The 8255 is a general purpose input/output IC. This document will describe it's role in the Amstrad CPC,CPC+ and KC compact systems. To understand it's full functions please read the datasheet.
In these systems it is connected to the AY-3-8912 Programmable Sound Generator (PSG), keyboard, cassette recorder, the VSYNC of the 6845 CRTC and the "busy" signal from the parallel port.
The PPI is selected when bit 11 of the I/O port address is set to "0", bits 9 and 8 then define the PPI function access as shown below:
| Bit 9 | Bit 8 | Description | Read/Write status |
| 0 | 0 | Port A Data | Read/Write |
| 0 | 1 | Port B Data | Read/Write |
| 1 | 0 | Port C Data | Read/Write |
| 1 | 1 | Control | Write Only |
Resources =
[[Media: |Datasheet of the 8255]]