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MAX7312

2-Wire-Interfaced 16-Bit I/O Port Expander with Interrupt and Hot-Insertion Protection

Maxim Integrated 

2-Wire-Interfaced 16-Bit I/O Port Expander

with Interrupt and Hot-Insertion Protection

MAX7312 generates the acknowledge bit since the

MAX7312 is the recipient. When the MAX7312 is trans-

mitting to the master, the master generates the

acknowledge bit.

Slave Address

The MAX7312 has a 7-bit-long slave address (Figure 6).

The 8th bit following the 7-bit slave address is the R/W

bit. Set this bit low for a write command and high for a

read command.

SDA A6 A5

MSB

PROGRAMMABLE

A4 A3 A2

A1 A0 R/W ACK

LSB

SDA

Slave address pins AD2, AD1, and AD0 choose 1 of 64

slave ID addresses (Table 7).

Data Bus Transaction

The command byte is the first byte to follow the 8-bit

device slave address during a write transmission

(Table 1, Figure 7). The command byte is used to deter-

mine which of the following registers are written or read.

Writing to Port Registers

Transmit data to the MAX7312 by sending the device

slave address and setting the LSB to a logic zero. The

command byte is sent after the address and deter-

mines which registers receive the data following the

command byte (Figure 7).

Figure 6. Slave Address

Table 1. Command Byte Register

COMMAND BYTE

ADDRESS (HEX)

0x00

0x01

0x02

0x03

0x04

0x05

0x06

0x07

0x08

0xFF

FUNCTION

Input port 1

Input port 2

Output port 1

Output port 2

Port 1 polarity inversion

Port 2 polarity inversion

Port 1 configuration

Port 2 configuration

Timeout register

Factory reserved. (Do not write to this register.)

PROTOCOL

Read byte

Read byte

Read/write byte

Read/write byte

Read/write byte

Read/write byte

Read/write byte

Read/write byte

Read/write byte

—

POWER-UP

DEFAULT

XXXX XXXX

XXXX XXXX

1111 1111

1111 1111

0000 0000

0000 0000

1111 1111

1111 1111

0000 0001

—

SCL

123456789

COMMAND BYTE

PORT 1 DATA

PORT 2 DATA

SDA S

SLAVE ADDRESS

A 0 0 0 0 0 0 1 0A 7 6 5 4 3 2 1 0A 7 6 5 4 3 2 1 0 A

START

CONDITION

R/W

ACKNOWLEDGE

FROM SLAVE

ACKNOWLEDGE

FROM SLAVE

ACKNOWLEDGE

FROM SLAVE

ACKNOWLEDGE

FROM SLAVE

WRITE TO PORT

DATA OUT PORT 1

tPV

READ FROM PORT 2

tPV

Figure 7. Writes to Output Registers Through Write Byte Protocol

8 _______________________________________________________________________________________

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