The PCA9674 and PCA9674A provides general purpose remote I/O expansion via the two-line bidirectional I²C‑bus (serial clock (SCL), serial data (SDA)).
The devices consist of eight quasi-bidirectional ports, 1 MHz I²C‑bus Fast-mode Plus
(Fm+) family interface, with high speed data transfer it can support PWM dimming of
LEDs, and higher I²C‑bus drive 30 mA for more devices can be on the bus without the
need for bus buffers. Three hardware address inputs and interrupt output operating
between 2.3 V and 5.5 V. The quasi-bidirectional port can be independently assigned as
an input to monitor interrupt status or keypads, or as an output to activate indicator
devices such as LEDs. The system master can read from the input port or write to the
output port through a single register.
The low current consumption of 4.5 μA (typical, static) is great for mobile applications and
the latched output ports have 25 mA high current sink drive capability for directly driving
The PCA9674 and PCA9674A are identical except for the different, non-overlapping slave
address. The three hardware selectable address pins can be decode to 64 addresses for
the PCA9674 and 62 addresses for the PCA9674A, so there can be up to 126 of these I/O
expanders PCA9674/74A together on the same I²C‑bus without the need for bus buffers,
supporting up to 1008 I/Os (for example, 1008 LEDs).
The active LOW open-drain interrupt output (INT) can be connected to the interrupt logic
of the microcontroller and is activated when any input state differs from its corresponding
input port register state. It is used to indicate to the microcontroller that an input state has
changed and the device needs to be interrogated without the microcontroller continuously
polling the input register via the I²C‑bus.
The internal Power-On Reset (POR) initializes the I/Os as inputs with a weak internal
pull-up 100 μA current source.