MAX7349AWG_技术文档

19-3556; Rev 5; 5/07

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

General Description

Features

The MAX7347/MAX7348/MAX7349 I²C interfaced periph-

erals provide microprocessors with management of up to

64 key switches. Key inputs are monitored statically, not

dynamically scanned, to ensure low-EMI operation. The

MAX7347 can monitor up to 24 switches, the MAX7348

can monitor up to 40 switches, and the MAX7349 can

monitor up to 64 switches. The switches can be metallic

or resistive (carbon) up to 1kΩ.

♦ 400kbps, 5.5V-Tolerant 2-Wire Serial Interface

♦ 2.4V to 3.6V Operation

♦ Monitor Up to 64 Keys (MAX7349),

40 Keys (MAX7348), or 24 Keys (MAX7347)

♦ FIFO Queues Up to 8 Debounced Key Events

♦ Key Debounce Time User Configurable from 9ms

The key controller debounces and maintains a FIFO of

key-press events (including autorepeat, if enabled). An

interrupt (INT) output can be configured to alert key

presses either as they occur, or at maximum rate.

to 40ms

♦ Key Autorepeat Rate and Delay User Configurable

♦ Low-EMI Design Uses Static Matrix Monitoring

The MAX7348/MAX7349 feature a tone generator to

generate automatic key-click sounds or alarm tones

under processor control.

♦ Hardware Interrupt on Each Debounced Event or

FIFO Level, or at End of Definable Time Period

♦ Up to Six Open-Drain Logic Outputs Available

The sounder frequencies cover the 5th musical octave

(523.25Hz to 987.77Hz), plus seven other musical

notes up to 2637Hz. The output can also be pro-

grammed to be high or low for the sound duration to

operate an electronic sounder, relay, or lamp.

Capable of Driving LEDs

♦ Sounder Output Generates Automatic Key Clicks

♦ 14 Programmable Musical Sounder Frequencies

♦ Continuous or Programmable Sounder Duration

The MAX7347 is offered in 16-pin QSOP and TQFN

packages. The MAX7348 is offered in a 20-pin QSOP

package. The MAX7349 is available in 24-pin QSOP and

TQFN packages. The MAX7347/MAX7348/MAX7349

operate over the -40°C to +125°C temperature range.

♦ Easy Automatic Single-Tone and Dual-Tone Alarm

Sound Generation

♦ Four I²C Address Choices

♦ Selectable 2-Wire Serial Bus Timeout

Applications

♦ Under 10µA Shutdown Current

Medical Instruments

Instrumentation Panels

Security and Access

Industrial Controls

Ordering Information

PKG

PIN-

PACKAGE

PART

TEMP RANGE

CODE

Pin Configurations appear at end of data sheet.

E16-4

T1644-4

E20-1

MAX7347AEE+ -40°C to +125°C 16 QSOP

MAX7347ATE+ -40°C to +125°C 16 TQFN-EP*

MAX7348AEP+ -40°C to +125°C 20 QSOP

MAX7349AEG+ -40°C to +125°C 24 QSOP

MAX7349ATG+ -40°C to +125°C 24 TQFN-EP*

Typical Application Circuit

INPUT

2.4V TO 3.6V

E24-1

8

MAX7349

V+

COL_

SWITCH

ARRAY, UP

TO 64

T2444-4

+Denotes lead-free package.

*EP = Exposed paddle.

SWITCHES

ROW_

SCL

SDA

ALERT

INT

PIEZO

TRANSDUCER

AD0

GND

SOUNDER

________________________________________________________________ Maxim Integrated Products

1

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

ABSOLUTE MAXIMUM RATINGS

(All voltages referenced to GND.)

Continuous Power Dissipation (T = +70°C)

A

V+ ............................................................................-0.3V to +4V

COL2/PORT2–COL7/PORT7 ....................................-0.3V to +4V

SDA, SCL, AD0, ALERT, INT....................................-0.3V to +6V

All Other Pins................................................-0.3V to (V+ + 0.3V)

DC Current on COL2/PORT2–COL7/PORT7 ......................25mA

DC Current on SOUNDER ................................................ 25mA

GND Current .......................................................................80mA

16-Pin QSOP (derate 8.3mW/°C above +70°C)...........666mW

16-Pin TQFN (derate 16.9mW/°C above +70°C).......1349.1mW

20-Pin QSOP (derate 9.1mW/°C above +70°C)...........727mW

24-Pin QSOP (derate 9.5mW/°C above +70°C)...........761mW

24-Pin TQFN (derate 20.8mW/°C above +70°C).......1666.7mW

Operating Temperature Range (T

to T ) ...-40°C to +125°C

MAX

MIN

Junction Temperature......................................................+150°C

Storage Temperature Range.............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS

(V+ = 2.4V to 3.6V, T = T

A

to T

, unless otherwise noted. Typical values are at V+ = 3.3V, T = +25°C.) (Notes 1, 2)

MAX A

MIN

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

3.6

UNITS

V

Operating Supply Voltage

Operating Supply Current

Shutdown Supply Current

V+

I+

2.4

All key switches open

75

100

10

µA

I

6.44

µA

SH

V+ -

0.45

SOUNDER Output High Voltage

V

I = 10mA

SOURCE

V

OHBUZ

SOUNDER Output Low Voltage

SOUNDER Frequency Accuracy

Key-Switch Source Current

Key-Switch Source Voltage

Key-Switch Resistance

V

I

= 10mA

SINK

0.15

V

%

OLBUZ

T

= +25°C, V+ = 3.3V

1.2

28

A

8/MAX7349

I

40

0.65

1

µA

V

KEY

V

0.35

KEY

R

(Note 3)

kΩ

µs

Startup Time from Shutdown

t

57

200

START

Output Low Voltage

COL2/PORT2 to COL7/PORT7,

INT Output

V

I

= 10mA

0.15

V

OLPORT

SINK

Input voltage ≤ V+

Input voltage > V+

-1

-5

+1

+5

Input Leakage Current Alert

µA

Input High Voltage ALERT

Input Low Voltage ALERT

V

2.2

V

IH

V

0.8

68

IL

SERIAL-INTERFACE SPECIFICATIONS

Serial Bus Timeout

t

With bus timeout enabled

20

ms

V

OUT

Input High Voltage

SDA, SCL, AD0

V

2.2

IH

Input Low Voltage

SDA, SCL, AD0

V

0.6

V

IL

Input voltage ≤ V+

Input voltage > V+

-1

-5

+1

+5

Input Leakage Current

SDA, SCL, AD0

µA

2

_______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

2

I C TIMING CHARACTERISTICS

(V+ = 2.4V to 3.6V, T = T

A

to T

, unless otherwise noted. Typical values are at V+ = 3.3V, T = +25°C.) (Notes 1, 2)

MAX A

MIN

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

Input Capacitance

(SCL, SDA, AD0)

C

(Notes 3, 4)

10

pF

IN

With bus timeout enabled

With bus timeout disabled

0.05

0

400

SCL Serial Clock Frequency

f

kHz

µs

SCL

BUF

Bus Free Time Between a STOP

and a START Condition

t

1.3

0.6

Hold Time (Repeated) START

Condition

t

µs

HD, STA

Repeated START Condition

Setup Time

t

0.6

µs

SU, STA

STOP Condition Setup Time

Data Hold Time

t

µs

ns

µs

SU, STO

t

(Note 5)

0.9

HD, DAT

Data Setup Time

t

100

1.3

0.7

SU, DAT

SCL Clock Low Period

SCL Clock High Period

t

LOW

t

HIGH

Rise Time of Both SDA and SCL

Signals, Receiving

20 +

t

(Notes 3, 4)

300

ns

R

0.1C

b

Fall Time of Both SDA and SCL

Signals, Receiving

20 +

0.1C

t

F

b

20 +

0.1C

Fall Time of SDA Transmitting

t

(Notes 3, 6)

(Notes 3, 7)

(Note 3)

250

50

ns

pF

F.TX

b

Pulse Width of Spike Suppressed

t

SP

Capacitive Load for Each Bus

Line

C

400

b

Note 1: All parameters are tested at T = +25°C. Specifications over temperature are guaranteed by design.

