (nF)

2400 symbols/second

4800 symbols/second

9600 symbols/second

22.0

10.0

4.7

Note 3: C5 and C8 values (in pico Farads) should be equal to 750000 ¸ symbol rate, e.g.

Symbol Rate

C5 and C8 (pF)

2400 symbols/second

4800 symbols/second

9600 symbols/second

330

150

82

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1.5

General Description

1.5.1

Description of Blocks

Data Bus Buffers

Eight bidirectional 3-state logic level buffers between the modem's internal registers and the host µC's data

bus lines.

Address and R/W Decode

This block controls the transfer of data bytes between the µC and the modem's internal registers, according to

the state of the Write and Read Enable inputs (WRN and RDN), the Chip Select input (CSN) and the Register

Address inputs A0 and A1.

The Data Bus Buffers, Address and R/W Decode blocks provide a byte-wide parallel µC interface, which can

be memory-mapped, as shown in Figure 3.

Figure 3 Typical Modem µC Connections

Status and Data Quality Registers

Two 8-bit registers which the µC can read to determine the status of the modem and the received data quality.

Command, Mode and Control Registers

The values written by the µC to these 8-bit registers control the operation of the modem.

Data Buffer

A 12-byte buffer used to hold receive or transmit data to or from the µC.

CRC Generator/Checker

A circuit which generates (in transmit mode) or checks (in receive mode) the Cyclic Redundancy Checksum

bits, which may be included in transmitted data blocks so that the receive modem can detect transmission

errors.

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FEC Generator/Checker

In transmit mode, this circuit adds Forward Error Correction bits to the transmitted data, then converts the

resulting binary data to 4-level symbols. In receive mode, it translates received 4-level symbols to binary data,

using the FEC information to correct a large proportion of transmission errors.

Interleave/De-interleave Buffer

This circuit interleaves data symbols within a block before transmission and de-interleaves the received data

so that the FEC system is best able to handle short noise bursts or fades.

Frame Sync Detect

This circuit, which is only active in receive mode, is used to look for the 24-symbol Frame Synchronisation

pattern which is transmitted to mark the start of every frame.

Rx I/P Amp

This amplifier allows the received signal input to the modem to be set to the optimum level by suitable

selection of the external components R1 and R2. The value of R1 should be calculated to give 0.2 x V_DDpk-

pk at the RXFB pin for a received '...+3 +3 -3 -3 ...' sequence.

A capacitor may be fitted in series with R1 if ac coupling of the received signal is desired (see Section 1.6.4),

otherwise the dc level of the received signal should be adjusted so that the signal at the modem's RXFB pin is

centred around V_BIAS(½ V_DD).

RRC Low Pass Filter

This filter, which is used in both transmit and receive modes, is a linear-phase lowpass filter with a 'Root

Raised Cosine' frequency response defined by:

H(f) = 1

= square root of {0.5 [1 - sin(p T (f - 0.5/T)/b)]} for

= 0 for

for

0

<= f < (1-b)/(2T)

(1-b)/(2T) <= f <= (1+b)/(2T)

(1+b)/(2T) <

f

where b = 0.2, T = 1/symbol rate

In transmit mode, the 4-level symbols are passed through this filter to eliminate the high frequency

components which would otherwise cause interference into adjacent radio channels.

Figure 4 Generation of RRC Filtered 4-Level Tx Baseband Signal

The input applied to the RRC Tx filter may be impulses or full-width symbols depending on the setting of the

Command Register TXIMP bit, see section 1.5.7.

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In receive mode, the filter is used to reject HF noise and to equalise the received signal to a form suitable for

extracting the 4-level symbols, the equalisation characteristics depending on the setting of the Command

Register TXIMP bit.

0

-5

-10

dB -15

-20

-25

-30

0

0.2

0.4

0.6

0.8

1

Frequency / Symbol rate

Figure 5 RRC Filter Frequency Response (including the external RC filter R4/C5)

Tx Output Buffer

This is a unity gain amplifier used in transmit mode to buffer the output of the Tx low pass filter. In receive

mode, the input of this buffer is connected to V_BIASunless the RXEYE bit of the Control Register is '1', when it

is connected to the received signal. When changing from Rx to Tx mode the input to this buffer will be

connected to V_BIASfor 8 symbol times while the RRC filter settles.

Note: The RC low pass filter formed by the external components R4 and C5 between the TXOP pin and the

input to the radio's frequency modulator forms an important part of the transmit signal filtering. These

components may form part of any dc level-shifting and gain adjustment circuitry. The value used for C5 should

take into account stray circuit capacitances, and its ground connection should be positioned to give maximum

attenuation of high frequency noise into the modulator.

The signal at the TXOP pin is centred around V_BIASand is approx 0.2 x V_DDpk-pk for a continuous '+3 +3 -3

-3 ...' pattern with TXIMP = 0.

A capacitor may be fitted in series with the input to the frequency modulator if ac coupling is desired, see

Section 1.6.4.

Figure 6 Transmitted Signal Eye Diagram (TXIMP = 0, see section 1.5.7)

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Rx Level/Clock Extraction

These circuits, which operate only in receive mode, derive a symbol rate clock from the received signal and

measure the received signal amplitude and dc offset. This information is then used to extract the received 4-

level symbols and also to provide an input to the received Data Quality measuring circuit. The external

capacitors C6 and C7 form part of the received signal level measuring circuit. The capacitors C6 and C7 are

driven from a very high impedance source so any measurement of the voltages on the DOC pins must be

made via high input impedance (MOS input) voltage followers to avoid disturbance of the level measurement

circuits.

Further details of the level and clock extraction functions are given in section 1.6.3.

Clock Oscillator and Dividers

These circuits derive the transmit symbol rate (and the nominal receive symbol rate) by frequency division of a

reference frequency which may be generated by the on-chip Xtal oscillator or applied from an external source.

Note: If the on-chip xtal oscillator is to be used, then the external components X1, C3, C4 and R3 are

required. If an external clock source is to be used, then it should be connected to the XTAL/CLOCK input pin,

the XTALN pin should be left unconnected, and X1, C3, C4 and R3 not fitted.

1.5.2 Modem - µC Interaction

In general, data is transmitted over-air in the form of messages, or 'Frames', consisting of a 'Frame Preamble'

followed by one or more formatted data blocks. The Frame Preamble includes a Frame Synchronisation

pattern designed to allow the receiving modem to identify the start of a frame. The following data blocks are

constructed from the 'raw' data using a combination of CRC (cyclic redundancy checksum) generation,

Forward Error Correction coding and Interleaving. Details of the message formats handled by the modem are

given in Section 1.5.3 and Figures 7 and 7a.

To reduce the processing load on the associated mC, the FX929B modem has been designed to perform as

much as possible of the computationally intensive work involved in Frame formatting and de-formatting and -

when in receive mode - in searching for and synchronising onto the Frame Preamble. In normal operation the

modem will only require servicing by the µC once per received or transmitted block.

Thus, to transmit a block, the controlling µC has only to load the - unformatted - 'raw' binary data into the

modem's Data Block Buffer then instruct the modem to format and transmit that data. The modem will then

calculate and add the CRC bits as required, encode the result as 4-level symbols (with Forward Error

Correction coding) and interleave the symbols before transmission.

In receive mode, the modem can be instructed to assemble a block's worth of received symbols, de-interleave

the symbols, translate them to binary - using the FEC coding to correct as many errors as possible - and

check the resulting CRC before placing the received binary data into the Data Block Buffer for the µC to read.

The modem can also transmit and receive un-formatted data using the T4S, T24S and R4S tasks described in

sections 1.5.3 and 1.5.5.2. These are normally used for the transmission of Symbol and Frame

Synchronisation sequences. They may also be used for the transmission and reception of special test patterns

or even for special data formats - although in this case care should be taken to ensure that the transmitted

signal contains enough level and timing information for the receiving modem's level and clock extraction

circuits to function correctly (see section 1.6.3).

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1.5.3

Binary to Symbol Translation

Although the over-air signal, and hence the signals at the modem TXOP and RXIN pins, consists of 4-level

symbols, the raw data passing between the modem and the µC is in binary form. Translation between binary

data and the 4-level symbols is done in one of two ways, depending on the task being performed.

Direct: the simplest form, which converts between 2 binary bits and a single symbol, such as the 'S' Channel

Status symbol.

symbol

ms bit

ls bit

+3

+1

-1

1

0

1

0

1

-3

This is expanded so that an 8-bit byte translates to four symbols for the T4S, T24S and R4S tasks described

in Section 1.5.5.2.

msb

7

lsb

0

Bits:

6

5

4

3

2

1

Symbols:

a

b

c

d

sent first

sent last

With FEC: This is more complicated, but essentially translates groups of 3 binary bits to pairs of 4-level

symbols using a Forward Error Correcting coding scheme for the block oriented tasks THB, TIB, TLB, TSID,

RHB, RILB and RSID described in Section 1.5.5.2.

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1.5.4

Frame Structure

The FX929B Frame Structure as used in a RD-LAP system is illustrated in Figure 7, and consists of a Frame

Preamble (comprising a 24-symbol Frame Synchronisation pattern and Station ID block) followed by a 'Header

Block', one or more 'Intermediate Blocks and a 'Last Block'. Channel Status (S) symbols are included at

regular intervals. The first Frame of any transmission is preceded by a Symbol Synchronisation pattern.

Header Block

Intermediate Blocks

Last Block

Station ID

msb

7

lsb

0

6

5

4

3

2

1

7

6

5

4

3

2

1

0

7

6

5

4

3

2

1

0

7

6

5

4

3

2

1

0

Byte 0

Byte 1

System ID

Domain ID

Byte 0

Byte 1

Byte 2

Byte 3

Byte 4

Byte 5

Byte 6

Byte 7

Byte 8

Data bytes

(0 - 8)

Byte 2

Byte 3

Base ID

CRC0

Address

&

Data Bytes

(12)

Control

Pad bytes

(0 - 8)

(10 bytes)

CRC2

(4 bytes)

Byte 9

Byte 10

CRC1

(2 bytes)

Byte 11

2

7

0

2

7

0

7

0

7

0

7

0

2

7

0

7

0

Byte 0

Byte 1

Byte 2

Byte 3

Byte 0

Byte 1

Byte 11

'000'

10

0

1

9

8

tri-bits

0

1

3

4

5

29

30

31

32

FEC TRELLIS CODING / DECODING

( ERROR CORRECTION )

FEC TRELLIS CODING / DECODING

( ERROR CORRECTION )

4 -level

65

2

64

0

1

21

20

sy m bols

INTERLEAVING / DE-INTERLEAVING

Block:

S

22 symbols

S

22 symbols

Over-air

signal

'HEADER'

BLOCK

SYMBOL

SYNC

FRAME

SYNC

STATION

ID

FRAME

SYNC

'LAST'

BLOCK

S

INTERMEDIATE BLOCKS

(symbols)

1

24

1

22

69

PACKET (1 TO 44 BLOCKS)

FRAME

PREAMBLE

NEXT FRAME

(OPTIONAL)

'S' : Channel Status Symbol : +3 = Busy +1 = Unknown -1 = Unknown -3 = Idle

Frame Sync:

-1

+1

-1

+1

-1

+3

-3 +3

-3

-1 +1

-3 +3

+3

-1

-3

+1

-3

-3 +1

+3

-3

-1

-3

-3 +1

-3 +3

+3

Symbol Sync:

+3 +3

-3

-3 +3

+3

-3

-3 +3

+3

-3

-3 +3

+3

-3

+3

sent first

last

Figure 7 Over Air Signal Format

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The 'Header' block is self-contained in that it includes its own checksum (CRC1), and would normally carry

information such as the address of the calling and called parties, the number of following blocks in the frame (if

any) and miscellaneous control information.

The 'Intermediate' block(s) contain only data, the checksum at the end of the 'Last' block (CRC2) also checks

the data in any preceding 'Intermediate' blocks.

Proprietary systems which do not use the RD-LAP format may use the block structures provided by the

FX929B to build alternative frame formats more suited to the particular application. Some examples are

illustrated in Figure 7a below.

Figure 7a Some Alternative Frame Structures

The FX929B performs all of the block formatting and de-formatting, the binary data transferred between the

modem and its mC being that enclosed by the thick dashed rectangles near the top of Figure 7.

1.5.5 The Programmer's View

The modem appears to the programmer as 4 write only 8-bit registers shadowed by 3 read only registers,

individual registers being selected by the A0 and A1 chip inputs:

A1

0

A0

0

Write to Modem

Data Buffer

Read from Modem

Data Buffer

0

1

0

1

Command Register

Control Register

Mode Register

Status Register

Data Quality Register

not used

Note that there is a minimum allowable time between accesses of the modem's registers, see Section 1.7.1 for

details.

1.5.5.1 Data Block Buffer

This is a 12-byte read/write buffer which is used to transfer data (as opposed to command, status, mode, data

quality or control information) between the modem and the host µC.

It appears to the µC as a single 8-bit register; the modem ensuring that sequential µC reads or writes to the

buffer are routed to the correct locations within the buffer.

The µC should only access this buffer when the Status Register BFREE (Buffer Free) bit is '1'.

The buffer should only be written to while in Tx mode and read from while in Rx mode. Note that in receive

mode the modem will function correctly even if the received data is not read from the Data Buffer by the mC.

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1.5.5.2 Command Register

Writing to this register tells the modem to perform a specific action or actions, depending on the setting of the

TASK, AQLEV and AQSC bits.

When it has no action to perform, the modem will be in an 'idle' state. If the modem is in transmit mode the

input to the Tx RRC filter will be connected to V_BIAS. In receive mode the modem will continue to measure the

received data quality and extract symbols from the received signal, supplying them to the de-interleave buffer,

but will otherwise ignore the received data.

Command Register B7: AQSC - Acquire Symbol Clock

This bit has no effect in transmit mode.

In receive mode, whenever a byte with the AQSC bit set to '1' is written to the Command Register, and TASK

is not set to RESET, it initiates an automatic sequence designed to achieve symbol timing synchronisation with

the received signal as quickly as possible. This involves setting the Phase Locked Loop of the received bit

timing extraction circuits to its widest bandwidth, then gradually reducing the bandwidth as timing

synchronisation is achieved, until it reaches the 'normal' value set by the PLLBW bits of the Control Register.

Setting this bit to '0' (or changing it from '1' to '0') has no effect, however note that the acquisition sequence will

be re-started every time that a byte written to the Command Register has AQSC = '1'.

The use of the symbol clock acquisition sequence is described in section 1.6.3.

Command Register B6: AQLEV - Acquire Receive Signal Levels

This bit has no effect in transmit mode.

In receive mode, whenever a byte with the AQLEV bit set to '1' is written to the Command Register and TASK

is not set to RESET, it initiates an automatic sequence designed to measure the amplitude and dc offset of the

received signal as rapidly as possible. This sequence involves setting the measurement circuits to respond

quickly at first, then gradually increasing their response time, hence improving the measurement accuracy,

until the 'normal' value set by the LEVRES bits of the Control Register is reached.

Setting this bit to '0' (or changing it from '1' to '0') has no effect, however note that the acquisition sequence will

be re-started every time that a byte written to the Command Register has AQLEV = '1'.

The use of the level measurement acquisition sequence (AQLEV) is described in section 1.6.3.

Command Register B5: CRC

This bit allows the user to select between two different forms of the CRC0, CRC1 and CRC2 checksums.

When this bit is set to '1' the CRC generators are initialised to 'all zeros', as required by RD-LAP systems.

When this bit is set to '0' the CRC generators are initialised to 'all ones' as required by CCITT X25 based

systems. It should always be set to '1' for RD-LAP compatibility, other systems may set this bit as required.

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Command Register B4: TXIMP

This bit allows the user to choose between two transmit symbol shapes as described in section 1.5.7. Note

that this bit must be set correctly every time the Command Register is written to.

Command Register B3

This bit should always be set to '0'.

Command Register B2, B1, B0: TASK

Operations such as transmitting or receiving a data block are treated by the modem as 'tasks' and are initiated

when the µC writes a byte to the Command Register with the TASK bits set to anything other than the 'NULL'

code.

The µC should not write a task (other than NULL or RESET) to the Command Register or write to or read from

the Data Buffer when the BFREE (Buffer Free) bit of the Status Register is '0'.

Different tasks apply in receive and transmit modes.

When the modem is in transmit mode, all tasks other than NULL or RESET instruct the modem to transmit

data from the Data Buffer, formatting it as required. The µC should therefore wait until the BFREE (Buffer

Free) bit of the Status Register is '1', before writing the data to the Data Block Buffer, then it should write the

desired task to the Command Register. If more than 1 byte needs to be written to the Data Block Buffer, byte

number 0 of the block should be written first.

Once the byte containing the desired task has been written to the Command Register, the modem will:

Set the BFREE (Buffer Free) bit of the Status Register to '0'.

Take the data from the Data Block Buffer as quickly as it can - transferring it to the Interleave Buffer

for eventual transmission. This operation will start immediately if the modem is 'idle' (i.e. not

transmitting data from a previous task), otherwise it will be delayed until there is sufficient room in the

Interleave Buffer.

Once all of the data has been transferred from the Data Block Buffer the modem will set the BFREE

and IRQ bits of the Status Register to '1', (causing the chip IRQN output to go low if the IRQNEN bit of

the Mode Register has been set to '1') to tell the µC that it may write new data and the next task to the

modem.

This lets the µC write a task and the associated data to the modem while the modem is still transmitting the

data from the previous task.

