The PCAL6416A is a 16-bit general purpose I/O expander that provides remote I/O
expansion for most microcontroller families via the I²C-bus interface.
NXP I/O expanders provide a simple solution when additional I/Os are needed while
keeping interconnections to a minimum, for example, in battery-powered mobile
applications for interfacing to sensors, push buttons, keypad, etc. In addition to providing
a flexible set of GPIOs, it simplifies interconnection of a processor running at one voltage
level to I/O devices operating at a different (usually higher) voltage level. The PCAL6416A
has built-in level shifting feature that makes these devices extremely flexible in mixed
signal environments where communication between incompatible I/O voltages is required.
Its wide VDD range of 1.65 V to 5.5 V on the dual power rail allows seamless
communications with next-generation low voltage microprocessors and microcontrollers
on the interface side (SDA/SCL) and peripherals at a higher voltage on the port side.
There are two supply voltages for PCAL6416A: VDD(I2C-bus) and VDD(P). VDD(I2C-bus)
provides the supply voltage for the interface at the master side (for example, a
microcontroller) and the VDD(P) provides the supply for core circuits and Port P. The
bidirectional voltage level translation in the PCAL6416A is provided through VDD(I2C-bus).
VDD(I2C-bus) should be connected to the VDD of the external SCL/SDA lines. This indicates
the VDD level of the I²C-bus to the PCAL6416A, while the voltage level on Port P of the
PCAL6416A is determined by the VDD(P).
The PCAL6416A contains the PCA6416A register set of four pairs of 8-bit Configuration,
Input, Output, and Polarity Inversion registers and additionally, the PCAL6416A 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 PCAL6416A is a pin-to-pin
replacement to the PCA6416A, however, the PCAL6416A powers up with all I/O interrupts
masked. This mask default allows for a board bring-up free of spurious interrupts at
At power-on, the I/Os are configured as inputs. However, 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 Input Port register can be inverted with the Polarity Inversion register, saving external
logic gates. Programmable pull-up and pull-down resistors eliminate the need for discrete
The system master can reset the PCAL6416A in the event of a time-out or other improper
operation by asserting a LOW in the RESET input. The power-on reset puts the registers
in their default state and initializes the I²C-bus/SMBus state machine. The RESET pin
causes the same reset/initialization to occur without depowering the part.
The PCAL6416A 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
master 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 PCAL6416A can
remain a simple slave device. The input latch feature holds or latches the input pin state
and keeps the logic values that created the interrupt until the master can service the
interrupt. This minimizes the host’s interrupt service response for fast moving inputs.
The device Port P outputs have 25 mA sink capabilities for directly driving LEDs while
consuming low device current.
One hardware pin (ADDR) can be used to program and vary the fixed I²C-bus address
and allow up to two devices to share the same I²C-bus or SMBus.