A

Note 2: All digital inputs at V+ or GND.

Note 3: Guaranteed by design.

Note 4: C = total capacitance of one bus line in pF. t and t measured between 0.8V and 2.1V.

b

R

F

Note 5: A master device must provide a hold time of at least 300ns for the SDA signal (referred to V of the SCL signal) to bridge

IL

the undefined region of SCL’s falling edge.

Note 6: I

≤ 6mA. C = total capacitance of one bus line in pF. t and t measured between 0.8V and 2.1V.

Note 7: Input filters on the SDA, SCL, and AD0 inputs suppress noise spikes less than 50ns.

SINK

b R F

_______________________________________________________________________________________

3

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Typical Operating Characteristics

(V+ = 3.3V, T = +25°C, unless otherwise noted. Supply range for V+ is 2.4V to 3.6V. Temperature range is -40°C to +125°C.)

A

GPO OUTPUT LOW VOLTAGE

vs. SINK CURRENT

GPO OUTPUT LOW VOLTAGE

vs. SINK CURRENT

GPO OUTPUT LOW VOLTAGE

vs. SINK CURRENT

300

250

200

150

100

50

300

250

200

150

100

50

300

250

200

150

100

50

V+ = 2.4V

V+ = 3V

V+ = 3.6V

T

= +125°C

A

T

= +125°C

A

T

= +125°C

A

T

= -40°C

A

T

= -40°C

A

T

= -40°C

A

T

= +25°C

A

T

A

= +25°C

T

= +25°C

A

0

5

10

15

20

25

0

5

10

15

(mA)

20

25

3.6

0

5

10

15

(mA)

20

25

I

(mA)

I

SINK

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

KEY-SWITCH SOURCE CURRENT

vs. SUPPLY VOLTAGE

SOUNDER FREQUENCY

vs. SUPPLY VOLTAGE

90

85

80

75

70

65

60

55

50

45

40

30

29

28

27

26

25

24

886

884

882

880

878

876

874

COL0 = GND

SOUNDER FREQUENCY

CONFIGURED FOR 880Hz

T

= +25°C

T

= -40°C

A

T

= +125°C

T

= -40°C

A

8/MAX7349

T

= +25°C

A

T

= +25°C

A

T

= +125°C

A

T

= -40°C

A

T

= +125°C

A

2.4

2.6

2.8

3.0

3.2

3.4

3.6

2.4

2.6

2.8

3.0

3.2

3.4

2.4

2.7

3.0

3.3

3.6

SUPPLY VOLTAGE (V)

OSCILLATOR FREQUENCY

vs. SUPPLY VOLTAGE

OSCILLATOR FREQUENCY

vs. TEMPERATURE

SOUNDER OUTPUT

MAX7347 toc07

65

64

63

62

61

60

65

64

63

62

61

60

3V

V

SOUNDER

1V/div

0V

200μs/div

2.4

2.7

3.0

3.3

-40

10

60

110

SUPPLY VOLTAGE (V)

TEMPERATURE (°C)

4

_______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Pin Description

NAME

FUNCTION

MAX7347 MAX7347

MAX7349 MAX7349

MAX7348

(QSOP)

(TQFN)

(QSOP)

(TQFN)

1

2

15

16

1

2

3

23

24

1

ROW0

ROW1

ROW2

ROW3

ROW4

ROW5

ROW6

ROW7

Row Input from Key Matrix. Leave open circuit if unused.

3

4

2

4

5

2

5

3

7

8

5

6

4

8

9

6

7

5

9

10

11

14

15

16

18

20

21

22

7

8

6

10

11

12

13

15

17

18

19

8

9

7

11

12

13

15

17

18

19

COL2/PORT2 Column Output to Key Matrix or GPO

10

11

12

13

14

15

8

COL1

COL0

GND

SDA

SCL

Column Output to Key Matrix

Ground

9

10

11

12

13

2

I C-Compatible Serial Data I/O

2

I C-Compatible Serial Clock Input

INT

Active-Low Interrupt Output. Output is open drain.

Positive Supply Voltage. Bypass V+ to GND with a

0.047µF or higher ceramic capacitor.

16

14

20

23

20

V+

—

5

6

7

3

4

COL3/PORT3 Column Output to Key Matrix or GPO

COL4/PORT4 Column Output to Key Matrix or GPO

Sounder Driver Output. Typically connect a piezo-ceramic

—

14

16

17

19

14

16

SOUNDER sounder or other transducer from this output to ground.

Output is push-pull.

Address Input 0. Sets device slave address. Connect to

AD0

GND, V+, SDA, or SCL to give four logic combinations.

See Table 3.

—

1

22

9

COL7/PORT7 Column Output to Key Matrix or GPO

COL6/PORT6 Column Output to Key Matrix or GPO

COL5/PORT5 Column Output to Key Matrix or GPO

12

13

24

10

21

ALERT

Alert Input. Connect to GND or V+ if unused.

Exposed Paddle. Internally connected to GND. Connect to

a large ground plane to maximize thermal performance.

—

EP

—

EP

The piezo sounder controller generates a variety of

audio tones. Tones are programmable for frequency

and duration, and may be intermittent, two tone, or con-

tinuous. The piezo sounder controller can be config-

ured to deliver an automatic, customizable sound on

every key press to provide a udible key-click feedback.

Detailed Description

The MAX7347/MAX7348/MAX7349 are microprocessor

peripherals that combine a low-noise key-switch inter-

face with a piezo sounder controller. Up to 64 key

switches can be monitored and debounced with optional

autorepeat, and the key events are presented in an

eight-deep FIFO. Key-switch functionality can be traded

to provide up to one (MAX7347), three (MAX7348), or six

(MAX7349) open-drain logic outputs. (Table 1).

Interrupt requests can be configured to be issued on

every key-press event, or can be limited to a maximum

rate to prevent overloading the microprocessor with

_______________________________________________________________________________________

5

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Table 1. Product Features Table

KEY-

MAXIMUM

KEY

SWITCHES

PACKAGE-

PINS

INT

OUTPUT

SCAN

SLAVE

IDs

SOUNDER

SLAVE IDs

SOUNDER

OUTPUT

ALERT

INPUT

PART

GPOs

MAX7349

MAX7348

MAX7347

24

20

16

64

40

24

Yes

4

Yes

—

6 + 1 (INT)

3 + 1 (INT)

1 + 1 (INT)

Yes

—

1 fixed

—

too many interrupts. The key-switch status can be

checked at any time by reading the key-switch FIFO. A

1-byte read access returns both the first key-press

event in the FIFO (if there is one) and the FIFO status,

so it is easy to operate the MAX7347/MAX7348/

MAX7349 by polling. If the INT pin is not required, it

can be configured as an open-drain general-purpose

output (GPO) capable of driving an LED.

Key-Scan Controller

Key inputs are scanned statically, not dynamically, to

ensure low-EMI operation. As inputs only toggle in

response to switch changes, the key matrix can be

routed closer to sensitive circuit nodes.

The key controller debounces and maintains a FIFO of

key-press events (including autorepeated key presses,

if autorepeat is enabled). Figure 1 shows keys order.

The MAX7349 monitors up to 64 keys. The MAX7348

monitors up to 40 keys. The MAX7347 monitors up to

24 keys (Table 1).

Serial Interface

Figure 2 shows the 2-wire serial interface timing details.

If the application requires fewer keys to be scanned, up

to six of the key-switch outputs can be configured as

open-drain GPOs capable of driving LEDs. For each

key-switch output used as a GPO, the number of key

switches that can be scanned is reduced by eight.

