PCF8574DW

I/o Expanders Overview

The PCF8574DW is an 8-bit I/O expander for the two-line bidirectional I2C bus, designed for VCC operation between 2.5V and 6V. It provides general-purpose remote I/O expansion via SCL and SDA pins. The device features an 8-bit quasi-bidirectional I/O port (P0–P7) with latched outputs capable of directly driving LEDs. Each pin functions as input or output without a data-direction control signal; at power-on, I/Os are high. An open-drain interrupt output (INT) signals incoming data changes to the microcontroller. The SOIC-16 package measures 10.3mm x 10.3mm.

I/o Expanders Feature Summary

• I2C to parallel-port expander
• Open-drain interrupt output
• Latched outputs with high-current drive capability

I/o Expanders Applications

• Telecom shelters: filter units
• Servers
• Routers (telecom switching equipment)
• Personal computers
• Industrial automation

I/o Expanders Procurement Notes

Verify the specific ordering suffix against the manufacturer's current datasheet to confirm package type and temperature range. Ensure the component matches the required voltage and interface specifications for the target application before procurement.

I/o Expanders Selection Notes

Select this component when GPIO resources are limited on the host microcontroller. Verify that the I2C bus capacitance does not exceed 400 pF and that pull-up resistors are appropriately sized for the operating voltage and clock frequency requirements.

I/o Expanders Part Context

This part belongs to the PCF8574 family of remote 8-bit I/O expanders. Variants include different packages such as PDIP, TSSOP, TVSOP, and VQFN. The DW suffix specifically denotes the SOIC surface-mount package configuration.

I/o Expanders Replacement Considerations

PCF8574APWRE4

I/o Expanders FAQ

How is the direction of the P0-P7 pins determined?

The pins are quasi-bidirectional and do not have a separate direction register. The direction is implicitly determined by the value written to the data register: writing a 1 sets the pin to high-impedance input mode, while writing a 0 sets it to output mode.

What triggers the INT interrupt output?

An interrupt is generated by any rising or falling edge of the port inputs when they are in input mode. The INT line goes low to signal the microcontroller of the change.

How is the interrupt circuit reset?

Resetting occurs when data on the port is changed back to the original setting, or when data is read from or written to the port that generated the interrupt.