1000 0001, 0x02, 0x02, 0x02, …

Command byte:

B7 = 1 enables auto-increment mode

B6 = 0

B5 = 0

B4-B0 = 0 0001 points to Device ID and Control register

Data byte write to

Device ID and Control Register

Data byte write to

I/O Direction Register

Data byte write to

Output State Register

TCA7408

SCPS235

– NOVEMBER 2011

www.ti.com

DEVICE ADDRESS

The address of the device is shown below

ADDRESS REFERENCE

SLAVE ADDRESS

ADDR

B7

B6

B5

B4

B3

B2

B1

B0

0

1

0

0

0

0

1

1

0 (W)

134 (decimal), 86(h)

0

1

0

0

0

0

1

1

1 (R)

135 (decimal), 87(h)

1

1

0

0

0

1

0

0

0 (W)

136 (decimal), 88(h)

1

1

0

0

0

1

0

0

1 (R)

137 (decimal), 89(h)

The last bit of the slave address defines the operation (read or write) to be performed. A high (1) selects a read

operation, while a low (0) selects a write operation.

CONTROL REGISTER AND COMMAND BYTE

Following the successful acknowledgement of the address byte, the bus master sends a command byte, which is

stored in the Control Register in the TCA7408. Five bits of this data byte state the operation (read or write) and

byte is sent only during a write transmission.

AUTO INCREMENT MODE

An automatic increment feature as been added to the control register for block writes. The master can write to all

10 registers with 1 command byte being sent initially. In auto-increment mode the last five bits of the command

byte are automatically incremented after the byte is written and the next data byte is stored in the corresponding

register. Registers are written in the order shown in the register map shown below. Writes attempted to read only

registers do not change the value in the register.

If B7=0, all the data bytes are written to or read from the register defined by B4 through B0 in a non-incremented

fashion. B6 and B5 should always be 0.

6

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© 2011, Texas Instruments Incorporated

Product Folder Link(s) :TCA7408