Serial Addressing

The MAX7347/MAX7348/MAX7349 operate as slaves

that send and receive data through an I²C-compatible

2-wire interface. The interface uses a serial data line

(SDA) and a serial clock line (SCL) to achieve bidirec-

tional communication between master(s) and slave(s).

A master (typically a microcontroller) initiates all data

transfers to and from the MAX7347/MAX7348/MAX7349

and generates the SCL clock that synchronizes the

data transfer.

8/MAX7349

An alert logic input (MAX7349 only) can be configured

to deliver an automatic, customizable sound and/or an

interrupt on every falling edge of the logic input. The

logic state of the alert input can be read at any time.

Tone Generator

The piezo sounder controller generates a square wave

with the frequency of a musical tone under processor con-

trol. The selection of tones covers the 5th musical octave

(523.25Hz to 987.77Hz), plus seven other notes up to

2637Hz. The sounder output is also programmable to be

either high or low for the entire sound duration to operate

an electronic sounder, relay, or lamp instead of a piezo

transducer. The sound duration is programmable from

15.625ms in seven binary steps up to a maximum of 1s.

The MAX7347/MAX7348/MAX7349s’ SDA line operates

as both an input and an open-drain output. A pullup

resistor, typically 4.7kΩ, is required on SDA. The

MAX7347/MAX7348/MAX7349s’ SCL line operates only

as an input. A pullup resistor, typically 4.7kΩ, is required

on SCL if there are multiple masters on the 2-wire inter-

face, or if the master in a single-master system has an

open-drain SCL output.

Each transmission consists of a START condition

(Figure 3) sent by a master, followed by the MAX7347/

MAX7348/MAX7349 7-bit slave address plus R/W bit, a

register address byte, 1 or more data bytes, and finally

a STOP condition.

The piezo sounder controller interface uses a single 1-

byte access to its own separate slave address.

Commands are double-buffered to allow two commands

(2 bytes) to be stored and executed in succession. The

sounder controller performs the transition between

queued sound commands without click artifacts. The

controller can also autoloop between the two most

recent commands. Autolooping allows a wide range of

intermittent and two-tone sounds to be initiated, and

then run automatically without further intervention.

Start and Stop Conditions

Both SCL and SDA remain high when the interface is

not busy. A master signals the beginning of a transmis-

sion with a START (S) condition by transitioning SDA

from high to low while SCL is high. When the master

has finished communicating with the slave, it issues a

6

_______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

*MAX7348 AND

MAX7349 ONLY.

**MAX7349 ONLY.

KEY

0

KEY

8

KEY

16

KEY

24

KEY

32

KEY

40

KEY

48

KEY

56

COL7/PORT7**

COL6/PORT6**

COL5/PORT5**

COL4/PORT4*

COL3/PORT3*

COL2/PORT2

COL1

KEY

1

KEY

9

KEY

17

KEY

25

KEY

33

KEY

41

KEY

49

KEY

57

KEY

2

KEY

10

KEY

18

KEY

26

KEY

34

KEY

42

KEY

50

KEY

58

COL0

ROW0

ROW1

ROW2

KEY

3

KEY

11

KEY

19

KEY

27

KEY

35

KEY

43

KEY

51

KEY

59

ROW3

ROW4

ROW5

ROW6

KEY

4

KEY

12

KEY

20

KEY

28

KEY

36

KEY

44

KEY

52

KEY

60

ROW7

KEY

5

KEY

13

KEY

21

KEY

29

KEY

37

KEY

45

KEY

53

KEY

61

KEY

6

KEY

14

KEY

22

KEY

30

KEY

38

KEY

46

KEY

54

KEY

62

KEY

7

KEY

15

KEY

23

KEY

31

KEY

39

KEY

47

KEY

55

KEY

63

Figure 1. Keys Order

STOP (P) condition by transitioning SDA from low to

high while SCL is high. The bus is then free for another

transmission.

byte of data. Thus, each byte transferred effectively

requires 9 bits. The master generates the 9th clock

pulse, and the recipient pulls down SDA during the

acknowledge clock pulse, so the SDA line is stable low

during the high period of the clock pulse. When the

master is transmitting to the MAX7347/MAX7348/

MAX7349, the MAX7347/MAX7348/MAX7349 generate

the acknowledge bit because the MAX7347/MAX7348/

MAX7349 are the recipients. When the MAX7347/

MAX7348/MAX7349 are transmitting to the master, the

master generates the acknowledge bit because the

master is the recipient.

Bit Transfer

One data bit is transferred during each clock pulse

(Figure 4). The data on SDA must remain stable while

SCL is high.

Acknowledge

The acknowledge bit is a clocked 9th bit (Figure 5),

which the recipient uses to handshake receipt of each

_______________________________________________________________________________________

7

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

SDA

t

BUF

t

SU, DAT

t

SU, STA

t

HD, STA

t

LOW

t

SU, STO

t

HD, DAT

t

HIGH

SCL

t

HD, STA

t

R

t

F

START

CONDITION

REPEATED

START CONDITION

STOP

CONDITION

START

CONDITION

Figure 2. 2-Wire Serial Interface Timing Details

SDA

8/MAX7349

SCL

P

S

STOP

CONDITION

START

CONDITION

Figure 3. Start and Stop Conditions

SDA

SCL

DATA LINE STABLE;

DATA VALID

CHANGE OF DATA

ALLOWED

Figure 4. Bit Transfer

8

_______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Table 2. Key-Switch Mapping

COL0

KEY 0

KEY 1

KEY 2

KEY 3

KEY 4

KEY 5

KEY 6

KEY 7

COL1

COL2/PORT2 COL3/PORT3 COL4/PORT4 COL5/PORT5 COL6/PORT6 COL7/PORT7

ROW0

ROW1

ROW2

ROW3

ROW4

ROW5

ROW6

ROW7

KEY 8

KEY 16

KEY 17

KEY 18

KEY 19

KEY 20

KEY 21

KEY 22

KEY 23

KEY 24

KEY 25

KEY 26

KEY 27

KEY 28

KEY 29

KEY 30

KEY 31

KEY 32

KEY 33

KEY 34

KEY 35

KEY 36

KEY 37

KEY 38

KEY 39

KEY 40

KEY 41

KEY 42

KEY 43

KEY 44

KEY 45

KEY 46

KEY 47

KEY 48

KEY 49

KEY 50

KEY 51

KEY 52

KEY 53

KEY 54

KEY 55

KEY 56

KEY 57

KEY 58

KEY 59

KEY 60

KEY 61

KEY 62

KEY 63

KEY 9

KEY 10

KEY 11

KEY 12

KEY 13

KEY 14

KEY 15

Table 3. 2-Wire Interface Address Map

DEVICE ADDRESS

PIN AD0

FUNCTION

A7

A6

A5

A4

A3

A2

A1

A0 R/W

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

Key-scan controller write

Key-scan controller read

Sounder controller write

Sounder controller read

Key-scan controller write

Key-scan controller read

Sounder controller write

Sounder controller read

Key-scan controller write

Key-scan controller read

Sounder controller write

Sounder controller read

Key-scan controller write

Key-scan controller read

Sounder controller write

Sounder controller read

0

GND

0

1

0

1

0

1

0

1

0

1

V+

0

1

0

1

0

1

SDA

SCL

controller. The AD0 input can be connected to any of

four signals: GND, V+, SDA, or SCL, giving four possible

slave address pairs, allowing up to four MAX7348/

MAX7349 devices to share the bus. Only one MAX7347

can share the bus. The MAX7347 AD0 input is internally

connected to GND.

Slave Addresses

The MAX7347/MAX7348/MAX7349 have two 7-bit long

slave addresses (Figure 6). The bit following a 7-bit

slave address is the R/W bit, which is low for a write

command and high for a read command.

The first 4 bits (MSBs) of the MAX7347/MAX7348/

MAX7349 slave addresses are always 0111. Slave

address bits A3, A2, and A1 correspond, by the matrix

in Table 3, to the states of the device address input

AD0, and A0 corresponds to the R/W bit. MAX7347/

MAX7348/MAX7349 use two slave addresses, one for

the main key-scan controller, and one for the sounder

The MAX7347/MAX7348/MAX7349 monitor the bus

continuously, waiting for a START condition followed by

its slave address. When MAX7347/MAX7348/MAX7349

recognize their slave address, they acknowledge and

are then ready for continued communication.

_______________________________________________________________________________________

9

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

START

CONDITION

CLOCK PULSE FOR

ACKNOWLEDGE

1

2

8

9

SCL

SDA

BY

TRANSMITTER

SDA

BY

RECEIVER

S

Figure 5. Acknowledge

0

1

A3

A2

A1

R/W

ACK

SDA

SCL

MSB

LSB

Figure 6. Slave Address

Any bytes received after the command byte are data

bytes. The first data byte goes into the internal register

of the MAX7347/MAX7348/MAX7349 selected by the

command byte (Figure 8).

Bus Timeout

The MAX7347/MAX7348/MAX7349 feature a 20ms mini-

mum bus timeout on the 2-wire serial interface, largely to

prevent the MAX7347/MAX7348/MAX7349 from holding

the SDA I/O low during a read transaction if the SCL

hangs for any reason before a serial transaction has

been completed. Bus timeout operates by causing the

MAX7347/MAX7348/MAX7349 to internally terminate a

serial transaction, either read or write, if the time between

adjacent edges on SCL exceeds 20ms. After a bus time-

out, the MAX7347/MAX7348/MAX7349 wait for a valid

START condition before responding to a consecutive

transmission. The bus timeout feature requires the serial

interface to operate above 50Hz bus speed. This feature

can be enabled or disabled under user control by writing

to the configuration register (Table 12).

If multiple data bytes are transmitted before a STOP

condition is detected, these bytes are generally stored

in subsequent MAX7347/MAX7348/MAX7349 internal

registers (Table 7) because the command byte address

generally autoincrements (Table 4).

8/MAX7349

Message Format for Reading the

Key-Scan Controller

The MAX7347/MAX7348/MAX7349 are read using the

MAX7347/MAX7348/MAX7349s’ internally stored com-

mand byte as an address pointer, the same way the

stored command byte is used as an address pointer for

a write. The pointer generally autoincrements after each

data byte is read using the same rules as for a write

(Table 4). Thus, a read is initiated by first configuring

the MAX7347/MAX7348/MAX7349s’ command byte by

performing a write (Figure 7). The master can now read

n consecutive bytes from the MAX7347/MAX7348/

MAX7349, with the first data byte being read from the

register addressed by the initialized command byte.

When performing read-after-write verification, remem-

ber to reset the command byte’s address because the

stored command byte address is generally autoincre-

mented after the write (Figure 9, Table 4).

Message Format for Writing the

Key-Scan Controller

A write to the MAX7347/MAX7348/MAX7349s’ key-scan

controller comprises the transmission of the

MAX7347/MAX7348/MAX7349s’ key-scan slave address

with the R/W bit set to zero, followed by at least 1 byte of

information. The first byte of information is the command

byte. The command byte determines which register of the

MAX7347/MAX7348/MAX7349 is to be written by the next

byte, if received. If a STOP condition is detected after the

command byte is received, then the MAX7347/MAX7348

/MAX7349 take no further action (Figure 7) beyond stor-

ing the command byte.

10 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

COMMAND BYTE IS STORED ON RECEIPT OF

D7 D6 D5 D4 D3 D2 D1 D0

ACKNOWLEDGE CONDITION

ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349

S

SLAVE ADDRESS

0

A

COMMAND BYTE

A

P

R/W

ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349

Figure 7. Command Byte Received

ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349

D7 D6 D5 D4 D3 D2 D1 D0

ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349

D7 D6 D5 D4 D3 D2 D1 D0

ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349

S

SLAVE ADDRESS

0

A

COMMAND BYTE

A

DATA BYTE

1 BYTE

A

P

R/W

AUTOINCREMENT

COMMAND BYTE ADDRESS

Figure 8. Command and Single Data Byte Received

Message Format for Writing the Sounder

Controller

Table 4. Key-Scan Command Address

Autoincrement Rules

A write to the MAX7347/MAX7348/MAX7349s’ sounder

controller comprises the transmission of the

MAX7347/MAX7348/MAX7349s’ sounder slave address

with the R/W bit set to zero, followed by at least 1 com-

mand byte of information. The sounder controller ana-

lyzes each incoming data byte, and depending on the

state of the sounder controller’s 2-deep FIFO and the

contents of the command byte, the command byte is

added to the FIFO or it overwrites the last FIFO data

item (Table 16).

REGISTER

FUNCTION

ADDRESS

CODE (hex)

AUTOINCREMENT

ADDRESS (hex)

Keys FIFO

0x00

0x01

0x02

0x03

0x04

0x05

0x06

0x07

0x00

0x02

0x03

0x04

0x05

0x06

0x07

0x00

Debounce

Autorepeat

Interrupt

Configuration

Port

Message Format for Reading the Sounder

Controller

Key Sound

Alert Sound

A read from the MAX7347/MAX7348/MAX7349s’ sounder

controller comprises the transmission of the

MAX7347/MAX7348/MAX7349s’ sounder slave address

with the R/W bit set to 1. The master can now read n con-

secutive bytes from the MAX7347/MAX7348/MAX7349,

each byte being a snapshot of the FIFO status of the

sounder controller (Table 16). If the master wishes to poll

the sounder controller until there is room for another com-

mand to be sent, the master can read bytes continuously

from the sounder controller until the information is satis-

factory and then issue a STOP condition.

Operation with Multiple Masters

If the MAX7347/MAX7348/MAX7349 are operated on a 2-

wire interface with multiple masters, a master reading the

MAX7347/MAX7348/MAX7349 should use a repeated

start between the write that sets the MAX7347/MAX7348/

MAX7349s’ address pointer, and the read(s) that takes

the data from the location(s). This is because it is possi-

ble for master 2 to take over the bus after master 1 has

set up the MAX7347/MAX7348/MAX7349s’ address

pointer but before master 1 has read the data. If master 2

subsequently resets the MAX7347/MAX7348/MAX7349s’

address pointer, then master 1’s read may be from an

unexpected location.

______________________________________________________________________________________ 11

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Table 5. Key-Scan Power-Up Configuration

REGISTER DATA

REGISTER

FUNCTION

ADDRESS

CODE (hex)

POWER-UP CONDITION

D7 D6 D5 D4 D3 D2 D1 D0

Keys FIFO

Debounce

Autorepeat

Interrupt

Empty

0x00

0x01

0x02

0x03

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

Ports 2–7 are enabled; debounce time is 39ms

Autorepeat is disabled

INT is a port, not an interrupt output

Shutdown mode: key sound is disabled; alert sound is

disabled; alert INT is disabled; timeout enabled; no

sound output

Configuration

0x04

0

1

Ports

Ports 2–7 and INT are logic-high (high impedance)

Key-sound default is 31.25ms of 987.77Hz

Key-sound default is 250ms of 2093Hz

0x05

0x06

0x07

1

0

1

0

1

0

1

0

1

0

1

0

1

X

1

Key Sound

Alert Sound

X = Don’t care.

Table 6. Sounder Power-Up Configuration

REGISTER DATA

POWER-UP CONDITION

D7

D6

D5

D4

D3

D2

D1

D0

Sounder output is a general-purpose output, logic 0; queue is empty

0

8/MAX7349

ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349

D7 D6 D5 D4 D3 D2 D1 D0

ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349

D7 D6 D5 D4 D3 D2 D1 D0

ACKNOWLEDGE FROM MAX7347/MAX7348/MAX7349

SLAVE ADDRESS

S

0

A

COMMAND BYTE

A

DATA BYTE

N BYTES

A

P

R/W

AUTOINCREMENT

COMMAND BYTE ADDRESS

Figure 9. N Data Bytes Received

12 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Table 7. Key-Scan Register Address Map

ADDRESS

CODE

COMMAND ADDRESS

REGISTER

FUNCTION

(hex)

D15

0

D14

0

D13

0

D12

0

D11

0

D10

0

D9

0

D8

0

Keys FIFO

0x00

0x01

0x02

0x03

0x04

0x05

0x06

0x07

Debounce

Autorepeat

Interrupt

0

1

0

1

0

1

Configuration

Ports

0

1

0

1

0

1

Key Sound

Alert Sound

0

1

0

1

Table 8. Keys FIFO Register Format

ADDRESS

CODE

(hex)

REGISTER DATA

D5 D4 D3

REGISTER

D7

D6

D2

D1

D0

OVERFLOW

FLAG

MORE

FLAG

KEY SWITCH THAT HAS BEEN

DEBOUNCED

KEYS FIFO REGISTER*

0X00

FIFO has not overflowed

0x00

0

1

X

FIFO overflowed; FIFO contains the first eight

key events

This key is the last FIFO item (key-switch data

not zero)

0x00

X

0

X

0

X

0

X

0

X

0

X

0

X

0

Key 0 was EITHER the last FIFO item OR the

FIFO is empty and no key has been pressed

This key is not the last FIFO item

0x00

X

1

X

Power-up default setting

0

*Reading the key-scan FIFO clears the INT. INT is only reasserted by a key event after the FIFO has been emptied by read(s).

Command Address Autoincrementing

Registers Description

Address autoincrementing allows the MAX7347/

MAX7348/MAX7349 to be configured with fewer trans-

missions by minimizing the number of times the com-

mand address needs to be sent. The command

address stored in the MAX7347/MAX7348/MAX7349

generally increments after each data byte is written or

read (Table 4). Autoincrementing applies only to the

key-scan command addresses and not to the sounder

command addresses.

Initial Power-Up

On power-up, all control registers are reset and the

MAX7347/MAX7348/MAX7349 enter shutdown mode

(Tables 5, 6). Table 7 shows the register address map

for the key-scan section.

______________________________________________________________________________________ 13

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Table 9. Debounce Register Format

ADDRESS CODE

REGISTER

REGISTER DATA

(hex)

D7

D6

D5

D4

D3

D2

D1

D0

DEBOUNCE REGISTER

0x01

PORTS ENABLE

DEBOUNCE TIME

Debounce time is 9ms

0x01

X

0

1

Debounce time is 10ms

Debounce time is 11ms

Debounce time is 12ms

All the way through to

Debounce time is 37ms

Debounce time is 38ms

Debounce time is 39ms

Debounce time is 40ms

0

1

0

1

—

1

—

1

—

1

—

0

—

0

1

0

1

0

1

GPO ports disabled (full key-scan functionality)

GPO port 7 enabled

0x01

0

1

0

1

0

1

0

1

0

1

0

1

X

1

X

1

X

1

X

1

X

1

X

1

GPO ports 7 and 6 enabled

GPO ports 7, 6, and 5 enabled

GPO ports 7, 6, 5, and 4 enabled

GPO ports 7, 6, 5, 4, and 3 enabled

GPO ports 7, 6, 5, 4, 3, and 2 enabled

Power-up default setting

8/MAX7349

Debounce Register

Key-Scan Registers

The debounce register sets the time for each debounce

cycle, as well as setting whether the GPO ports are

enabled or disabled. Bits D0 through D4 set the

debounce time in increments of 1ms starting at 9ms

and ending at 40ms (Table 9). Bits D5 through D7 set

which one of the GPO ports is to be enabled. Note that

not any port can be enabled at a particular time. The

GPO ports can be enabled only in the combinations

shown in Table 9, from all disabled to all enabled.

Eight key-scan registers are described in the following

sections.

Keys FIFO Register

The keys FIFO register contains the information pertain-

ing to the status of the keys FIFO, as well as the key-

press events that have been debounced (Table 8). Bits

D0 to D5 denote which of the 64 keys have been

debounced and the keys are numbered as in Table 2

and Figure 1. D6 indicates whether the present

debounced key is the last one in the FIFO, with 1

denoting that there are more keys after the present one,

and 0 denoting that the present debounced key is the

last one stored in the FIFO. D7 is the overflow flag,

which denotes whether the keys FIFO has overflowed.

Autorepeat Register

The autorepeat register sets the autorepeat frequency

(repeat rate) and its delay. The autorepeat function allows

a key to be consecutively asserted when the key itself is

pressed down without being released. The autorepeat

delay specifies the delay between the first press and the

beginning of the autorepeating, provided that the key has

not been released. The autorepeat frequency specifies

how fast the continuously pressed-down key to be assert-

ed once autorepeating has started is. Bits D0 through D3

specify the autorepeat delay in terms of debounce cycles

Reading the key-scan FIFO clears the interrupt INT. INT

is only reasserted after the FIFO has been emptied by

performing enough read operations.

14 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

ranging from 8 debounce cycles to 128 debounce cycles

sounder output has been enabled to be set by a key

debounce event in the configuration register. When this

happens, the information of bits D7 through D1 is passed

on to the sounder register and the appropriate sound is

executed (Tables 14, 16). Least significant bit D0 is

ignored and always set to 1 when transferred to the

sounder register. See Table 16 for the format of setting

the frequency and duration of the sound to be executed.

If a key-sound register command is sent as 000xxxx

(continuous), then the command is stored as 111xxxx

(1000ms) in the sounder register.

(Table 10). Bits D4 through D6 specify the autorepeat

rate or frequency ranging from 4 to 32 debounce cycles.

Bit D7 specifies whether the auto-repeat function is

enabled with 0 denoting autorepeat disabled and 1

denoting autorepeat enabled.

Interrupt Register

The interrupt register contains information related to the

settings of the interrupt request function, as well as the

status of the INT output, which can also be configured

as a GPO. Bits D0 through D4 set the key-scan interrupt

frequency. By setting bits D0 through D4 to an appropri-

ate value, the interrupt can be asserted at the end of the

selected number of debounce cycles (Table 11). This

number ranges from 1 to 31 debounce cycles. If bits D0

through D4 are set to 00000, the INT output is config-

ured as a GPO that is controlled by bit D6 in the ports

register and the INT output is not asserted. However, the

INT status bits D5, D6, and D7 are still set and cleared in

the normal way at the end of each debounce cycle as if

bits D0 through D4 were set to 00001.

Alert Sound Register

The alert sound register specifies the duration and fre-

quency of the sound to be executed by the sounder con-

troller at the falling edge of the alert input if the sounder

output has been enabled to be set by the alert input in

the configuration register. If this is the case, the informa-

tion of bits D7 through D1 is passed on to the sounder

register and the appropriate sound is executed (Tables

15, 16). Least significant bit D0 is always set to 1 and

this value is ignored when transferred to the sounder

register. See Table 16 for the proper format of setting the

frequency and duration of the sound to be executed.

Note that if an alert sound register command is sent as

000xxxx (continuous), then the command is actually

stored as 111xxxx (1000ms) in the sounder register.

Bits D5 and D6 denote whether an interrupt was set

due to a key-scan event (bit D5) or to an alert event (bit

D6). Bit D7 represents whether an interrupt request has

been asserted with 0 denoting no INT asserted and 1

denoting that INT has been asserted.

The interrupt register is a read-only register and writes

to it are ignored. Reading the interrupt register does

clear an alert event INT, but does not clear a key-scan

event INT. An interrupt request caused by a key-scan

event(s) is cleared when the FIFO is emptied.

