The PCAL9535A is a low-voltage 16-bit General Purpose Input/Output (GPIO)
expander with interrupt and reset 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 PCAL9535A to interface with
next-generation microprocessors and microcontrollers where supply levels are
dropping down to conserve power.
The PCAL9535A contains the PCA9535 register set of four pairs of 8-bit
configuration, input, output and polarity inversion registers and
additionally, the PCAL9535A 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 PCAL9535A is a pin-to-pin replacement to the PCA9535 and PCA9535A,
however, the PCAL9535A 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 PCAL9535A 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. Therefore, the PCAL9535A can remain a simple
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 machine.
Three hardware pins (A0, A1, A2) select the fixed I2C-bus address and allow up
to eight devices to share I2C-bus/SMBus.