Task 2

Task 1

Data from µC to Block Buffer

Task from µC to Command Register

BFREE bit of Status Register

IRQ bit of Status Register

IRQN o/p (IRQNEN = '1')

from task 2

TXOP signal

from task 1

Figure 8 Transmit Task Overlapping

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4-Level FSK Modem Data Pump

FX929B

When the modem is in receive mode, the µC should wait until the BFREE bit of the Status Register is '1', then

write the desired task to the Command Register.

Once the byte containing the desired task has been written to the Command Register, the modem will:

Set the BFREE bit of the Status Register to '0'.

Wait until enough received symbols are in the De-interleave Buffer.

Decode them as needed, and transfer the resulting binary data to the Data Block Buffer

Then the modem will set the BFREE and IRQ bits of the Status Register to '1', (causing the IRQN

output to go low if the IRQNEN bit of the Mode Register has been set to '1') to tell the µC that it may

read from the Data Block Buffer and write the next task to the modem. If more than 1 byte is

contained in the buffer, byte number 0 of the data will be read out first.

In this way the µC can read data and write a new task to the modem while the received symbols needed for

this new task are being received and stored in the De-interleave Buffer.

RXIN signal

for task 1

for task 2

IRQN o/p (IRQNEN = '1')

IRQ bit of Status Register

BFREE bit of Status Register

Task 1

Task from µC to Command Register

Data from Block Buffer to µC

Task 2

Task 1 data

Figure 9 Receive Task Overlapping

Detailed timings for the various tasks are given in Figures 10 and 11.

FX929B Modem Tasks:

B2 B1 B0

Receive Mode

Transmit Mode

0

1

0

1

0

1

NULL

SFP

RHB

RILB

NULL

T24S

THB

TIB

Search for Frame Preamble

Read Header Block

Read Intermediate or Last

Block

Transmit 24 symbols

Transmit Header Block

Transmit Intermediate Block

1

0

1

0

1

0

1

SFS

R4S

RSID

Search for Frame Sync

Read 4 symbols

Read Station ID

TLB

T4S

TSID

Transmit Last Block

Transmit 4 symbols

Transmit Station ID

RESET Cancel any current action

NULL: No effect

This task is provided so that a AQSC or AQLEV command can be initiated without loading a new task.

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4-Level FSK Modem Data Pump

FX929B

SFP: Search for Frame Preamble

This task causes the modem to search the received signal for a valid Frame Preamble, consisting of a 24-

symbol Frame Sync sequence followed by Station ID data which has a correct CRC0 checksum.

The task continues until a valid Frame Preamble has been found.

The search consists of four stages:

First of all the modem will attempt to match the incoming symbols against the Frame Synchronisation

pattern to within the tolerance defined by the FSTOL bits of the Control Register.

Once a match has been found, the modem will read in the following 'S' symbol, place it in the SVAL

bits of the Status Register then set the SRDY bit to '1'. (The IRQ bit of the Status Register will also be

set to '1' at this time if the SSIEN bit of the Mode Register is '1').

The modem will then read the next 22 symbols as station ID data. They will be decoded and the CRC0

checked. If this is incorrect, the modem will resume the search, looking for a fresh Frame Sync

pattern.

If the received CRC0 is correct, the following 'S' symbol will be read into the SVAL bits of the Status

Register and the SRDY, BFREE and IRQ bits set to '1', the CRCERR bit cleared to '0', and the three

decoded Station ID bytes placed into the Data Block Buffer.

On detecting that the BFREE bit of the Status Register has gone to '1', the µC should read the 3 Station ID

bytes from the Data Block Buffer then write the next task to the modem's Command Register.

RHB: Read Header Block

This task causes the modem to read the next 69 symbols as a 'Header' Block. It will strip out the 'S' symbols

then de-interleave and decode the remaining 66 symbols, placing the resulting 10 data bytes and the 2

received CRC1 bytes into the Data Block Buffer, and setting the BFREE and IRQ bits of the Status Register to

'1' when the task is complete to indicate that the µC may read the data from the Data Block Buffer and write

the next task to the modem's Command Register.

The CRCERR bit of the Status Register will be set to '1' or '0' depending on the validity of the received CRC1

checksum bytes.

As each of the 3 'S' symbols of a block is received, the SVAL bits of the Status Register will be updated and

the SRDY bit set to '1'. (If the SSIEN bit of the Mode Register is '1', then the Status Register IRQ bit will also

be set to '1'.) Note that when the third 'S' symbol is received, the SRDY bit will be set to '1' coincidentally with

the BFREE bit also being set to '1'.

RILB: Read 'Intermediate' or 'Last' Block

This task causes the modem to read the next 69 symbols as an 'Intermediate' or 'Last' block (the µC can tell

from the 'Header' block how many blocks are in the frame, and hence when to expect the 'Last' block).

In each case, it will strip out the 3 'S' symbols, de-interleave and decode the remaining 66 symbols and place

the resulting 12 bytes into the Data Block Buffer, setting the BFREE and IRQ bits of the Status Register to '1'

when the task is complete.

If an 'Intermediate' block is received then the µC should read out all 12 bytes from the Data Block Buffer and

ignore the CRCERR bit of the Status Register, for a 'Last' block the µC need only read the first 8 bytes from

the Data Block Buffer, and the CRCERR bit in the Status Register will reflect the validity of the received CRC2

checksum.

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

As each of the 3 'S' symbols of the block is received, the SVAL bits of the Status Register will be updated and

the SRDY bit set to '1'. (If the SSIEN bit of the Mode Register is '1', then the Status Register IRQ bit will also

be set to '1'.) Note that when the third 'S' symbol is received, the SRDY bit will be set to '1' coincidentally with

the BFREE bit also being set to '1'.

SFS: Search for Frame Sync

This task - which is intended for special test and channel monitoring purposes - performs the first two parts

only of a SFP task. It causes the modem to search the received signal for a 24-symbol sequence which

matches the required Frame Synchronisation pattern to within the tolerance defined by the FSTOL bits of the

Mode Register.

When a match is found the modem will read in the following 'S' symbol, then set the BFREE, IRQ and SRDY

bits of the Status Register to '1' and update the SVAL bits. The µC may then write the next task to the

Command Register.

R4S: Read 4 Symbols

This task causes the modem to read the next 4 symbols and translate them directly (without de-interleaving or

FEC) to an 8-bit byte which is placed into the Data Block Buffer. The BFREE and IRQ bits of the Status

Register will then be set to '1' to indicate that the µC may read the data byte from the Data Block Buffer and

write the next task to the Command Register.

This task is intended for special tests and channel monitoring - perhaps preceded by SFS task.

Note that although it is possible to construct message formats which do not rely on the block formatting of the

THB, TIB and TLB tasks by using T4S or T24S tasks to transmit and R4S to receive the user’s data, anyone

attempting this should be aware that the receive level and timing measurement circuits need to see a

reasonably ‘random’ distribution of all four possible symbols in the received signal to operate correctly, and

should therefore ‘scramble’ the binary data before transmission.

RSID: Read Station ID

This task causes the modem to read in and decode the following 23 symbols as Station ID data followed by an

'S' symbol. It is similar to the last two parts of a SFP task except that it will not re-start if the received CRC0 is

incorrect. It would normally follow a SFS task.

The 3 decoded bytes will be placed into the Data Block Buffer, and the CRCERR bit of the Status Register set

to '1' if the received CRC0 was incorrect, otherwise it will be cleared to '0'. The SVAL bits of the Status

Register will be updated and the BFREE, SRDY and IRQ bits set to '1' to indicate that the µC may read the 3

received bytes from the Data Block Buffer and write the next task to the modem's Command Register.

T24S: Transmit 24 Symbols

This task, which is intended to facilitate the transmission of Symbol and Frame Sync patterns as well as

special test sequences, takes 6 bytes of data from the Data Block Buffer and transmits them as 24 4-level

symbols without any CRC, FEC, interleaving or adding any 'S' symbols.

Byte 0 of the Data Block Buffer is sent first, byte 5 last.

Once the modem has read the data bytes from the Data Block Buffer, the BFREE and IRQ bits of the Status

Register will be set to '1', indicating to the µC that it may write the data and command byte for the next task to

the modem.

The tables below show what data has to be written to the Data Block Buffer to transmit the FX929B Symbol

and Frame Sync sequences:

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

'Symbol Sync'

Symbols

Values written to Data Block Buffer

Binary

Hex

+3

-3

+3

-3

Byte 0:

Byte 1:

Byte 2:

Byte 3:

Byte 4:

Byte 5 :

11110101

01011111

F5

5F

+3

'Frame Sync'

Symbols

Values written to Data Block Buffer

Binary

Hex

22

-1

-3

+3

-3

-1

+1

+3

-1

+3

-3

-1

-3

+1

-1

+1

+3

-3

+1

+3

Byte 0:

Byte 1:

Byte 2:

Byte 3:

Byte 4:

Byte 5:

00100010

00110111

01001001

11110010

01011011

00011011

37

49

F2

5B

1B

-3

THB: Transmit Header Block

This task takes 10 bytes of data (Address and Control) from the Data Block Buffer, calculates and appends

the 2-byte CRC1 checksum, translates the result to 4-level symbols (with FEC), interleaves the symbols and

transmits the result as a formatted 'Header' Block , inserting 'S' symbols at 22-symbol intervals.

