The PCF8575 is a silicon CMOS circuit. It provides general purpose remote I/O expansion for most microcontroller families via the two-line bidirectional bus (I²C-bus).
The device consists of a 16-bit quasi-bidirectional port and an I²C-bus interface. The PCF8575 has a low current consumption and includes latched outputs with high current drive capability for directly driving LEDs. It also possesses an interrupt line (INT) which can be connected to the interrupt logic of the microcontroller. By sending an interrupt signal on this line, the remote I/O can inform the microcontroller if there is incoming data on its ports without having to communicate via the I²C-bus. This means that the PCF8575 is an I²C-bus slave transmitter/receiver.
Every data transmission from the PCF8575 must consist of an even number of bytes, the first byte will be referred to as P07 to P00 and the second byte as P17 to P10. The third will be referred to as P07 to P00 and so on.