TCA7408 Datasheet, PDF (6/25 Pages) Texas Instruments – Low-Voltage 8-Bit I2C and SMBus I/O Expander with Interrupt Output, RESET, I/ODirection Registers, and Programmable Pull-up/Pull-down

TCA7408
SCPS235 – NOVEMBER 2011
DEVICE ADDRESS
The address of the device is shown below
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ADDRESS REFERENCE
ADDR
SLAVE ADDRESS
I²C BUS SLAVE ADDRESS
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
the internal registers that will be affected. This register can be written or read through the I²C bus. The command
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.
Data byte write to
Device ID and Control Register
Data byte write to
Output State Register
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
I/O Direction Register
6
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