Description
IDE8255 is the simplest IDE multiplexer (8bit to 16bit) that everyone can build.
It consists of port decoder, a 8255 PPI chip, 74LS139 chip as control gate and some diodes, resistors and capacitors. The most important is, that the 8255 can work in MODE 1 while reading.
MODE 1 automaticly generates read signal for IDE device only by reading PA and PB of 8255, so only one IN per byte is needed. However, writing needs two OUTs per byte.
The IDE8255 for CPC is based on universal YAMOD.IDE8255. For CPC other port addresses are selected.
The IDE8255 borad is intended to be internal upgrade for CPC6128, placed between keyboard and 3" drive. It also can be used as external one, as has 50pin slot for flat cable.