2-Wire Interfaced Low-EMI Key Switch

and Sounder Controllers

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13

Command Address Autoincrementing

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.

Registers Description

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.

COMMAND ADDRESS

REGISTER

FUNCTION

D15

D14

D13

D12

D11

D10

D9

D8

ADDRESS

CODE

(hex)

Keys FIFO

0000

00

00

0x00

Debounce

0000

00

01

0x01

Autorepeat

0000

00

10

0x02

Interrupt

0000

00

11

0x03

Configuration

0000

01

00

0x04

Ports

0000

01

01

0x05

Key Sound

0000

01

10

0x06

Alert Sound

0000

01

11

0x07

Table 7. Key-Scan Register Address Map

REGISTER DATA

REGISTER

ADDRESS

CODE

(hex)

D7

D6

D5

D4

D3

D2

D1

D0

KEYS FIFO REGISTER*

0X00

OVERFLOW

FLAG

MORE

FLAG

KEY SWITCH THAT HAS BEEN

DEBOUNCED

FIFO has not overflowed

0x00

0

X

X

X

X

X

X

X

FIFO overflowed; FIFO contains the first eight

key events

0x00

1

X

X

X

X

X

X

X

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

not zero)

0x00

X

0

X

X

X

X

X

X

Key 0 was EITHER the last FIFO item OR the

FIFO is empty and no key has been pressed

0x00

0

0

0

0

0

0

0

0

This key is not the last FIFO item

0x00

X

1

X

X

X

X

X

X

Power-up default setting

0x00

0

0

0

0

00

00

Table 8. Keys FIFO Register Format

*

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).