Overview
The PCF8574/PCF8574A is a TWI I/O expansion chip with an 8-bit quasi-bidirectional
bi-directional pin. Those two version PCF8574 and PCF8574A are identical in functionalities but they have a different slave address 0x40 (write) for the PCF8574 and 0x70 (write) for the PCF8574A. This chip is very easy to find due to a variety of manufactures such as NXP and Texas Instruments etc.
This chip is applicable for,
- LED signs and displays
- Servers
- Key pads
- Industrial control
- Medical equipment
- PLC
- Cellular telephones
- Mobile devices
- Gaming machines
- Instrumentation and test measurement.
For electronic hobbyists and students this chip is commonly found in an HD44780 LCD controller or even a matrix keypad.
Since it uses TWI its communication protocol could be done from scratch even using a micro-controller without a TWI module inside. Software bit banging is a preferred method for most of programmers since since they don't need to know about the detail of the device's communication protocol. It's user friendly to most hobbyists and students since it has ad DIP package. It's widely available both in a single DIP chip or even in a module at very low cost. Arduino is the most common micro-controller that's very easily to interface and program with this chip.
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| A PCF8574AP DIP |
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| A character LCD with a PCF8574T |
ATMega644 TWI and PCF8574AP
Using the PCF8574AP with an AVR micro-controller could be done from scratch via its TWI or software bit banging. However I have wrote some of its most commonly used routine of hardware TWI in previous post.
