Z80 port map

Number	Read	Write
$00	Read sound code from 68k	Clear sound code buffer
$08		NMI enable
$04~$07	YM2610 I/O
$08	Set $F000~$F7FF bank
$09	Set $E000~$EFFF bank
$0A	Set $C000~$DFFF bank
$0B	Set $8000~$BFFF bank
$0C		Reply to 68k
$18		NMI disable

Bank selection is made by reading ports. SNK used an obscure feature of the Z80: when accessing ports, the entire address bus is set, not only the lower 8 bits.

The banks can then be chosen by putting the bank number in B, the port number in C and doing IN A,(C). Or by putting the bank number in A and doing IN A,(Port). (to verify)