The PCAL9555A is a low-voltage 16-bit General Purpose Input/Output (GPIO) expander
with interrupt and weak pull-up resistors for I²C-bus/SMBus applications. NXP® I/O
expanders provide a simple solution when additional I/Os are needed while keeping
interconnections to a minimum, for example, in ACPI power switches, sensors, push
buttons, LEDs, fan control, etc.
In addition to providing a flexible set of GPIOs, the wide VDD range of 1.65 V to 5.5 V
allows the PCAL9555A to interface with next-generation microprocessors and
microcontrollers where supply levels are dropping down to conserve power.
The PCAL9555A contains the PCA9555 register set of four pairs of 8-bit Configuration,
Input, Output, and Polarity Inversion registers, and additionally, the PCAL9555A has
Agile I/O, which are additional features specifically designed to enhance the I/O. These
additional features are programmable output drive strength, latchable inputs,
programmable pull-up/pull-down resistors, maskable interrupt, interrupt status register,
programmable open-drain or push-pull outputs.
The PCAL9555A is a pin-to-pin replacement to the PCA9555, however, the PCAL9555A
powers up with all I/O interrupts masked. This mask default allows for a board bring-up
free of spurious interrupts at power-up.
The PCAL9555A open-drain interrupt (INT) output is activated when any input state differs
from its corresponding Input Port register state and is used to indicate to the system
that an input state has changed.
INT can be connected to the interrupt input of a 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. Thus, the PCAL9555A can
remain a simple follower device.
The device outputs have 25 mA sink capabilities for directly driving LEDs while consuming
low device current.
The power-on reset sets the registers to their default values and initializes the device state
The device powers on with weak pull-up resistors enabled that can replace external
Three hardware pins (A0, A1, A2) select the fixed I²C-bus address and allow up to eight
devices to share the same I²C-bus/SMBus.