SCPS128D July 2006 – March 2021 PCA9554
Following the successful acknowledgment of the address byte, the bus master sends a command byte that is stored in the control register in the PCA9554. Two bits of this command byte state the operation (read or write) and the internal register (input, output, polarity inversion or configuration) 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.
Once a command byte has been sent, the register that was addressed continues to be accessed by readsuntil a new command byte has been sent.
|CONTROL REGISTER BITS||COMMAND BYTE|
|0||0||0x00||Input Port Register||Read byte||XXXX XXXX|
|0||1||0x01||Output Port Register||Read/write byte||1111 1111|
|1||0||0x02||Polarity Inversion Register||Read/write byte||0000 0000|
|1||1||0x03||Configuration Register||Read/write byte||1111 1111|