BETAPIN 1 · Hardware address
Address inputA0
Function
Sets bit 0 of the 7-bit I²C address. Tie directly to VCC or GND.
How to connect
Ground all three address inputs for address 0x20.
Electrical note
Keep stable throughout a bus transaction.
8-bit quasi-bidirectional I²C I/O expander
PCF8574 Pinout
Explore PCF8574 pins, signal names, electrical functions and connection guidance for each package.
Package view
16Physical pins
PCF8574NPDIP-16
Manufacturer-referencedTexas Instruments
Pin diagram
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PCF8574NPDIP-16Top view
PCF8574DWSOIC-16Top view
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PIN 2 · Hardware address
Address inputA1
Function
Sets bit 1 of the 7-bit I²C address. Tie directly to VCC or GND.
How to connect
Ground all three address inputs for address 0x20.
Electrical note
Keep stable throughout a bus transaction.
PIN 3 · Hardware address
Address inputA2
Function
Sets bit 2 of the 7-bit I²C address. Tie directly to VCC or GND.
How to connect
Ground all three address inputs for address 0x20.
Electrical note
Keep stable throughout a bus transaction.
PIN 4 · Eight port bits
Quasi-bidirectional I/OP0
Function
Port bit 0. Writing 0 actively sinks; writing 1 releases the pin with its weak current-source pull-up so it can be read as an input.
How to connect
Connect LED cathode; LED anode reaches +5 V through 1 kΩ.
Electrical note
Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
PIN 5 · Eight port bits
Quasi-bidirectional I/OP1
Function
Port bit 1. Writing 0 actively sinks; writing 1 releases the pin with its weak current-source pull-up so it can be read as an input.
How to connect
Connect a pushbutton to GND and leave its output-latch bit HIGH.
Electrical note
Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
PIN 6 · Eight port bits
Quasi-bidirectional I/OP2
Function
Port bit 2. Writing 0 actively sinks; writing 1 releases the pin with its weak current-source pull-up so it can be read as an input.
How to connect
Leave unused pins open with their latch bits HIGH.
Electrical note
Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
PIN 7 · Eight port bits
Quasi-bidirectional I/OP3
Function
Port bit 3. Writing 0 actively sinks; writing 1 releases the pin with its weak current-source pull-up so it can be read as an input.
How to connect
Leave unused pins open with their latch bits HIGH.
Electrical note
Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
PIN 8 · Ground
GroundGND
Function
Supply and signal reference.
How to connect
Connect to controller ground.
PIN 9 · Eight port bits
Quasi-bidirectional I/OP4
Function
Port bit 4. Writing 0 actively sinks; writing 1 releases the pin with its weak current-source pull-up so it can be read as an input.
How to connect
Leave unused pins open with their latch bits HIGH.
Electrical note
Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
PIN 10 · Eight port bits
Quasi-bidirectional I/OP5
Function
Port bit 5. Writing 0 actively sinks; writing 1 releases the pin with its weak current-source pull-up so it can be read as an input.
How to connect
Leave unused pins open with their latch bits HIGH.
Electrical note
Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
PIN 11 · Eight port bits
Quasi-bidirectional I/OP6
Function
Port bit 6. Writing 0 actively sinks; writing 1 releases the pin with its weak current-source pull-up so it can be read as an input.
How to connect
Leave unused pins open with their latch bits HIGH.
Electrical note
Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
PIN 12 · Eight port bits
Quasi-bidirectional I/OP7
Function
Port bit 7. Writing 0 actively sinks; writing 1 releases the pin with its weak current-source pull-up so it can be read as an input.
How to connect
Leave unused pins open with their latch bits HIGH.
Electrical note
Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
PIN 13 · Input-change interrupt
Open-drain interrupt outputINT̅
Function
Asserts LOW after a change on an input port. Reading/writing the port or return to its original state resets the interrupt as described in the data sheet.
How to connect
Pull up with 10 kΩ to +5 V and connect to a 5 V-compatible interrupt input.
Electrical note
Edges during the acknowledge/reset interval may be lost; read the port and debounce buttons.
PIN 14 · I²C interface
I²C clock inputSCL
Function
Standard-mode serial clock, up to 100 kHz.
How to connect
Connect controller SCL with a suitable pull-up to VCC.
PIN 15 · I²C interface
I²C serial dataSDA
Function
Bidirectional open-drain serial data.
How to connect
Connect controller SDA with a suitable pull-up to VCC.
PIN 16 · Supply
Positive supplyVCC
Function
Operates from 2.5 V to 6 V.
How to connect
Use +5 V for this example and 100 nF directly to GND pin 8.
Electrical note
At 5 V, the specified input HIGH threshold is 3.5 V; do not assume a 3.3 V HIGH is sufficient.