Changes
8255
,There's no apostrophe for ownership on 'its' (or the other personal pronouns — hers, yours, etc — other than one's)
== 8255 Part numbers used in the CPC during it's its lifetime ==
* NEC D8255AC-2
== The 8255 in the CPC ==
The [[8255 PPI chip]] is a general purpose input/output IC. This document will describe it's its role in the Amstrad CPC, CPC+ and KC compact systems. To understand it's its 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.
* LK1-4 are links on the mainboard ("0" bits are wired to GND). On CPC464,CPC664,CPC6128 and GX4000 they are labeled LK1-LK4, on the CPC464+ and CPC6128+ they are labeled LK101-LK103 (and LK104, presumably?).
* Bit5 (/EXP) can be used by a expansion device to report it's its presence. "1" = device connected, "0" = device not connected. This is not always used by all expansion devices. ''is it used by any expansions?'' [in the DDI-1 disc interface, /EXP connects to the ROM bank selection, bank 0 or bank 7]
* If port B is programmed as an output, you can make a fake vsync visible to the Gate-Array by writing 1 to bit 0. You can then turn it off by writing 0 to bit 0. It is fake in the sense that it is not generated by the CRTC as it normally is. This fake vsync doesn't work on all CPCs. It is not known if it is dependent on CRTC or 8255 or both.
