- Pair A (Z80 ports 4 and 5) concerns the SSG, ADPCM-B, and FM channels 1 and 2.
- Pair B (Z80 ports 6 and 7) concerns the ADPCM-A, and FM channels 3 and 4.
See YM2610 registers for a complete definition of the registers.
From Japanese datasheet:
- Address write: 17 cycles (8MHz: 2.125us)
- Data write: 83 cycles (8MHz: 10.375us)
Many original sound drivers use small routines with fixed delays to write to the YM2610:
; DE -> YM2610 pair A ; This also works with pair B (ports 6 & 7) di ld a,d out ($04),a ; At least 21 T-states here ! (6 NOPs, 5.25us) ld a,e out ($05),a ; At least 73 T-states here ! (19 NOPs, 18.25us) ei
Polling the YM2610's busy flag is also a solution.