Once the modem has read the data bytes from the Data Block Buffer, the BFREE and IRQ bits of the Status

Register will be set to '1'.

TIB: Transmit Intermediate Block

This task takes 12 bytes of data from the Data Block Buffer, updates the 4-byte CRC2 checksum for inclusion

in the 'Last' block, translates the 12 data bytes to 4-level symbols (with FEC), interleaves the symbols and

transmits the result as a formatted 'Intermediate' Block , inserting 'S' symbols at 22-symbol intervals.

Once the modem has read the data bytes from the Data Block Buffer, the BFREE and IRQ bits of the Status

Register will be set to '1'.

TLB: Transmit Last Block

This task takes 8 bytes of data from the Data Block Buffer, updates and appends the 4-byte CRC2 checksum,

translates the resulting 12 bytes to 4-level symbols (with FEC), interleaves the symbols and transmits the

result as a formatted 'Last' Block , inserting 'S' symbols at 22-symbol intervals.

Once the modem has read the data bytes from the Data Block Buffer, the BFREE and IRQ bits of the Status

Register will be set to '1'.

T4S: Transmit 4 Symbols

This task is similar to T24S but takes only one byte from the Data Block Buffer, transmitting it as four 4-level

symbols.

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

TSID: Transmit Station ID

This task takes 3 ID bytes from the Data Block Buffer, calculates and appends the 6-bit CRC0 checksum,

translates the result to 4-level symbols (with FEC) and transmits the resulting 22 symbols preceded and

followed by 'S' symbols.

Once the modem has read the data bytes from the Data Block Buffer, the BFREE and IRQ bits of the Status

Register will be set to '1'.

RESET: Stop any current action

This 'task' takes effect immediately, and terminates any current action (task, AQSC or AQLEV) the modem

may be performing and sets the BFREE bit of the Status Register to '1', without setting the IRQ bit. It should

be used when V

is applied, to set the modem into a known state.

DD

Note that due to delays in the RRC filter, it will take several symbol times for any change to appear at the

TXOP pin.

Task Timings

Data to Data Block Buffer

Task to Command Register

3

1

2

1

2

3

t4

t3

t4

t3

t4

IBEMPTY bit

BFREE bit

t2

t1

t3

Symbols to

RRC filter

from task #2

from task #3

from task #1

Modem Tx output

Figure 10 Transmit Task Timing Diagram

Task

Time

(symbol times)

t1

Modem in idle state. Time from writing first

task to application of first transmit bit to Tx

Any

1 to 2

RRC filter

t2

Time from application of first symbol of the

task to the Tx RRC filter until BFREE goes

to a logic '1' (high).

T24S

TSID

THB/TIB/TLB

T4S

5

6

16

0

t3

t4

Time to transmit all symbols of the task

T24S/TSID

THB/TIB/TLB

T4S

T24S

TSID

THB/TIB/TLB

T4S

24

69

4

18

17

52

3

Max time allowed from BFREE going to a

logic '1' (high) for next task (and data) to

be written to modem

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

Modem Rx input

for task #1

t3

for task #2

t3

for task #3

t3

Symbols to

De-interleave circuit

Data from Data Block Buffer

Task to Command Register

1

2

3

1

2

3

t7

t6

t7

BFREE bit

Figure 11 Receive Task Timing Diagram

Time

Task

(symbol times)

t3

t6

t7

Time to receive all symbols of task

SFS

SFP

RSID

RHB/RILB

R4S

SFS

SFP

RSID

RHB/RILB

R4S

25 (minimum)

48 (minimum)

23

69

4

21

15

51

3

Maximum time between first symbol of task

entering the de-interleave circuit and the

task being written to modem.

Maximum time from the last bit of the task

entering the de-interleave circuit to BFREE

going to a logic '1' (high)

Any

1

RRC Filter Delay

The previous task timing figures are based on the signal at the input to the RRC filter (in transmit mode) or the

input to the de-interleave buffer (in receive mode). There is an additional delay of about 8 symbol times

through to the RRC filter in both transmit and receive modes, as illustrated below:

Tx Symbol to RRC Filter

Tx Symbol at Txop pin / Rx Symbol from FM discriminator

Rx Symbol to De-interleave Buffer

Symbol-times

Figure 12 RRC Low Pass Filter Delay

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

1.5.5.3 Control Register

This 8-bit write-only register controls the modem's symbol rate, the response times of the receive clock

extraction and signal level measurement circuits and the Frame Sync pattern recognition tolerance.

Control Register B7, B6: CKDIV - Clock Division Ratio

These bits control a frequency divider driven from the clock signal present at the XTALN pin, and hence

determine the nominal symbol rate. The table below shows how symbol rates of 2400/4800/9600 symbols/sec

may be obtained from common Xtal frequencies:

Xtal Frequency (MHz)

2.4576

4.9152

9.8304

Division Ratio:

B6 Xtal Frequency/Symbol Rate

Symbol Rate (symbols/sec)

B7

0

1

0

1

0

1

512

4800

2400

9600

4800

2400

1024

2048

4096

9600

4800

2400

Note: Device operation is not guaranteed below 2400 or above 9600 symbols/sec.

Control Register B5, B4: FSTOL - Frame Sync Tolerance

These two bits have no effect in transmit mode. In receive mode, they define the maximum number of

mismatches which will be allowed during a search for the Frame Sync pattern:

B5 B4

Mismatches allowed

0

1

0

1

0

1

0

2

4

6

Note: A single 'mismatch' is defined as the difference between two adjacent symbol levels, thus if the symbol

'+1' were expected, then received symbol values of '+3' and '-1' would count as 1 mismatch, a received symbol

value of '-3' would count as 2 mismatches. A setting of '4 mismatches' is recommended for normal use.

Control Register B3, B2: LEVRES - Level Measurement Modes

These two bits have no effect in transmit mode. In receive mode they set the 'normal' operating mode of the

received signal amplitude and dc offset measuring circuits (the automatic sequencing of an AQLEV command

may temporarily override the 'normal' setting).

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4-Level FSK Modem Data Pump

FX929B

Mode

B3

0

1

B2

0

1

0

1

Hold

Level Track

Lossy Peak Detect

Slow Peak Detect

In normal use the LEVRES bits should be set to '0 1' (Level Track), the other modes are intended for special

purposes, for device testing, or are invoked automatically during an AQLEV sequence.

In ‘Slow Peak Detect’ modes the positive and negative excursions of the received signal (after filtering) are

measured by peak rectifiers driving the DOC1 and DOC2 capacitors to establish the amplitude of the signal

and any dc offset wrt VBIAS. This mode provides good overall performance, particularly when acquiring level

information at the start of a received message, but does not work well with certain long sequences of repeated

data byte values. It is also susceptible to large amplitude noise spikes such as can be generated during deep

fades.

The ‘Lossy Peak Detect’ mode is similar to ‘Slow Peak Detect’ but the capacitor discharge time constant is

much shorter, so this mode is not suitable for normal data reception and is only used within part of the

automatic AQLEV acquisition sequence.

In ‘Level Track’ mode the DOC capacitor voltages are slowly adjusted by the FX929B in such a way as to

minimise the average errors seen in the received signal. This mode provides the best overall performance,

being much more immune to large amplitude noise spikes than ‘Slow Peak Detect’ and being much less

sensitive to long sequences of repeated data byte values. It does, however, depend on the measured levels

and timing being approximately correct. If either of these is significantly wrong then the correction algorithm

used by the ‘Level Track’ mode can actually drive the voltages on the DOC capacitors away from their

optimum levels. For this reason the automatic AQLEV acquisition sequence (see 1.6.3) forces the level

measuring circuits into ‘Slow Peak Detect’ mode until a Frame Sync pattern has been found.

The DOC capacitors are isolated from the charging and discharging circuits in ‘Hold mode, allowing the

voltages to float.

Control Register B1, B0: PLLBW - Phase-Locked Loop Modes

These two bits have no effect in transmit mode. In receive mode, they set the 'normal' bandwidth of the Rx

clock extraction Phase Locked Loop circuit. This setting will be temporarily overridden by the automatic

sequencing of an AQSC command.

B1 B0 PLL Mode

0

1

0

1

0

1

Hold

Narrow Bandwidth

Medium Bandwidth

Wide Bandwidth

The normal setting for the PLLBW bits should be 'Medium Bandwidth' when the received symbol rate and the

frequency of the receiving modem's Xtal are both within ±100ppm of nominal, except at the start of a symbol

clock acquisition sequence (AQSC) when 'Wide Bandwidth' should be selected as described in section 1.6.3.

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

If the received symbol rate and Xtal frequency are both within ±20ppm of nominal then selection of the 'Narrow

Bandwidth' setting will give better performance, especially through fades or noise bursts which might otherwise

pull the PLL away from its optimum timing, but in this case it is recommended that the PLLBW bits are only set

to 'Narrow Bandwidth' after the modem has been running in 'Medium Bandwidth' mode for about 200 symbol

times.

The 'Hold' setting disables the feedback loop of the PLL, which continues to run at a rate determined only by

the actual Xtal frequency and the setting of the Control Register CKDIV bits.

1.5.5.4 Mode Register

The contents of this 8-bit write only register control the basic operating modes of the modem:

Mode Register B7: IRQNEN - IRQN Output Enable

When this bit is set to '1', the IRQN chip output pin is pulled low (to V ) whenever the IRQ bit of the Status

ss

Register is a '1'.

Mode Register B6: INVSYM - Invert Symbols

This bit controls the polarity of the transmitted and received symbol voltages.

B6

0

Symbol

'+3'

Signal at TXOP

Above V_BIAS

Below V_BIAS

Signal at RXFB

Below V_BIAS

Above V_BIAS

'-3'

1

'+3'

'-3'

Below V_BIAS

Above V_BIAS

Below V_BIAS

Mode Register B5: TXRXN - Tx/Rx Mode

Setting this bit to '1' puts the modem into Transmit mode, clearing it to '0' puts the modem into Receive mode.

Note that changing between receive and transmit modes will cancel any current task.

Mode Register B4: RXEYE - Show Rx Eye

This bit should normally be set to '0'.

Setting it to '1' when the modem is in receive mode configures the modem into a special test mode, in which

the input of the Tx o/p buffer is connected to the Rx Symbol/Clock extraction circuit at a point which carries the

equalised receive signal. This may be monitored with an oscilloscope (at the TXOP pin itself), to assess the

quality of the complete radio channel including the Tx and Rx modem filters, the Tx modulator and the Rx IF

filters and FM demodulator.

The resulting eye diagram (for reasonably random data) should ideally be as shown in Figure 13, with 4 'crisp'

and equally spaced crossing points.

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

Figure 13 Ideal 'RXEYE' Signal

Mode Register B3: PSAVE - Powersave

When this bit is a '1', the modem will be in a 'powersave' mode in which the internal filters, the Rx Symbol and

Clock extraction circuits and the Tx o/p buffer will be disabled, and the TxOp pin will be connected to Vbias

through a high value resistance. The Xtal Clock oscillator, Rx i/p amplifier and the µC interface logic will

continue to operate.

Setting the PSAVE bit to '0' restores power to all of the chip circuitry. Note that the internal filters - and hence

the TxOp pin in transmit mode - will take about 20 symbol-times to settle after the PSAVE bit is taken from '1'

to '0'.

Mode Register B2: SSIEN - 'S' Symbol IRQ Enable

In receive mode, setting this bit to '1' causes the IRQ bit of the status register to be set to '1' whenever a new

'S' symbol has been received. (The SRDY bit of the Status Register will also be set to '1' at the same time,

and the SVAL bits updated to reflect the received 'S' symbol.)

In transmit mode, setting this bit to '1' causes the IRQ bit of the Status Register to be set to '1' whenever a 'S'

symbol has been transmitted. (The SRDY bit of the Status Register will also be set to '1' at the same time.)

Mode Register B1, 0: SSYM - 'S' Symbol To Be Transmitted

In transmit mode these two bits define the next 'S' symbol to be transmitted. These bits have no effect in

receive mode.

1.5.5.5 Status Register

This register may be read by the µC to determine the current state of the modem.

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

Status Register B7: IRQ - Interrupt Request

This bit is set to '1' by:

The Status Register BFREE bit going from '0' to '1', unless this is caused by a RESET task or by a

change to the Mode Register TXRXN or PSAVE bits.

or

The Status Register IBEMPTY bit going from '0' to '1', unless this is caused by a RESET task or by

changing the Mode Register TXRXN or PSAVE bits.

or

The Status Register DIBOVF bit going from '0' to '1'.

The Status Register SRDY bit being set to '1' (due to a 'S' symbol being received or transmitted) if

the Mode Register SSIEN bit is '1'.

The IRQ bit is cleared to '0' immediately after a read of the Status Register.

If the IRQNEN bit of the Mode Register is '1', then the chip IRQN output will be pulled low (to V ) whenever

SS

the IRQ bit is set to '1', and will go high impedance when the Status Register is read.

Status Register B6: BFREE - Data Block Buffer Free

This bit reflects the availability of the Data Block Buffer and is cleared to '0' whenever a task other than NULL

or RESET is written to the Command Register.

In transmit mode, the BFREE bit will be set to '1' (also setting the Status Register IRQ bit to '1') by the modem

when the modem is ready for the µC to write new data to the Data Block Buffer and the next task to the

Command Register.

In receive mode, the BFREE bit is set to '1' (also setting the Status Register IRQ bit to '1') by the modem when

it has completed a task and any data associated with that task has been placed into the Data Block Buffer.

The µC may then read that data and write the next task to the Command Register.

The BFREE bit is also set to '1' - but without setting the IRQ bit - by a RESET task or when the Mode Register

TXRXN or PSAVE bits are changed.

Status Register B5: IBEMPTY - Interleave Buffer Empty

In transmit mode, this bit will be set to '1' - also setting the IRQ bit - when less than two symbols remain in the

Interleave Buffer. Any transmit task written to the modem after this bit goes to '1' will be too late to avoid a gap

in the transmit output signal.

The bit is also set to '1' by a RESET task or by a change of the Mode Register TXRXN or PSAVE bits, but in

these cases the IRQ bit will not be set.

The bit is cleared to '0' within one symbol time after a task other than NULL or RESET is written to the

Command Register.

Note: When the modem is in transmit mode and the Interleave Buffer is empty, a mid level (half-way between

'+1' and '-1') signal will be sent to the RRC filter.

In receive mode this bit will be '0'.

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

Status Register B4: DIBOVF - De-Interleave Buffer Overflow

In receive mode this bit will be set to '1' - also setting the IRQ bit - when a RHB, RILB, RSID or R4S task is

written to the Command Register too late to allow continuous reception.

The bit is cleared to '0' immediately after reading the Status Register, by writing a RESET task to the

Command Register or by changing the TXRXN or PSAVE bits of the Mode Register.

In transmit mode this bit is '0'.

Status Register B3: CRCERR - CRC Checksum Error

In receive mode this bit will be updated at the end of a SFP, RHB, RILB or RSID task to reflect the result of

the receive CRC check. '0' indicates that the CRC was received correctly, '1' indicates an error. In transmit

mode this bit will be '0'.

Note that this bit should be ignored when an 'Intermediate' block (which does not have an integral CRC) is

received.

The bit is cleared to '0' by a RESET task, or by changing the TXRXN or PSAVE bits of the Mode Register.

Status Register B2: SRDY - 'S' Symbol Ready

In receive mode, this bit is set to '1' whenever an 'S' symbol has been received. The µC may then read the

value of the symbol from the SVAL field of the Status Register. In transmit mode, this bit is set to '1' whenever

an 'S' symbol has been transmitted.

The bit is cleared to '0' immediately after a read of the Status Register, by a RESET task or by changing the

TXRXN or PSAVE bits of the Mode Register.

Status Register B1, B0: SVAL - Received 'S' Symbol Value

In receive mode, these two bits reflect the value of the latest received 'S' symbol. In transmit mode, these two

bits will be '0'.

1.5.5.6 Data Quality Register

In receive mode, the FX929B continually measures the 'quality' of the received signal, by comparing the actual

received waveform over the previous 64 symbol times against an internally generated 'ideal' 4-level FSK

baseband signal.

The result is placed into bits 3-7 of the Data Quality Register for the µC to read at any time, bits 0-2 being

always set to '0'. Figure 14 shows how the value (0-255) read from the Data Quality Register varies with

received signal-to-noise ratio:

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

250

200

150

100

50

DQ

0

8

9

10

11

12

13

14

15

16

S/N dB (Noise in 2 x Symbol Rate Bandwidth)

Figure 14 Typical Data Quality Readingvs S/N

The Data Quality readings are only valid when the modem has successfully acquired signal level and timing

lock for at least 64 symbol times. It is invalid when an AQSC or AQLEV sequence is being performed or when

the LEVRES setting is 'Lossy Peak Detect'. A low reading will be obtained if the PLLBW bits are set to 'Wide'

or if the received signal waveform is distorted in any significant way.

Section 1.6.6 describes how monitoring the Data Quality reading can help improve the overall system

performance in some applications.

