Ruud
Veteran Member
I'm disassembling the ROMs of the Commodore PC20-III and the PC-1. They are different but have common parts. But I found a piece of code that is driving me mad, more or less:
The comment under the first three lines says it all.
Thank you for any input!
Code:
...
and ah,0C0h ; filter parity and I/O check
shl ah,1 ; xx00 0000 -> x000 0000 (msb ... lsb)
shl ah,1 ; x000 0000 -> 0000 0000
; AH is always zero at this point or am I missing something?
or al,ah
out dx,al
Thank you for any input!