Sounder Register

The sounder register stores the frequencies and duration

of the sounds to be executed by the sounder, as well as

the state of its two-deep FIFO (Table 16). D0 denotes

whether another command is lined in the queue at any

given moment. A 0 in D0 denotes that the queue is empty

while a 1 denotes that there is another command. By writ-

ing 0 to D0, the present command is executed and the

queue is cleared. When sending a command that has a

D0 set to 1, the queue is checked and, if empty, the sent

command is added to it while, if full, the sent command

replaces the queued command.

Configuration Register

The configuration register reflects the sounder status,

controls the I²C bus timeout feature, enables the alert

input interrupt feature, enables the sounder to respond

to both alert input and key debounce events, and con-

trols the shutdown of the device (Table 12).

Bits D0 and D1, when taken in conjunction, set the level

of the sounder output when configured as a GPO and

also control the autoloop function provided that the rest of

the bits (D7 through D2) are set to 0. When the sounder is

configured as a GPO, the levels of the output are set by

D1, a 0 denoting a low and a 1 denoting a high. When D0

is set to 1 and the rest of the bits are set to 0, D1 controls

the autoloop function as defined in Table 16.

Ports Register

The ports register sets the values of ports 2 through 7 and

the INT port when configured as GPOs. The settings in

this register are ignored for ports not configured as

GPOs, and a read from this register returns the values

stored in the register and not the actual port conditions

(Table 13). The ports register also serves to read the alert

input and this is done through bit D0 with a 0 denoting a

low on the alert input and a 1 denoting a high.

Bits D7 through D1 control the frequency and duration of

the sounds to be executed by the sounder. These sounds

include the musical notes of the 5th octave plus some

notes from the 6th and 7th octaves as well. See Table 16.

Key-Sound Register

The key-sound register specifies the duration and fre-

quency of the sound to be executed by the sounder con-

troller when a key or a set of keys are debounced if the

______________________________________________________________________________________ 15

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Table 10. Autorepeat Register Format

ADDRESS

CODE

(hex)

REGISTER DATA

REGISTER

D7

D6

D5

D4

D3

D2

D1

D0

AUTOREPEAT

RATE

AUTOREPEAT REGISTER

0x02

ENABLE

AUTOREPEAT DELAY

Autorepeat is disabled

0x02

0

1

X

AUTOREPEAT

RATE

Autorepeat is enabled

AUTOREPEAT DELAY

Key-switch autorepeat delay is 8 debounce cycles

Key-switch autorepeat delay is 16 debounce cycles

Key-switch autorepeat delay is 24 debounce cycles

Key-switch autorepeat delay is 32 debounce cycles

Key-switch autorepeat delay is 40 debounce cycles

Key-switch autorepeat delay is 48 debounce cycles

Key-switch autorepeat delay is 56 debounce cycles

Key-switch autorepeat delay is 64 debounce cycles

Key-switch autorepeat delay is 72 debounce cycles

Key-switch autorepeat delay is 80 debounce cycles

Key-switch autorepeat delay is 88 debounce cycles

Key-switch autorepeat delay is 96 debounce cycles

Key-switch autorepeat delay is 104 debounce cycles

Key-switch autorepeat delay is 112 debounce cycles

Key-switch autorepeat delay is 120 debounce cycles

Key-switch autorepeat delay is 128 debounce cycles

0x02

1

X

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

X

8/MAX7349

Key-switch autorepeat frequency is 4 debounce cycles

Key-switch autorepeat frequency is 8 debounce cycles

Key-switch autorepeat frequency is 12 debounce cycles

Key-switch autorepeat frequency is 16 debounce cycles

Key-switch autorepeat frequency is 20 debounce cycles

Key-switch autorepeat frequency is 24 debounce cycles

Key-switch autorepeat frequency is 28 debounce cycles

Key switch autorepeat frequency is 32 debounce cycles

Power-up default setting

0x02

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

X

0

X

0

X

0

X

0

16 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Table 11. Interrupt Register Format

REGISTER DATA

ADDRESS

CODE (hex)

REGISTER

D7

D6

D5

D4

D3

D2

D1

D0

KEY-

SCAN

EVENT*

INT

STATUS*

ALERT

EVENT*

KEY-SCAN INTERRUPT

FREQUENCY

INTERRUPT REGISTER

0x03

Current INT is due to key-scan event(s)

Current INT is due to alert event

0x03

1

0

1

0

X

Current INT is due to both key-scan event(s)

and alert event

0x03

1

0

1

0

1

0

X

INT has not been asserted

INT has been asserted

KEY-

SCAN

EVENT

ALERT

EVENT

0x03

1

X

INT output pin is NOT asserted; INT output

pin is used as a general-purpose output

called INT port under control of bit D6 in

ports register; INT status bits D5, D6, D7 are

still set and cleared in the normal way at the

end of every debounce cycle as if bits D4–D0

were set to 00001

X

0

1

Key-scan INT is asserted at the end of every

debounce cycle, if new key(s) is debounced

0x03

Key-scan INT is asserted at the end of every

2 debounce cycles, if new key(s) is

debounced

X

—

X

—

X

—

X

0

—

1

0

—

1

0

—

1

—

0

—

1

-—

Key-scan INT is asserted at the end of every

29 debounce cycles, if new key(s) is

debounced

0x03

Key-scan INT is asserted at the end of every

30 debounce cycles, if new key(s) is

debounced

X

1

0

Key-scan INT is asserted at the end of every

31 debounce cycles, if new key(s) is

debounced

0x03

X

1

Power-up default setting

0

*Read-only register bits; write data is ignored. Reading the interrupt register does clear an alert event INT, but does not clear a key-

scan event INT. INT caused by key-scan event(s) is cleared when FIFO is emptied.

______________________________________________________________________________________ 17

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Table 12. Configuration Register Format

REGISTER DATA

D5 D4

ALERT ALERT ALERT

ADDRESS

CODE (hex)

REGISTER

D7

D6

D3

D2

D1

D0

KEY

SOUNDER TIMEOUT

STATUS ENABLE

CONFIGURATION REGISTER

0x04

SHUTDOWN SOUND SOUND

INT

ENABLE ENABLE ENABLE EVENT

Serial interface bus timeout enabled

Serial interface bus timeout disabled

No active sounder output

0x04

X

0

X

0

1

X

Active sounder output set by serial

interface

0x04

X

0

1

0

1

X

Active sounder output set by key

debounce event

Active sounder output set by an alert

event

Alert input interrupt (if enabled) is

asserted according to key-scan

interrupt rules

0x04

X

0

1

X

Alert input interrupt (if enabled) is

asserted immediately

8/MAX7349

Alert input does not cause an

interrupt

0x04

X

0

1

X

Falling edge of alert input causes

interrupt

Alert input does not cause an

automatic sound

0x04

X

0

1

X

Falling edge of alert input causes the

8-bit contents of the alert sound

register 0x07 to be sent to the

sounder

Debounce key(s) do not cause an

automatic sound

0x04

X

0

1

X

Debounced key(s), including

autorepeated keys, cause the 8-bit

contents of the key-sound register

0x06 to be sent to the sounder

18 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Table 12. Configuration Register Format (continued)

REGISTER DATA

D5 D4

ALERT ALERT ALERT

ADDRESS

CODE (hex)

REGISTER

D7

D6

D3

D2

D1

D0

KEY

SOUNDER TIMEOUT

STATUS ENABLE

CONFIGURATION REGISTER

0x04

SHUTDOWN SOUND SOUND

INT

ENABLE ENABLE ENABLE EVENT

Shutdown mode; key-scan and

sounder timing are disabled,

interrupts disabled, but alert input

can be read and port outputs (as

selected) can be changed

0x04

0

X

Operating mode; key scan is started,

and commands in sounder queue

are actioned

0x04

1

X

Power-up default setting

0

1

Table 13. Ports Register Format

REGISTER DATA

ADDRESS

CODE (hex) WRITE

READ

REGISTER

D7

D6

D5

D4

D3

D2

D1

D0

INT

PORT

ALERT

INPUT

READ

0x05

PORT 7 PORT 6 PORT 5 PORT 4 PORT 3 PORT 2

PORTS REGISTER

INT

PORT

WRITE PORT 7 PORT 6 PORT 5 PORT 4 PORT 3 PORT 2

X

Clear port 2 low

0x05

Write

X

0

1

X

0

1

X

0

1

X

0

1

X

0

1

X

Set port 2 high (high

impedance)

