* Uses I/O Port FFxxh (Write only), ie. only /IORQ, /WR, A15-A8 are decoded. A7..A0 are not decoded, and /RD isn't used, too.
* Port usage: Write 8bit unsigned sample data to Port FFxxh. The D/A converter is mono and has only one channel (mixing multiple channels is to be done by software).
* The Amdrum software "probably/reportedly" uses port FF50h .FFxxh.The playback routine also scans the keyboard. which reportedly "needs The lower 8-bits of the I/O port come from the last value of the C register used to be confirmed though". scan the FFh keyboard. Partial dissassembly of player:exx ld a,(bc)add a,(hl)ex de,hladd a,(hl)inc hlex de,hlinc bcadd a,80hinc hlexx out (c),ald b,0f6hin upper 8bit is confirmed a, but not sure if software always uses 50h (c)ld c,axor 05hout (c),ald a,0f4hin lower 8bit? a,(66h)ld (404eh),aout (c),c ld b,0ffhnop nop nop exx ld a,(bc)add a,(hl)ex de,hladd a,(hl)inc hlex de,hlinc bcadd a,80hinc hlexx out (c),a
The five chips on the single-sided PCB are: