Difference between revisions of "8255"

From CPCWiki - THE Amstrad CPC encyclopedia!
Jump to: navigation, search
Line 18: Line 18:
 
|}
 
|}
  
 +
It is advised that the remaining bits of the I/O address are set to "1" to avoid conflict with other devices. The recommended I/O addressess are:
  
[[Image:8255 ppi 1.jpg]]
+
{|{{Prettytable|width: 700px; font-size: 2em;}}
 +
|''I/O address''||''PPI Function''
 +
|-
 +
|&F4xx||Port A data
 +
|-
 +
|&F5xx||Port B data
 +
|-
 +
|&F6xx||Port C data
 +
|-
 +
|&F7xx||Control
 +
|-
 +
|}
 +
 
 +
In the CPC+, the 8255 is integrated into the ASIC. The "emulation" is not complete and some functionality is not available. Please see the "Extra CPC+ documentation" for more information.
 +
 
 +
* Mode 1 (Strobed Input/Output) and Mode 2 (Bi-Directional Bus), as far as I know, are not used by any program, Mode 0 (Basic Input/Output) is always used.
 +
 
 +
=== Port Usage ===
 +
 
 +
NOTE
 +
 
 +
* 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 ===
 +
 
 +
Operating system settings:
 +
 
 +
* I/O Mode 0,
 +
* Output
 +
 
 +
NOTE:
 +
 
 +
* For writing data to PSG all bits must be set to output,
 +
* for reading data from PSG all bits must be set to input.
 +
 
 +
 
 +
[Image:8255 ppi 1.jpg]]
 
= Resources ==  
 
= Resources ==  
  

Revision as of 04:07, 30 March 2008

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

It is advised that the remaining bits of the I/O address are set to "1" to avoid conflict with other devices. The recommended I/O addressess are:

I/O address PPI Function
&F4xx Port A data
&F5xx Port B data
&F6xx Port C data
&F7xx Control

In the CPC+, the 8255 is integrated into the ASIC. The "emulation" is not complete and some functionality is not available. Please see the "Extra CPC+ documentation" for more information.

  • Mode 1 (Strobed Input/Output) and Mode 2 (Bi-Directional Bus), as far as I know, are not used by any program, Mode 0 (Basic Input/Output) is always used.

Port Usage

NOTE

  • 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

Operating system settings:

  • I/O Mode 0,
  • Output

NOTE:

  • For writing data to PSG all bits must be set to output,
  • for reading data from PSG all bits must be set to input.


[Image:8255 ppi 1.jpg]]

Resources =

[[Media: |Datasheet of the 8255]]

Links

about the 8255ppi