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PCF8574T / PCF8574 I²C 8-Bit I/O Port Expander IC SOP-16 – Pack of 5
PCF8574T / PCF8574 I²C 8-Bit I/O Port Expander IC SOP-16 – Pack of 5
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PCF8574T / PCF8574 I²C 8-Bit I/O Port Expander — SOP-16, 2.5–6V, Arduino (5-Pack)
The PCF8574T (SOP-16 SMD) and PCF8574 (DIP-16 through-hole) are 8-bit quasi-bidirectional I/O port expander ICs from NXP Semiconductors. Communicating over I²C with only 2 wires, they add 8 independently controllable GPIO pins to any microcontroller. With 3 hardware address pins, up to 8 PCF8574 devices can share one I²C bus, providing up to 64 additional GPIO pins. They are the standard IC used in LCD backpack modules (HD44780 I²C adapters) and GPIO expansion shields.
Key Specifications
| Parameter | Value |
|---|---|
| I/O Bits | 8 (quasi-bidirectional) |
| Interface | I²C (up to 400kHz fast mode) |
| I²C Address Range | 0x20–0x27 (PCF8574) / 0x38–0x3F (PCF8574A) |
| Supply Voltage | 2.5–6V |
| Output Current (sink) | 25mA per pin |
| Interrupt Output | Active-low open-drain (ĬNT) |
| Package | SOP-16 (SMD) / DIP-16 (through-hole) |
| Operating Temperature | -40°C to +85°C |
| Quantity | 5 pieces |
Why Choose PCF8574T?
- Only 2 wires (I²C) — adds 8 GPIO pins using just SDA and SCL, no extra wiring
- Up to 8 devices per bus — expandable to 64 GPIO pins on a single I²C bus
- Interrupt output — ĬNT pin notifies MCU of input state changes without polling
- 25mA sink current — directly drives LEDs without external transistors
- Standard LCD backpack IC — the same IC used in all HD44780 I²C LCD adapter modules
Compatible With
- Arduino: PCF8574 Arduino library (I²C address 0x20–0x27)
- ESP32 / ESP8266: Wire.h at 3.3V
- STM32: HAL I²C driver
- Raspberry Pi: smbus2 Python library
- LCD modules: HD44780 16×2 and 20×4 character LCD via I²C backpack
Frequently Asked Questions
Q: What is the difference between PCF8574 and PCF8574A?
A: Electrically identical — same 8-bit I/O, same I²C protocol. The only difference is the I²C address range: PCF8574 uses 0x20–0x27, PCF8574A uses 0x38–0x3F. This allows up to 16 devices (8 of each type) on one I²C bus for 128 total GPIO pins.
Q: Can I use PCF8574T to drive a 16x2 LCD over I²C?
A: Yes — this is the most common use case. The PCF8574T is the IC inside all standard HD44780 I²C LCD backpack modules. Wire P0–P7 to the LCD data/control pins and use the LiquidCrystal_I2C Arduino library.
Q: Are the I/O pins truly bidirectional?
A: The PCF8574 uses quasi-bidirectional I/O — each pin has a weak pull-up (100μA) when set HIGH, allowing it to be pulled LOW by an external input. Write 0xFF to set all pins as inputs, then read the register to get input states. For true push-pull output, use the PCA9555 instead.
Package Contents
- 5× PCF8574T I²C 8-Bit I/O Port Expander IC (SOP-16)