Clear port 3 low

Set port 3 high (high

impedance)

Clear port 4 low

Set port 4 high (high

impedance)

Clear port 5 low

Set port 5 high (high

impedance)

Clear port 6 low

Set port 6 high (high

impedance)

______________________________________________________________________________________ 19

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Table 13. Ports Register Format (continued)

REGISTER DATA

D4 D3

ADDRESS

CODE (hex) WRITE

READ

REGISTER

D7

D6

D5

D2

D1

D0

INT

PORT

ALERT

INPUT

READ

0x05

PORT 7 PORT 6 PORT 5 PORT 4 PORT 3 PORT 2

PORTS REGISTER

INT

PORT

WRITE PORT 7 PORT 6 PORT 5 PORT 4 PORT 3 PORT 2

X

Clear port 7 low

0x05

Write

0

1

X

Set port 7 high (high

impedance)

X

Clear INT port low;

this setting is ignored

unless the key-scan INT

functionality is disabled

by setting interrupt

register bits D4 to D0 to

00000

Set INT port high (high

impedance); this setting

is ignored unless the

key-scan INT

0x05

Write

X

0

1

X

functionality is disabled

by setting interrupt

register bits D4 to D0 to

00000

8/MAX7349

Alert input level is low

Alert input level is high

0x05

Read

X

0

1

Power-up default

setting

0x05

—

1

X

Table 14. Key-Sound Register Format

REGISTER DATA

ADDRESS

CODE (hex)

REGISTER

D7

D6

D5

D4

D3

D2

D1

D0

1

This-8 bit value is passed to sounder controller when key(s)

debounced, if enabled in the configuration register; these 7

bits define duration and frequency only; sounder command

bit D0 is ignored and fixed internally at 1; if a key sound is

sent as 000xxxxx (continuous), then the command is stored

as 111xxxxx (1000 ms)

0x06

7-bit value (see Table 16 for functionality)

Power-up default setting

0

1

0

1

0

1

20 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Table 15. Alert Sound Register Format

REGISTER DATA

D5 D4 D3 D2

ADDRESS

CODE (hex)

REGISTER

D7

D6

D1

D0

1

This 8-bit value is passed to sounder controller on the falling

edge of the alert input; these 7 bits define duration and

frequency only; sounder command bit D0 is ignored and

fixed internally at 1; if an alert sound is sent as 000xxxxx

(continuous), then the command is stored as 111xxxxx

(1000 ms)

0x07

7-bit value (see Table 16 for functionality)

Power-up default setting

1

0

1

0

1

Table 16. Sounder Register Format

REGISTER DATA

D4 D3 D2

FREQUENCY LEVEL BUFFER

REGISTER

READ

WRITE

D7 D6 D5

DURATION

D1

D0

SOUNDER REGISTER

No commands are active; OR output is GPO logic 0

Read

0

This current command is active, none are queued (so another

command may be sent)

DURATION

FREQUENCY LEVEL

This current command is active, and another command is in

the queue

Read

1

Perform this command, terminating and clearing any previous

active command, command queue, and autoloop; new

command is now active, and queue is now empty

Write

X

0

1

Add command to queue if not full; command replaces queued

command if queue is full

X

Configure sounder output as general-purpose output, logic 0

(clear queue; sounder output active low with continuous

duration, ie, until a buffer = 0 command)

Write

0

1

0

Configure sounder output as general-purpose output, logic 1

(clear queue; sounder output active high with continuous

duration, ie, until a buffer = 0 command)

Autoloop using the current two commands; the active

command is command 1, and the inactive command is

command 2; if no command is active, the oldest command is

reactivated as command 1, and the other command is re-

activated as command 2

Write

0

1

Autoloop is halted at the end of command 2, and output idles

as defined by command 2

______________________________________________________________________________________ 21

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Table 16. Sounder Register Format (continued)

REGISTER DATA

D4 D3 D2

FREQUENCY LEVEL BUFFER

REGISTER

READ

WRITE

D7 D6 D5

DURATION

D1

D0

SOUNDER REGISTER

Sounder output active low for sound duration;

queue cleared

—

Write

0

1

0

Sounder output active high for sound duration;

queue cleared

Sound frequency is 523.25Hz, idles low

Sound frequency is 587.33Hz, idles low

Sound frequency is 659.26, idles low

Sound frequency is 698.46Hz, idles low

Sound frequency is 783.99Hz, idles low

Sound frequency is 880Hz, idles low

Sound frequency is 987.77Hz, idles low

Sound frequency is 1046.5Hz, idles low

Sound frequency is 1318.5Hz, idles low

Sound frequency is 1568Hz, idles low

Sound frequency is 1760Hz, idles low

Note C5

Note D5

Note E5

Note F5

Note G5

Note A5

Note B5

Note C6

Note E6

Note G6

Note A6

Write

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

DURATION

BUFFER

Sound frequency is 2093Hz, idles low

Sound frequency is 2349.3Hz, idles low

Sound frequency is 2637Hz, idles low

Note C7

Note D7

Note E7

Write

1

0

1

0

1

8/MAX7349

Sound duration is continuous; if an alert sound or

a key sound is programmed as 000xxxxx

(continuous), then the command is treated as

111xxxxx (1000 ms)

Write

0

Sound duration is 15625ms*

Sound duration is 3125ms*

Sound duration is 625ms*

Sound duration is 125ms*

Sound duration is 250ms*

Sound duration is 500ms*

Sound duration is 1000ms*

Power-up default setting

Write

—

0

1

0

1

0

1

0

1

0

1

0

1

0

1

0

FREQUENCY LEVEL BUFFER

0

*Sound duration will be slightly longer than these times because each sound always completes a full cycle before stopping.

22 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Sounder Operation

When an alert sound or key sound is happening, the user

Applications Information

Ghost-Key Elimination

Ghost keys are a phenomenon inherent with key-switch

matrices. When three switches located at the corners of

a matrix rectangle are pressed simultaneously, the

switch that is located at the last corner of the rectangle

(the ghost key) also appears to be pressed. This occurs

because the potentials at the two sides of the ghost-key

switch are identical due to the other three connections—

the switch is electrically shorted by the combination of

the other three switches (Figure 10). Because the key

appears to be pressed electrically, it is impossible for

software to detect which of the four keys is the ghost key.

cannot write to the sounder. The MAX7347/MAX7348/

MAX7349 do not acknowledge a write to the sounder I²C

address. However, a read from the sounder will work cor-

rectly. An alert sound or key sound event terminates a

current user-programmed event and clears the queue. If

an alert sound or key sound event is currently being

processed, then a new alert sound or key sound event

will be put into the queue, replacing an existing queued

alert sound or key sound event, if one exists. User access

to the sounder is restored when the last alert sound or key

sound event is completed. Note this means that the buffer

bit (D0) for an alert sound or key sound command is

effectively ignored.

The MAX7347/MAX7348/MAX7349 employ a proprietary

scheme that detects any three-key combination that

generates a fourth ghost key, and does not report any of

these four keys as being pressed. This means that

although ghost keys are never reported, many combina-

tions of three keys are effectively ignored when pressed

at the same time. Applications requiring three key com-

binations (such as <Ctrl><Alt><Del>) must ensure that

the 3 keys are not wired in positions that define the ver-

tices of a rectangle (Figure 11).

