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.
This will cause an invalid PSG register to be selected:
ld bc,&f400
out (c),c
ld bc,&f6c0
out (c),c
ld bc,&f792
out (c),c
;; At this point FF appears in emulated 8255 port A. This selects an invalid PSG register '&ff', when read &FF is returned. This is one source of keyboard reading bugs.
Therefore use this:
ld bc,&f400
out (c),c
ld bc,&f6c0
out (c),c
ld bc,&f600 ;;; << use inactive
out (c),c
ld bc,&f792
out (c),c
* 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===
