The NXP PCF8574N is an 8-bit I2C I/O expander in a 16-pin DIP package, designed to add remote GPIO to a microcontroller over a two-wire serial bus. It handles eight push-pull I/O lines that can be individually configured as inputs or outputs, with a dedicated interrupt output pin that signals the host when an input state changes. The 100 kHz I2C clock rate matches the original standard-mode specification, so it integrates cleanly into legacy or low-speed bus topologies without requiring clock-stretching support on the master side.
The output stage sinks 25 mA per pin but sources only 1 mA — a common asymmetry in this expander family. For inputs, the port read-back works with open-drain or push-pull signals as long as the voltage stays within the supply rails.
Package and mounting — through-hole for retrofit and prototyping
The 16-DIP (0.300" body width) and 16-PDIP supplier package are the same footprint — a 300-mil wide through-hole DIP. This is the package that fits a breadboard, a perforated prototyping board, or a legacy PCB originally laid out for a 74HC595 or similar parallel expander. The through-hole body also handles moderate vibration environments better than a fine-pitch SMD part when conformal-coated, though the industrial temperature rating (-40°C to 85°C) is the real environmental limit.