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I/O

Port

4

5

6

7

9

10

11

12

P0

P1

P2

P3

P4

P5

P6

P7

Shift

Register

8 Bit

LP Filter

Interrupt

Logic

Input

Filter

15

Power-On

Reset

Read Pulse

Write Pulse

PCF8574A

3

2

1

13

16

8

GND

SDA

SCL

A2

A1

A0

INT

Pin numbers shown are for the DW and N packages.

Control

PCF8574A

www.ti.com

SCPS069F – JULY 2001 – REVISED NOVEMBER 2015

8 Detailed Description

8.1 Overview

The PCF8574A device provides general-purpose remote I/O expansion for most microcontroller families via the

The device features an 8-bit quasi-bidirectional I/O port (P0–P7), including latched outputs with high-current drive

capability for directly driving LEDs. Each quasi-bidirectional I/O can be used as an input or output without the use

on when an output is written high and is switched off by the negative edge of SCL. The I/Os should be high

before being used as inputs.

The PCF8574A device provides an open-drain output (INT) that 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

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 bit after the rising edge of the SCL signal, or in the write mode at the

acknowledge bit after the high-to-low transition of the SCL signal. Interrupts that occur during the acknowledge

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, after the next rising clock edge, 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

simple slave device.

8.2 Functional Block Diagram

8.2.1 Simplified Block Diagram of Device

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Product Folder Links: PCF8574A