1.

General description

The PCA9539; PCA9539R is a 24-pin CMOS device that provides 16 bits of General

Purpose parallel Input/Output (GPIO) expansion with interrupt and reset for

I/O is needed for ACPI power switches, sensors, push buttons, LEDs, fans, etc.

The PCA9539; PCA9539R consists of two 8-bit configuration (input or output selection),

input, output and polarity inversion (active HIGH or active LOW operation) registers. The

system master can enable the I/Os as either inputs or outputs by writing to the I/O

configuration bits. The data for each input or output is kept in the corresponding Input or

Output register. The polarity of the read register can be inverted with the Polarity inversion

register. All registers can be read by the system master.

The PCA9539; PCA9539R is identical to the PCA9555 except for the removal of the

internal I/O pull-up resistor which greatly reduces power consumption when the I/Os are

held LOW, replacement of A2 with RESET and a different address range.

The PCA9539; PCA9539R open-drain interrupt output is activated when any input state

differs from its corresponding input port register state and is used to indicate to the system

master that an input state has changed.

The power-on reset sets the registers to their default values and initializes the device state

machine. In the PCA9539, the RESET pin causes the same reset/default I/O input

state machine in their default state until the RESET input is once again HIGH. This input

initialized by the RESET pin and the internal general-purpose registers remain

configured state so that they can keep any lines in their previously defined state and not

2.

Features

PCA9539; PCA9539R

and reset

Rev. 05 — 28 July 2008

Product data sheet