PCF8574TS/3,118: NXP's Remote 8-Bit I/O Expander for I²C-Bus Applications

In the realm of embedded systems and IoT design, efficiently managing a growing number of sensors, actuators, and indicators without overburdening the main microcontroller is a common challenge. The PCF8574TS/3,118 from NXP Semiconductors provides an elegant and cost-effective solution. This device is a remote 8-bit I/O expander that communicates via the ubiquitous I²C-bus (Inter-Integrated Circuit bus), enabling a single microcontroller to control numerous additional I/O lines with minimal wiring.

The core functionality of the PCF8574TS/3,118 is to add eight quasi-bidirectional I/O ports to any microcontroller that supports the I²C protocol. The quasi-bidirectional architecture simplifies design by eliminating the need for a dedicated direction control register; each pin can be used as an input or an output without explicit configuration. A key advantage of this IC is its extremely simple "set-and-forget" interface. The microcontroller simply reads or writes a single byte of data to the device's register to update or read the state of all eight pins simultaneously.

Operating with a wide voltage range, typically from 2.5V to 6V, the PCF8574TS/3,118 is compatible with various logic levels, enhancing its versatility across different system architectures. Its I²C address is configurable through three hardware address pins (A0, A1, A2), allowing up to eight identical devices to be connected on the same bus, expanding the system by 64 I/O lines using only two microcontroller pins (SDA and SCL).

A critical feature for real-world applications is the open-drain interrupt output pin. This pin actively alerts the microcontroller whenever a change of state is detected on the input pins, eliminating the need for the MCU to continuously poll the device. This significantly reduces software overhead and improves overall system power efficiency.

The PCF8574TS/3,118 is offered in a small TSSOP16 surface-mount package, making it suitable for space-constrained PCB designs. Common applications include driving LEDs, reading DIP switches or keypads, controlling relays, and monitoring digital sensors in industrial control, consumer electronics, and automotive systems.

ICGOODFIND: The PCF8574TS/3,118 remains a fundamental component for system expansion, prized for its simplicity, I²C bus compatibility, and interrupt-driven functionality, making it an indispensable tool for designers needing to extend the I/O capabilities of their embedded projects.

Keywords: I²C-bus, I/O Expander, Quasi-bidirectional, Interrupt Output, NXP.