1.5.6

CRC, FEC and Interleaving

Cyclic Redundancy Codes

CRC0

This is a six-bit CRC check code used in the Station ID Block. It is calculated by the modem from the first 24

bits of the block ( Bytes 0,1 & 2) as follows:

The 24 bits are considered as the coefficients of a polynomial M(x) of degree 23, such that the msb bit (7) of

23

0

byte 0 is the coefficient of x , and bit 0 of byte 2 is the coefficient of x .

The polynomial F(x) of degree 5 is calculated as being the remainder of the modulo-2 division

6

4

3

x M(x) / (x + x + x + 1 )

5

4

3

2

1

0

The polynomial x + x + x + x + x + x is added (modulo-2) to F(x)

5

The coefficients of F(x) are placed in the 6-bit CRC0 field, such that the coefficient of x corresponds to the

msb of CRC0.

CRC1

This is a sixteen-bit CRC check code contained in bytes 10 and 11 of the Header Block. It is calculated by the

modem from the first 80 bits of the block ( Bytes 0 to 9 inclusive) using the generator polynomial:

16

12

5

x

+ x + x + 1

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FX929B

CRC2

This is a thirty-two-bit CRC check code contained in bytes 8 to 11 of the 'Last' Block. It is calculated by the

modem from all of the data and pad bytes in the Intermediate Blocks and in the first 8 bytes of the Last Block

using the generator polynomial:

32

26

23

22

16

12

11

10

8

7

5

4

2

1

x

+ x + x + x + x + x + x + x + x + x + x + x + x + x + 1

Notes:

In receive mode the CRC2 checksum circuits are initialised on completion of any task other than NULL

or RILB. In transmit mode the CRC2 checksum circuits are initialised on completion of any task other

than NULL, TIB or TLB.

Command Register bit B5 (CRC) allows the user to select between two different forms of the CRC0,

CRC1 and CRC2 checksums. When this bit is set to '1' the CRC generators are initialised to 'all

zeros', as required by RD-LAP systems. When this bit is set to '0' the CRC generators are initialised

to 'all ones' as required by CCITT X25 based systems. It should always be set to '1' for RD-LAP

compatibility, other systems may set this bit as required.

Forward Error Correction

In transmit mode, the FX929B uses a Trellis Encoder to translate the 96 bits (12 bytes) of a 'Header',

'Intermediate' or 'Last' Block or the 30 bits of a Station ID Block into a 66 or 22-symbol sequence which

includes FEC information.

In receive mode, the FX929B decodes the received 22 or 66 symbols of a block into 30 or 96 bits of binary

data using a 'Soft Decision' Viterbi algorithm to perform decoding and error correction.

Interleaving

The 66 symbols of a 'Header', 'Intermediate' or 'Last' block are interleaved by the modem before transmission

(and before the 'S' symbols are added) to give protection against the effects of noise bursts and short fades.

The 22 symbols of a 'Station ID' Block are not interleaved.

In receive mode, the FX929B de-interleaves the received symbols after stripping out the 'S' symbols and prior

to decoding.

1.5.7

Transmitted Symbol Shape

Bit 4 of the Command Register (TXIMP) affects the transmit baseband signal and the receive signal

equalisation as follows.

If the TXIMP bit is '0', then the transmit baseband signal is generated by feeding full-width 4-level symbols into

the RRC lowpass filter, and the receive signal equalisation is optimised for this type of signal. With this setting

the FX929B is compatible with FX929A devices.

If the TXIMP bit is set to '1', then impulses, rather than full-width symbols, are fed into the RRC filter when in

Tx mode, and the receive signal equalisation is suitably adjusted in Rx mode.

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FX929B

Figure 15a Input Signal to RRC Filter iTnx Mode for TXIMP = 0 and 1

Figure 15b Tx Signal Eye TXIMP = 0

Figure 15c Tx Signal Eye TXIMP = 1

Note that setting TXIMP to '1' affects the Tx output signal level as shown in section 1.7.1 and the table below:

TXIMP = 0

TXIMP = 1

Nominal voltage difference between continuous '+3' and

continuous '-3' symbol outputs.

0.157 V_DD

Nominal Vp-p for continuous '+3 +3 -3 -3..' symbol

pattern

0.20 V_DD

0.22 V_DD

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4-Level FSK Modem Data Pump

FX929B

1.6

Application Notes

1.6.1

Transmit Frame Examples

The operations needed to transmit a single Frame consisting of Symbol and Frame Sync sequences, Station

ID block, and one each Header, Intermediate and Last blocks are shown below:

1.

Ensure that the Control Register has been loaded with a suitable CKDIV value, that the IRQNEN

and TXRXN bits of the Mode Register are '1', the RXEYE, PSAVE and SSIEN bits are '0' and the

INVSYM bit is set appropriately.

2.

3.

Read the Status Register to ensure that the BFREE bit is '1', then write 6 Symbol Sync bytes to the

Data Block Buffer and a T24S task to the Command Register.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the IBEMPTY bit should be '0'.

4.

5.

Write 6 Frame Sync bytes to the Data Block Buffer and a T24S task to the Command Register.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the IBEMPTY bit should be '0'.

6.

7.

Write 3 Station ID bytes to the Data Block Buffer and a TSID task to the Command Register.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the IBEMPTY bit should be '0'.

8.

9.

Write 10 Header Block bytes to the Data Block Buffer and a THB task to the Command Register.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the IBEMPTY bit should be '0'.

10.

11.

Write 12 Intermediate Block bytes to the Data Block Buffer and a TIB task to the Command

Register.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the IBEMPTY bit should be '0'.

12.

13.

Write 8 Last Block bytes to the Data Block Buffer and a TLB task to the Command Register.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the IBEMPTY bit should be '0'.

14.

Wait for another interrupt from the modem, read the Status Register; the IRQ, BFREE and

IBEMPTY bits should be '1'.

Note: The final symbol of the frame will start to appear approximately 2 symbol times after the Status Register

IBEMPTY bit goes to '1'; a further 16 symbol times should be allowed for the symbol to pass completely

through the RRC filter.

Note: The SSYM bits of the Mode Register may be altered at any time to change the transmitted 'S' symbols.

If a timing reference is required, then setting the Mode Register SSIEN bit to '1' will cause a µC interrupt after

every 'S' symbol transmitted - in which case the µC will have to distinguish between interrupts caused by the

BFREE bit going to '1', and those caused by the SRDY bit being set to '1'.

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FX929B

Figures 16a and 16b illustrate the host µC routines needed to send a single Frame consisting of Symbol and

Frame Sync patterns, a Station ID block, a Header block, any number of Intermediate blocks and one Last

block. It is assumed that the Tx Interrupt Service Routine (Figure 16b) is called whenever the FX929B's IRQN

output line goes low.

Figure 16a Transmit Frame Example Flowchart, Main Program

Note that the RESET command in Figure 16a and the practice of disabling the FX929B's IRQN output when

not needed are not essential but can eliminate problems during debugging and if errors occur in operation.

Note also that the CRC and TXIMP bits should be set appropriately whenever a byte is written to the

Command Register.

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FX929B

Figure 16b Tx Interrupt Service Routine

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FX929B

1.6.2

Receive Frame Examples

The operations needed to receive a single Frame consisting of Symbol and Frame Sync sequences, Station ID

block and one each Header, Intermediate and Last blocks are shown below;

1.

Ensure that the Control Register has been loaded with suitable CKDIV, FSTOL, LEVRES and

PLLBW values, and that the IRQNEN bit of the Mode Register is '1', the TXRXN, RXEYE, PSAVE

and SSIEN bits are '0', and the INVSYM bit is set appropriately.

2.

3.

4.

Wait until the received carrier has been present for at least 8 symbol times (see Section 1.6.3).

Read the Status Register to ensure that the BFREE bit is '1'.

Write a byte containing a SFP task with the AQSC and AQLEV bits set to '1' to the Command

Register.

5.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the CRCERR and DIBOVF bits should be '0'.

6.

7.

8.

Read 3 Station ID bytes from the Data Block Buffer.

Write a RHB task to the Command Register.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the DIBOVF bit '0'.

9.

Check that the CRCERR bit of the Status Register is '0' and read 10 Header Block bytes from the

Data Block Buffer.

10

Write a RILB task to the Command Register.

11.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the DIBOVF bit '0'.

12.

13.

14.

Read 12 Intermediate Block bytes from the Data Block Buffer.

Write a RILB task to the Command Register.

Wait for an interrupt from the modem, read the Status Register; the IRQ and BFREE bits should be

'1' and the DIBOVF bit '0'.

15.

Check that the CRCERR bit of the Status Register is '0' and read the 8 Last Block bytes from Data

Buffer.

Note: The value of the latest 'S' symbol received will be contained in the SVAL bits each time that the Status

Register is read. If desired, the Mode Register SSIEN bit may be set to '1', which will cause a µC interrupt

after every 'S' symbol is received - in which case the µC will have to distinguish between interrupts caused by

the BFREE bit going to '1', and those caused by the SRDY bit being set to '1'.

