PCF8575C

www.ti.com

SCPS123F – MARCH 2005 – REVISED JANUARY 2015

8 Detailed Description

8.1 Overview

The PCF8575C provides an open-drain interrupt (INT) output, which can be connected to the interrupt input of a

microcontroller. An interrupt is generated by any rising or falling edge of the port inputs in the input mode. After

is changed to the original setting, or data is read from or written to the port that generated the interrupt. Resetting

occurs in the read mode at the acknowledge (ACK) bit after the rising edge of the SCL signal or in the write

mode at the ACK bit after the falling edge of the SCL signal. Interrupts that occur during the ACK clock pulse can

be lost (or be very short), due to the resetting of the interrupt during this pulse. Each change of the I/Os after

resetting is detected and is transmitted as INT. Reading from or writing to another device does not affect the

interrupt circuit.

By sending an interrupt signal on this line, the remote I/O can inform the microcontroller if there is incoming data

device.

Every data transmission to or from the PCF8575C must consist of an even number of bytes. The first data byte

in every pair refers to port 0 (P07–P00), and the second data byte in every pair refers to port 1 (P17–P10). To

write to the ports (output mode), the master first addresses the slave device, setting the last bit of the byte

containing the slave address to logic 0. The PCF8575C acknowledges and the master sends the first data byte

for P07–P00. After the first data byte is acknowledged by the PCF8575C, the second data byte (P17–P10) is

sent by the master. Once again, the PCF8575C acknowledges the receipt of the data, after which this 16-bit data

is presented on the port lines.

The number of data bytes that can be sent successively is not limited. After every two bytes, the previous data is

overwritten. When the PCF8575C receives the pairs of data bytes, the first byte is referred to as P07–P00 and

the second byte as P17–P10. The third byte is referred to as P07–P00, the fourth byte as P17–P10, and so on.

Before reading from the PCF8575C, all ports desired as input should be set to logic 1. To read from the ports

(input mode), the master first addresses the slave device, setting the last bit of the byte containing the slave

address to logic 1. The data bytes that follow on the SDA are the values on the ports. If the data on the input port

changes faster than the master can read, this data may be lost.

bus to its default state.

PCF8575, PCF8574, PCA9535, and PCA9555, allowing up to eight of these devices, in any combination, to

Copyright © 2005–2015, Texas Instruments Incorporated

Submit Documentation Feedback

11

Product Folder Links: PCF8575C