PCF8574 Remote 8-Bit I/O Expander for I2C Bus
General-purpose 8-bit quasi-bidirectional I/O expander for the two-line bidirectional I2C-bus with open-drain interrupt output, widely used in HD44780 LCD I2C backpacks.
Aliase:PCF8574P, PCF8574T, PCF8574A, LCD I2C Backpack Chip
DIP-16 / SO16 Top View
16 Pins
Pinout Table16
| Pin | Signal / Name | Type | Alternative Functions |
|---|---|---|---|
| 1 | A0 | Digital | I2C Address Bit 0 — sets bit 0 of device address (base 0x20 for PCF8574, 0x38 for PCF8574A) |
| 2 | A1 | Digital | I2C Address Bit 1 — sets bit 1 of device address |
| 3 | A2 | Digital | I2C Address Bit 2 — sets bit 2 of device address; A0=A1=A2=0 → base 0x20 (PCF8574) or 0x38 (PCF8574A); range 0x20–0x27 / 0x38–0x3F |
| 4 | P0 | Digital | Quasi-bidirectional I/O 0 (LCD RS on standard backpack) |
| 5 | P1 | Digital | Quasi-bidirectional I/O 1 (LCD R/W on standard backpack) |
| 6 | P2 | Digital | Quasi-bidirectional I/O 2 (LCD E on standard backpack) |
| 7 | P3 | Digital | Quasi-bidirectional I/O 3 (LCD Backlight) |
| 8 | VSS | Ground | Ground (0V) |
| 9 | P4 | Digital | Quasi-bidirectional I/O 4 (LCD D4 on standard backpack) |
| 10 | P5 | Digital | Quasi-bidirectional I/O 5 (LCD D5 on standard backpack) |
| 11 | P6 | Digital | Quasi-bidirectional I/O 6 (LCD D6 on standard backpack) |
| 12 | P7 | Digital | Quasi-bidirectional I/O 7 (LCD D7 on standard backpack) |
| 13 | ~INT | Digital | Interrupt Output (Open-drain, Active Low) |
| 14 | SCL | Digital | I2C Serial Clock Line (max 100 kHz standard) |
| 15 | SDA | Digital | I2C Serial Data Line (Open-drain) |
| 16 | VDD | Power | Supply Voltage (+2.5V to +6.0V DC) |