It is therefore possible to simulate split screen, by setting the soft scroll at the time correct time, then setting it back to 0 immediately after.
===8255===
* When switching port A of ASICs emulated 8255 to input, FF is present on the emulated 8255's port A outputs.
* When switching input/output of port A, on a normal 8255, the outputs are all cleared to 0. This doesn't happen on the emulated 8255. This is another source of keyboard reading bugs.
===Automatic feeding of sound generator===
An automatic process has been added to feed data to the sound generator from three instruction streams in main RAM without CPU intervention. Three separate channels each fetch one 16-bit instruction during horizontal retrace time. These instructions must be in usual Z-80 format, i.e. least significant bit first and must be aligned to word boundaries (i.e. address of first byte must be even). Once the three instructions have been captured , they are then executed sequentially. The maximum achievable update rate to the PSG is thus equal to the horizontal scan rate of 15.625 kHz per channel.