PCF8574 Reference Tables, Pins & Specifications | The Engineering Projects

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Selected packagePDIP-16PCF8574N

Physical connections16 pinsPackage-specific numbering

Reference collection8 tables49 parameters & pin functions

Pin reference

Signal names, electrical functions and connection guidance

PDIP-16

Physical pin numbers16 pins

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PCF8574 pin functions and connections
Pin	Signal	Type	Function & connection
	A0	Address input	Sets bit 0 of the 7-bit I²C address. Tie directly to VCC or GND. Connection guidance Ground all three address inputs for address 0x20. Keep stable throughout a bus transaction.
	A1	Address input	Sets bit 1 of the 7-bit I²C address. Tie directly to VCC or GND. Connection guidance Ground all three address inputs for address 0x20. Keep stable throughout a bus transaction.
	A2	Address input	Sets bit 2 of the 7-bit I²C address. Tie directly to VCC or GND. Connection guidance Ground all three address inputs for address 0x20. Keep stable throughout a bus transaction.
	P0	Quasi-bidirectional I/O	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. Connection guidance Connect LED cathode; LED anode reaches +5 V through 1 kΩ. Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
	P1	Quasi-bidirectional I/O	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. Connection guidance Connect a pushbutton to GND and leave its output-latch bit HIGH. Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
	P2	Quasi-bidirectional I/O	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. Connection guidance Leave unused pins open with their latch bits HIGH. Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
	P3	Quasi-bidirectional I/O	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. Connection guidance Leave unused pins open with their latch bits HIGH. Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
	GND	Ground	Supply and signal reference. Connection guidance Connect to controller ground.
	P4	Quasi-bidirectional I/O	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. Connection guidance Leave unused pins open with their latch bits HIGH. Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
	P5	Quasi-bidirectional I/O	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. Connection guidance Leave unused pins open with their latch bits HIGH. Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
	P6	Quasi-bidirectional I/O	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. Connection guidance Leave unused pins open with their latch bits HIGH. Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
	P7	Quasi-bidirectional I/O	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. Connection guidance Leave unused pins open with their latch bits HIGH. Not a conventional push-pull HIGH output; preserve input bits as 1 in every output write.
	INT̅	Open-drain interrupt output	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. Connection guidance Pull up with 10 kΩ to +5 V and connect to a 5 V-compatible interrupt input. Edges during the acknowledge/reset interval may be lost; read the port and debounce buttons.
	SCL	I²C clock input	Standard-mode serial clock, up to 100 kHz. Connection guidance Connect controller SCL with a suitable pull-up to VCC.
	SDA	I²C serial data	Bidirectional open-drain serial data. Connection guidance Connect controller SDA with a suitable pull-up to VCC.
	VCC	Positive supply	Operates from 2.5 V to 6 V. Connection guidance Use +5 V for this example and 100 nF directly to GND pin 8. At 5 V, the specified input HIGH threshold is 3.5 V; do not assume a 3.3 V HIGH is sufficient.

Port behavior

Quasi-bidirectional operation

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
Latch bit 0	Active LOW sink	Suitable for sinking a current-limited LED
Latch bit 1	Weak current-source HIGH	Can be pulled LOW externally and used as input
Power-on state	All latch bits HIGH	Pins behave as inputs with weak HIGH sources
Direction registers	None	Direction follows the output-latch state
Read value	Actual terminal levels	May differ from the software output shadow
Output update	Whole 8-bit byte	Keep all input bits HIGH in every write

HIGH is not a sustained strong push-pull output. The temporary strong pull-up assists a rising edge only.

Address selection

7-bit addresses; do not include the R/W bit

Manufacturer-referenced values8 parameters

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Parameter	Value	Conditions / notes
A2 A1 A0 = 000	0x20	Write byte 0x40 · read byte 0x41
A2 A1 A0 = 001	0x21	Write byte 0x42 · read byte 0x43
A2 A1 A0 = 010	0x22	Write byte 0x44 · read byte 0x45
A2 A1 A0 = 011	0x23	Write byte 0x46 · read byte 0x47
A2 A1 A0 = 100	0x24	Write byte 0x48 · read byte 0x49
A2 A1 A0 = 101	0x25	Write byte 0x4a · read byte 0x4b
A2 A1 A0 = 110	0x26	Write byte 0x4c · read byte 0x4d
A2 A1 A0 = 111	0x27	Write byte 0x4e · read byte 0x4f

PCF8574A has a different address block. This page uses PCF8574.

Example byte transfers

Address pins grounded · 7-bit address 0x20

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
LED off; inputs released	Write 0xFF	All port latches HIGH
LED on at P0	Write 0xFE	P0 LOW; P1–P7 remain HIGH
Read the button	Read one byte; inspect bit 1	P1 LOW when the grounded button is pressed
Typical pressed read with LED on	0xFC	Assumes other released inputs read HIGH
Transfer structure	START → address → data → STOP	No register-address byte
INT servicing	Read port, process changes, debounce	Read/write or return to original state can reset INT

The example values describe the stated wiring. Do not use a read byte as an unfiltered output-latch shadow.

Electrical limits

Recommended operation unless marked otherwise

Manufacturer-referenced values9 parameters

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Parameter	Value	Conditions / notes
VCC	2.5–6 V	Example uses 5 V
Input HIGH / LOW	≥ 0.7 VCC / ≤ 0.3 VCC	Supply-dependent logic thresholds
P-port weak HIGH source	30–310 µA magnitude	At VO = GND, VCC 2.5–6 V
P-port sink	10 mA minimum; 25 mA typical	At VCC 5 V, VO 1 V
Recommended LOW current	25 mA maximum per port	Observe total device and thermal limits
SDA sink	3 mA minimum	At VOL 0.4 V
INT sink	1.6 mA minimum	At VOL 0.4 V
Standby supply current	2.5 µA typical; 10 µA maximum	VCC 6 V; inputs at rails; unloaded
Operating supply current	40 µA typical; 100 µA maximum	VCC 6 V; 100 kHz clock; unloaded

Do not interpret the absolute 50 mA port rating as a design target.

Bus timing and pull-ups

Standard-mode I²C

Manufacturer-referenced values7 parameters

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Parameter	Value	Conditions / notes
SCL frequency	100 kHz maximum	Not a 400 kHz fast-mode expander
SCL LOW / HIGH	4.7 µs / 4.0 µs minimum	Timing requirements
SDA setup	250 ns minimum	Before SCL rises
Bus rise time	1 µs maximum	Choose pull-ups for capacitance and sink current
Maximum bus capacitance	400 pF	Requires a compatible pull-up value
Example pull-ups	4.7 kΩ on SDA and SCL	About 0.40 µs rise at an assumed 100 pF
Port / interrupt delay	4 µs maximum	Specified switching-test conditions

The example 4.7 kΩ is a starting value for a short bus, not a guarantee at the full 400 pF limit.

Button and LED connections

5 V controller and expander

Manufacturer-referenced values7 parameters

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Parameter	Value	Conditions / notes
Supply	VCC16 +5 V; GND8 common	100 nF local bypass
Address	A0 pin1, A1 pin2, A2 pin3 to GND	Selects 0x20
SDA15 / SCL14	Controller I²C bus	Each has a 4.7 kΩ pull-up to +5 V
INT13	Controller interrupt input	10 kΩ pull-up to +5 V
P0 pin4	LED cathode	Anode via 1 kΩ to +5 V; LOW turns it on
P1 pin5	Pushbutton to GND	Write latch bit 1 before reading; debounce
P2–P7	Unused in this example	Leave open and maintain latch bits HIGH

At assumed VF 2 V and VOL 0.2 V, LED current is (5 − 2 − 0.2)/1k = 2.8 mA. Actual values depend on the LED and port.

Package selection and stress limits

PCF8574N · PDIP-16

Manufacturer-referenced values6 parameters

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Parameter	Value	Conditions / notes
N package	PDIP-16; 2.54 mm pitch	Through-hole view shown
DW package	Wide SOIC-16; 1.27 mm pitch	7.5 mm nominal body width
PW / DGV alternatives	20 physical leads	Different mapping with unused pins; not shown
VCC absolute maximum	6.5 V	Normal recommended maximum is 6 V
Continuous supply/ground current	±100 mA absolute maximum	Stress rating; sum all loads
Storage temperature	−65 to +150°C	Unpowered

The two selected 16-pin packages share logical pin numbering but require different PCB footprints.