== The 8255 in the CPC ==
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.
* If you are using the firmware, always return the operating modes and I/O state of the ports used to their settings below. The firmware expects the settings to be the same as given below and may operate incorrectly if they are not.
=== PPI Port A ===
* for reading data from PSG all bits must be set to input.
=== PPI Port B ===
Operating system settings:
* I/O Mode 0,
* Input
Note:
1. On CPC464,CPC664,CPC6128 and GX4000 this is LK3 on the PCB. On the CPC464+ and CPC6128+ this is LK103 on the PCB. On the KC compact this is "1".
2. On CPC464,CPC664,CPC6128 and GX4000 this is LK2 on the PCB. On the CPC464+ and CPC6128+ this is LK102 on the PCB. On the KC compact this is "0".
3. On CPC464,CPC664,CPC6128 and GX4000 this is LK1 on the PCB. On the CPC464+ and CPC6128+ this is LK101 on the PCB. On the KC compact this is /TEST signal from the expansion port.
4. On the CPC464,CPC664,CPC6128,CPC464+,CPC6128+ and GX4000 bits 3,2 and 1 define the manufacturer name. See below to see the options available. The manufacturer name is defined on the PCB and cannot be changed through software.
5. On the CPC464,CPC664,CPC6128,CPC464+,CPC6128+ and GX4000 bit 4 defines the Screen refresh frequency. "1" = 50Hz, "0" = 60Hz. This is defined on the PCB and cannot be changed with software. On the KC compact bit 4 is "1"
6. This bit is connected to /EXP signal on the expansion port.
* On the KC Compact this bit is used to define bit 7 of the printer data.
* On the CPC, it is possible to use this bit to define bit 7 of the printer data, so a 8-bit printer port is made, with a hardware modification,
* On the CPC this can be used by a expansion device to report it's presence. "1" = device connected, "0" = device not connected. This is not always used by all expansion devices.
Table showing manufacturer name on power-up (CPC and CPC+ only):
[Image:8255 ppi 1.jpg]]
= Resources ==
[[Media: |Datasheet of the 8255]]