8255 PPI IBM PC Interface Card


The 8255 Programmable Peripheral Interface (PPI) is a versatile and easy to construct circuit card the plugs into an available slot in your IBM PC. Such a card allows you to do both digital input and output (DIO) to your PC. For example, you may want to have your PC turn on a switch, or have a switch electronically activate your PC to execute a program. The 8255 has 3 8-bit TTL-compatiable I/O ports. Thus technically you could control up to 24 individual devices. For example, with the circuit description that follows, you could build a home security device, with a digital input detecting if someone rang your doorbell, and having a digital output turning on a light switch, the other remaining 22 DIOs could then be used to detect for sound detection (broken glass say), doors being opened, digitally dial 911, detect smoke etc. Hopefully this preamble has excited your curiosity and imagination. This article is broken down as follows: