General description
The PCF8574/74A provides general-purpose remote I/O expansion via the two-wire bidirectional I2C-bus (serial clock (SCL), serial data (SDA)).
The devices consist of eight quasi-bidirectional ports, 100 kHz I2C-bus interface, three hardware address inputs and interrupt output operating between 2.5 V and 6 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. System master can read from the input port or write to the output port through a single register. The low current consumption of 2.5 μA (typical, static) is great for mobile applications and the latched output ports directly drive LEDs.
The PCF8574 and PCF8574A are identical, except for the different fixed portion of the slave address. The three hardware address pins allow eight of each device to be on the same I2C-bus, so there can be up to 16 of these I/O expanders PCF8574/74A together on the same I2C-bus, supporting up to 128 I/Os (for example, 128 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.

FEATUREs and benefits
■ I2C-bus to parallel port expander
■ 100 kHz I2C-bus interface (Standard-mode I2C-bus)
■ Operating supply voltage 2.5 V to 6 V with non-overvoltage tolerant I/O held to VDD
   with 100 μA current source
■ 8-bit remote I/O pins that default to inputs at power-up
■ Latched outputs directly drive LEDs
■ Total package sink capability of 80 mA
■ Active LOW open-drain interrupt output
■ Eight programmable slave addresses using three address pins
■ Low standby current (2.5 A typical)
■ -40 °C to +85 °C operation
■ ESD protection exceeds 2000 V HBM per JESD22-A114 and 1000 V CDM per
   JESD22-C101