Changes
8255
,/* PPI Port B */
* Bit5 (/EXP) 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. ''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.