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4-Level FSK Modem Data Pump

FX929B

Figures 17a and 17b illustrate the host µC routines needed to receive a single Frame consisting of Symbol and

Frame Sync patterns, a Station ID block, a Header block, any number of Intermediate blocks and one Last

block. It is assumed that the Rx Interrupt Service Routine (Figure 17b) is called whenever the FX929B's IRQN

output line goes low.

Figure 17a Receive Frame Example Flowchart, Main Program

Note that the RESET command in Figure 17a and the practice of disabling the FX929B's IRQN output when

not needed are not essential but can eliminate problems during debugging and if errors occur in operation.

Note also that the CRC and TXIMP bits should be set appropriately whenever a byte is written to the

Command Register.

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4-Level FSK Modem Data Pump

FX929B

Figure 17b Rx Interrupt Service Routine

Note: This routine assumes that the number of Intermediate blocks in the Frame is contained within the

Header Block data.

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4-Level FSK Modem Data Pump

FX929B

1.6.3

Clock Extraction and Level Measurement Systems

The FX929B is intended for use in systems where:

-

The Symbol Sync pattern is transmitted immediately on start-up of the transmitter, before the first

Frame Sync pattern (see Figure 18).

A Base Station may remain powered up indefinitely, transmitting concatenated Frames without

intervening Symbol Sync patterns (each Frame starting with the Frame Synch pattern and symbol

timing being maintained from one Frame to the next).

-

A receiving modem may be switched onto a channel before the distant transmitter has started up, or

may be switched onto a channel where the transmitting station is already sending concatenated

Frames.

Whenever the receiving modem is enabled or switched onto a channel it needs to establish the received

symbol levels and timing and look for a Frame Sync pattern in the incoming signal. This is best done by the

following procedure.

1.

2.

Ensure that the Control Register's PLLBW bits are set to 'Wide' and the LEVRES bits to 'Level Track'.

Wait until a received carrier has been present for 8 symbol times. This 8-symbol delay gives time for

the received signal to propagate through the modem's RRC filter and can usefully be included in the

radio's carrier detect circuitry.

3.

4.

Write a SFS or SFP task to the Command Register with the AQSC and AQLEV bits set to '1'.

When the modem interrupts to signal that it has recognised a Frame Sync pattern (or completed the

SFP task) then change the PLLBW bits to 'Medium'.

Once the receiving modem has achieved level and symbol timing synchronisation with a particular channel -

as evidenced by recognition of a Frame Sync pattern - then subsequent concatenated Frames can be read by

simply issuing SFS or SFP tasks at appropriate times, keeping the ASQSC and AQLEV bits at zero, and the

PLLLBW and LEVRES bits at their current 'Medium' and 'Level Track' settings.

noise

Frame Sync

rest of frame

Symbol Sync

Received signal

from FM discriminator

to Modem :

8-symbol delay

Set AQSC and AQLEV bits

to start acquisition sequences :

Level Measurement and

Clock Extraction circuits :

Increasing accuracy and lengthening response times

Figure 18 Acquisition Sequence Timing (Transmitter Power-Up)

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4-Level FSK Modem Data Pump

FX929B

It is also possible to use the modem in a non-standard system where there is an indeterminate delay between

the transmitter start-up and the Symbol Sync pattern, or where a receive carrier detect signal is not available

to the controlling mC, or where the transmitting terminal can send separate unsynchronised Frames. In these

cases each Frame should be preceded by a Symbol Sync pattern which should be extended to about 100

symbols, and the procedure given in paragraphs (1) to (4) above used at all times.

Setting the AQSC and AQLEV bits to '1' triggers the modem's automatic Symbol Clock Extraction and Level

Measurement acquisition sequences, which are designed to measure the received symbol timing, amplitude

and dc offset as quickly as possible before switching to more accurate - but slower - measurement modes.

These acquisition sequences act very quickly if triggered at the start of a received Symbol Sync pattern (as

shown in Figure 18), but will still function correctly - although more slowly - if started any time during a normal

Frame, as when the receiver is switched onto a channel where the transmitter is operating continuously.

The automatic AQLEV Level Measurement acquisition sequence starts with the level measurement circuits

being put into 'Clamp' mode for one symbol time to set the voltages on the DOC pins to some point within the

range of the received signal excursions. The level measurement circuits are then automatically set to 'Lossy

Peak Detect' mode for 15 symbol times, then to 'Slow Peak Detect' until a received Frame Sync pattern is

recognised, after which the sequence ends and the level measurement circuit mode reverts to the mode set by

the LEVRES bits of the Control Register (normally 'Level Track').

The peak detectors used in both 'Slow' and 'Lossy Peak Detect' modes include additional low pass filtering of

the received signal which greatly reduces the effect of pattern noise on the reference voltages held on the

external DOC capacitors, but means that pairs of '+3' (and '-3') symbols need to be received to establish the

correct levels. 2 pairs of '+3' and two pairs of '-3' symbols received after the start of an AQLEV sequence are

sufficient to set the levels on the DOC capacitors to their correct levels.

The automatic AQSC Symbol Clock acquisition sequence sets the PLL to 'Extra Wide Bandwidth' mode for 16

symbol times (this mode is not one of those which can be selected by the Control Register PLLBW bits) then

changes to 'Wide' bandwidth. After 45 symbol times the PLL mode will revert to that set by the Control

Register PLLBW bits.

1.6.4

AC Coupling

For a practical circuit, ac coupling from the modem's transmit output to the frequency modulator and between

the receiver's frequency discriminator and the receive input of the modem may be desired. There are,

however, two problems:

Firstly, ac coupling of the signal degrades the Bit Error Rate performance of the modem. The following graph

illustrates the effect of ac coupling on typical bit error rates at 4800 symbols/sec (without FEC) for reasonably

random data with differing degrees of ac coupling:

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

1E-1

1E-2

1E-3

1E-4

Tx & Rx DC coupled

Tx 5Hz, Rx DC

Tx 5Hz, Rx 5Hz

Tx 5Hz, Rx 10Hz

4

5

6

7

8

9

10

11

12

13

14

S/N dB (Noise in 20 to 9600Hz band)

Figure 19 Effect of AC Coupling on BER without FEC

Secondly, any ac coupling at the receive input will transform any step in the voltage at the discriminator output

to a slowly decaying pulse which can confuse the modem's level measuring circuits. As illustrated in Figure 20

below, the time for this step to decay to 37% of its original value is 'RC' where:

RC = 1/( 2 x p x the 3dB cut-off frequency of the RC network )

which is 32 msec, or 153 symbol times at 4800 symbols/sec, for a 5Hz network.

Step input

to RC circuit

100%

Output of

37%

RC circuit

T=RC

Figure 20 Decay Time - AC Coupling

In general, it will be best to dc couple the receiver discriminator to the modem, and to ensure that any ac

coupling to the transmitter's frequency modulator has a -3dB cut-off frequency of no higher than 5Hz (for 4800

symbols/sec).

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

1.6.5

Radio Performance

The maximum data rate that can be transmitted over a radio channel using these modems depends on:

-

RF channel spacing.

Allowable adjacent channel interference.

Symbol rate.

Peak carrier deviation (modulation index).

Tx and Rx reference oscillator accuracies.

Modulator and demodulator linearity.

Receiver IF filter frequency and phase characteristics.

Use of error correction techniques.

Acceptable error rate.

As a guide, 4800 symbols/sec can be achieved - subject to local regulatory requirements - over a system with

12.5kHz channel spacing if the transmitter frequency deviation is set to ±2.5kHz peak for a repetitive '+3 +3 -

3 -3 ....' pattern and the maximum difference between transmitter and receiver 'carrier' frequencies is less

than 2400Hz.

The modulation scheme employed by these modems is designed to achieve high data throughput by exploiting

as much as possible of the RF channel bandwidth. This does, however, place constraints on the performance

of the radio. In particular, attention must be paid to:

-

Linearity, frequency and phase response of the Tx Frequency Modulator. For a 4800

symbols/sec system, the frequency response should be within ±2dB over the range 3Hz to

5kHz, relative to 2400Hz.

-

The bandwidth and phase response of the receiver's IF filters.

Accuracy of the Tx and Rx reference oscillators, as any difference will shift the received signal

towards the skirts of the IF filter response and cause a dc offset at the discriminator output.

Viewing the received signal eye - using the Mode Register RXEYE function - gives a good indication of the

overall transmitter/receiver performance.

Figure 21 Typical Connections Between Radio and FX929B

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4-Level FSK Modem Data Pump

FX929B

1.6.6

Received Signal Quality Monitor

In applications where the modem has to monitor a long transmission containing a number of concatenated

Frames, it is recommended that the controlling software includes a function which regularly checks that the

modem is still receiving a good data signal, and triggers a re-acquisition and possibly changes to another

channel if a problem is encountered. This strategy has been shown to improve the system's overall

performance in situations where fading, large noise bursts, severe co-channel interference or loss of the

received signal for long periods are likely to occur.

Such a function can be simply implemented by regularly reading the Data Quality Register, which gives a

measure of the overall quality of the received signal, as well as the current effectiveness of the modem's clock

extraction and level measurement systems. Experience has shown that if two consecutive DQ readings are

both less than 50 then it is worth instructing the FX929B to re-acquire the received signal levels and timing

once it has been established that the received carrier level is satisfactory. This re-acquisition should follow the

normal procedure given in section 1.6.3.

The intervals between Data Quality readings is not critical, but should be a minimum of 64 symbol times

except for the first reading made after triggering the AQSC and AQLEV automatic acquisition sequences,

which should be delayed for about 250 symbol times.

A suitable algorithm is illustrated below.

Figure 22 Received Signal Quality Monitor Flowchart

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4-Level FSK Modem Data Pump

FX929B

1.7

Performance Specification

1.7.1

Electrical Performance

Absolute Maximum Ratings

Exceeding these maximum ratings can result in damage to the device.

Min.

Max.

7.0

V_DD+ 0.3

+30

Units

V

mA

Supply (V_DD- V_SS

)

-0.3

-30

-20

Voltage on any pin to V_SS

Current into or out of V_DDand V_SSpins

Current into or out of any other pin

+20

P4 Package

Total Allowable Power Dissipation at Tamb = 25°C

... Derating

Storage Temperature

Operating Temperature

Min.

Max.

800

13

+125

+85

Units

mW

mW/°C

°C

-55

-40

°C

D2 Package

Total Allowable Power Dissipation at Tamb = 25°C

... Derating

Storage Temperature

Operating Temperature

Min.

Max.

800

13

+125

+85

Units

mW

mW/°C

°C

-55

-40

°C

D5 Package

Total Allowable Power Dissipation at Tamb = 25°C

... Derating

Storage Temperature

Operating Temperature

Min.

Max.

550

9

+125

+85

Units

mW

mW/°C

°C

-55

-40

°C

Operating Limits

Correct operation of the device outside these limits is not implied.

Notes

Min.

3.0

Max.

5.5

Units

V

Supply (V_DD- V_SS

)

Operating Temperature

Symbol Rate

Xtal Frequency

-40

2400

1.0

+85

9600

10.0

°C

Symbols/sec

MHz

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4-Level FSK Modem Data Pump

FX929B

Operating Characteristics

For the following conditions unless otherwise specified:

Xtal Frequency = 4.9152MHz, Symbol Rate = 4800 symbols/sec,

Noise Bandwidth = 0 to 9600Hz, V_DD= 3.3V to 5.0V, Tamb = - 40°C to +85°C.

Notes

Min.

Typ.

Max.

Units

DC Parameters

I_DD

(V_DD= 5.0V)

(V_DD= 3.3V)

(Powersave Mode, V_DD= 5.0V)

(Powersave Mode, V_DD= 3.3V)

1

4.0

2.5

1.5

0.6

10.0

6.3

mA

AC Parameters

Tx Output

TXOP Impedance

2

3

4

1.0

1.1

2.5

1.2

1.32

+0.25

kW

Signal Level TXIMP = 0

Signal Level TXIMP = 1

Output DC Offset wrt V_DD/2

0.8

0.88

-0.25

V pk-pk

V

Rx Input

RXIN Impedance (at 100Hz)

RXIN Amp Voltage Gain (I/P = 1mVrms at 100Hz)

Input Signal Level

10.0

300

1.0

MW

V/V

V pk-pk

V

5

0.7

-0.5

1.3

+0.5

DC Offset wrt V_DD/2

Xtal/Clock Input

'High' Pulse Width

'Low' Pulse Width

Input Impedance (at 100Hz)

Inverter Gain (I/P = 1mVrms at 100Hz)

6

40.0

10.0

20.0

ns

MW

dB

µC Interface

Input Logic "1" Level

Input Logic "0" Level

Input Leakage Current (Vin = 0 to V_DD

Input Capacitance

Output Logic "1" Level (l_OH= 120µA)

Output Logic "0" Level (l_OL= 360µA)

'Off' State Leakage Current (Vout = V_DD

7, 8

8

70%

5.0

V_DD

µA

30%

+5.0

)

10.0

pF

92%

V_DD

µA

8, 9

9

8%

10.0

)

Notes:

1. At 25°C. Not including any current drawn from the modem pins by external circuitry other

than the Xtal oscillator.

2. Small signal impedance, at V_DD= 5.0V and Tamb = 25°C.

3. Measured after the external RC filter (R4/C5) for a "+3 +3 -3 -3...." symbol sequence, at V_DD

= 5.0V and Tamb = 25°C (Tx output level is proportional to V_DD).

4. Measured at the TXOP pin with the modem in the Tx idle mode.

5. For optimum performance, measured at RXFB pin, for a "...+3 +3 -3 -3..." symbol sequence,

at V_DD= 5.0V and Tamb = 25°C, TXIMP = 0 or 1. The optimum level and DC offset values

are proportional to V_DD

.

6. Timing for an external input to the CLOCK/XTAL pin.

7. WRN, RDN, CSN, A0 and A1 pins.

8. D0 - D7 pins.

9. IRQN pin.

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4-Level FSK Modem Data Pump

FX929B

Notes

Min.

Typ.

Max.

Units

mC Parallel Interface Timings (ref. Figure 23)

t_ACSL

t_AH

Address valid to CSN low time

Address hold time

0

ns

t_CSH

CSN hold time

0

ns

t_CSHI

t_CSRWL

t_DHR

t_DHW

t_DSW

t_RHCSL

t_RACL

t_RARL

t_RL

CSN high time

CSN to WRN or RDN low time

Read data hold time

Write data hold time

Write data setup time

RDN high to CSN low time (write)

Read access time from CSN low

Read access time from RDN low

RDN low time

RDN high to D0-D7 3-state time

WRN high to CSN low time (read)

WRN low time

10

6.0

0

90.0

0

clock cycles

ns

11

175

145

200

t_RX

t_WHCSL

t_WL

50.0

0

200

Notes:

10. Xtal/Clock cycles at the XTAL/CLOCK pin.

11. With 30pF max to V_SSon D0 - D7 pins.

Figure 23 mC Parallel Interface Timings

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D/929B/1

4-Level FSK Modem Data Pump

FX929B

1E-1

1E-2

BER with FEC

BER without FEC

1E-3

BER

1E-4

1E-5

1E-6

8

9

10

11

12

13

14

15

16

S/N dB (Noise in 2 x Symbol Rate Bandwidth)

Figure 24 Typical Bit Error Rate With and Without FEC

Measured under nominal working conditions, LEVRES bits set to ‘Level Track’ or ‘Slow Peak Detect’ and

PLLBW bits set to ‘Medium’ or ‘Narrow’ Bandwidth, Command Register TXIMP bit set to 0 or 1 (same for Tx

and Rx devices), with pseudo-random data.

Note: S/N calculated as 20 ´ LOG ( Signal Voltage ¸ Noise Voltage)

10

Where Signal Voltage is the measured rms voltage of a random 4-level signal.

Noise Voltage is the rms voltage of a flat Gaussian noise signal having a bandwidth from a

few Hz to twice the symbol rate (e.g. to 9600Hz when measuring a 4800 symbol/sec system).

Both signals are measured at the same point in the test circuit.

ã 1997 Consumer Microcircuits Limited

45

D/929B/1

4-Level FSK Modem Data Pump

FX929B

1.7.2

Packaging

Figure 25 D2 Mechanical Outline: Order as part no. FX929BD2

Figure 26 D5 Mechanical Outline: Order as part no. FX929BD5

ã 1997 Consumer Microcircuits Limited

46

D/929B/1

4-Level FSK Modem Data Pump

FX929B

Figure 27 P4 Mechanical Outline: Order as part no. FX929BP4

Handling precautions: This product includes input protection, however, precautions should be taken to

prevent device damage from electro-static discharge. CML does not assume any responsibility for the

use of any circuitry described. No IPR or circuit patent licences are implied. CML reserves the right at

any time without notice to change the said circuitry and this product specification. CML has a policy of

testing every product shipped using calibrated test equipment to ensure compliance with this product

specification. Specific testing of all circuit parameters is not necessarily performed.

CONSUMER MICROCIRCUITS LIMITED

1 WHEATON ROAD

WITHAM - ESSEX

CM8 3TD - ENGLAND

Telephone:

Telefax:

e-mail:

+44 1376 513833

+44 1376 518247

sales@cmlmicro.co.uk

http://www.cmlmicro.co.uk


型号：	FX929BD2
厂家：	CML MICROCIRCUITS
描述：	Modem-Support Circuit, CMOS, PDSO24, 电信光电二极管电信集成电路
文件：	总47页 (文件大小：1631K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

FX929BD2 [CMLMICRO]

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