Shutdown

The MAX7347/MAX7348/MAX7349 are put into shut-

down mode by clearing bit D7 in the configuration reg-

ister (Table 12). In shutdown, the key-scan controller

and sounder controller are both disabled, and the

MAX7347/MAX7348/MAX7349 draw minimal current.

No additional supply current is drawn if any keys are

pressed. All switch matrix current sources are turned

off, and row outputs ROW0 to ROW7 and column out-

puts COL0 to COL7 become high impedance.

Low-EMI Operation

The MAX7347/MAX7348/MAX7349 use two techniques

to minimize EMI radiating from the key-switch wiring.

First, the voltage across the switch matrix never

exceeds 0.65V, irrespective of supply voltage V+. This

reduces the voltage swing at any node when a switch

is pressed to 0.65V maximum. Second, the keys are not

dynamically scanned, which would cause the key-

switch wiring to continuously radiate interference.

Instead, the keys are monitored for current draw (only

occurs when pressed), and debounce circuitry only

operates when one or more keys are actually pressed.

The alert input status may still be read in shutdown,

and an alert event can still cause an interrupt request if

this feature is enabled (Table 12). This means that alert

can be used for µC wakeup while the system sleeps

drawing minimum current.

Outputs configured as GPOs (COL2/PORT2 to

COL2/PORT7 and INT) may still be controlled in shut-

down and their output states can be changed under

software control at any time.

The sounder output may not be changed in shutdown,

even if it is effectively being used as a logic output. Writes

to the sounder during shutdown are ignored, and the

sounder FIFO is cleared on entering shutdown. However,

the sounder retains its output logic state for the duration

of shutdown, and so can be set low or high as desired by

writing 0x00 or 0x02, respectively, to the sounder register

(Table 12) before entering shutdown.

Power-Supply Considerations

The MAX7347/MAX7348/MAX7349 operate with a 2.4V

to 3.6V power-supply voltage. Bypass the power supply

to GND with a 0.047µF or higher ceramic capacitor as

close to the device as possible.

Switch On-Resistance

The MAX7347/MAX7348/MAX7349 are designed to be

insensitive to resistance either in the key switches or

the switch routing to and from the appropriate COLx

and ROWx up to 1kΩ. These controllers are therefore

compatible with low-cost membrane and conductive

carbon switches.

The MAX7347/MAX7348/MAX7349 may be taken out of

shutdown mode and put into operating mode by setting

bit D7 in the configuration register (Table 12). The key-

scan and sounder controller FIFOs are cleared, and key

monitoring starts. Note that rewriting the configuration

register with bit D7 high when bit D7 was already high

does not clear the FIFOs; the FIFOs are only cleared

when the MAX7347/MAX7348/MAX7349 are actually

coming out of shutdown.

______________________________________________________________________________________ 23

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

REGULAR KEY-PRESS

EXAMPLES OF VALID THREE-KEY COMBINATIONS

EVENT

GHOST-KEY

EVENT

KEY-SWITCH MATRIX

Figure 10. Ghost-Key Phenomenon

Figure 11. Valid Three-Key Combinations

V

CC

50kΩ

BIAS

OUT-

OUT+

SHDN

SHUTDOWN

10kΩ

16Ω

IN+

IN-

10kΩ

0.22μF

2.61kΩ

21.5kΩ

32.4kΩ

SOUNDER

OUTPUT

8/MAX7349

MAX4366

22nF

68nF

220pF

21.5kΩ

Figure 12. Third-Order Chebyshev Lowpass Filter and Output Stage

The sounder output can also drive a power amplifier for

higher sound levels. In this case, it is usually desirable

to include a lowpass filter before the speaker to convert

the square-wave tones to something closer to a sinu-

soid. The recommended cutoff frequency of this filter is

around 3kHz. An example circuit is shown in Figure 12,

which uses the uncommitted op amp of the MAX4366

bridge power amplifier to implement a third-order

Chebyshev lowpass filter.

Audio Transducers

The sounder output is designed to drive a standard, low-

cost piezo transducer directly without further buffering.

Piezo transducers appear as a capacitive load of typical-

ly 10nF. If a resistive or inductive sounder is used, such

as a small loudspeaker, fit a coupling capacitor between

the sounder output and the transducer. For example, if a

32Ω speaker is used, connect the positive side of a 22µF

electrolytic capacitor to the sounder output, the negative

side of the capacitor to one end of the speaker, and the

other end of the speaker to GND.

Chip Information

PROCESS: BiCMOS

24 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Typical Application Circuit

KEY 0

KEY 8

KEY 9

KEY 16

KEY 17

3.3V

COL2/PORT2

COL1

KEY 1

V+

MAX7348

COL0

KEY 2

KEY 3

KEY 10

KEY 11

KEY 18

KEY 19

COL3/PORT3

COL4/PORT4

AD0

ROW0

ROW1

ROW2

ROW3

ROW4

ROW5

ROW6

ROW7

5V

V+

KEY 4

KEY 5

KEY 12

KEY 13

KEY 20

KEY 21

SCL

SDA

SCL

SDA

INT

SOUNDER

KEY 6

KEY 7

KEY 14

KEY 15

KEY 22

KEY 23

GND

PIEZOELECTRIC

TRANSDUCER

______________________________________________________________________________________ 25

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Pin Configurations

TOP VIEW

+

ROW0

1

2

3

4

5

6

7

8

16 V+

ROW1

ROW2

ROW3

ROW4

ROW5

ROW6

ROW7

15 INT

TOP VIEW

+

14 SCL

13 SDA

12 GND

11 COL0

10 COL1

COL7/PORT7

1

2

3

4

5

6

7

8

9

24 ALERT

23 V+

MAX7347

ROW0

ROW1

22 INT

ROW2

21 SCL

MAX7349

ROW3

20 SDA

9

COL2/PORT2

COL3/PORT3

COL4/PORT4

ROW4

19 AD0

18 GND

QSOP

17 SOUNDER

16 COL0

15 COL1

14 COL2/PORT2

13 COL5/PORT5

ROW5

TOP VIEW

ROW6 10

ROW7 11

12

11

10

9

COL6/PORT6 12

COL1

8

7

6

5

INT 13

V+ 14

QSOP

COL2/PORT2

ROW7

MAX7347

ROW0

15

16

8/MAX7349

EP*

ROW6

ROW1

+

TOP VIEW

1

2

3

4

18 17 16 15 14 13

*EP = EXPOSED PADDLE

TOP VIEW

TQFN-EP

19

12

INT

COL1

V+ 20

11 COL2/PORT2

21

22

23

24

10

9

ALERT

COL5/PORT5

COL6/PORT6

+

MAX7349

COL7/PORT7

ROW0

ROW1

1

20 V+

ROW0

ROW1

ROW7

ROW6

8

2

3

4

5

6

7

8

9

19 INT

18 SCL

17 SDA

16 AD0

15 GND

EP*

7

+

ROW2

1

2

3

4

5

6

ROW3

MAX7348

COL3/PORT3

COL4/PORT4

ROW4

14

SOUNDER

TQFN-EP

ROW5

13 COL0

*EP = EXPOSED PADDLE

ROW6

12 COL1

ROW7 10

11 COL2/PORT2

QSOP

26 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH

1

21-0055

F

1

______________________________________________________________________________________ 27

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

8/MAX7349

PACKAGE OUTLINE,

12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm

1

E

21-0139

2

28 ______________________________________________________________________________________

2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

8/MAX7349

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

PACKAGE OUTLINE,

12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm

2

E

21-0139

2

Revision History

Pages changed at Rev 5: 1, 2, 23, 29

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 29

is a registered trademark of Maxim Integrated Products, Inc.


型号：	MAX7349AWG
厂家：	MAXIM INTEGRATED PRODUCTS
描述：	Microprocessor Circuit, BICMOS, PDSO24, 0.300 INCH, MS-013AD, SOIC-24 开关控制器
文件：	总29页 (文件大小：348K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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