Z80/YM2610 interface

The Z80 can read and write to the YM2610 through two pair of "ports". They're usually called Address A, Data A, Address B, Data B. They're respectively linked to the Z80's ports 4, 5, 6 and 7.

• Port A (Z80 ports 4 and 5) concerns the SSG, ADPCM-B, and FM channels 1 and 2.
• Port B (Z80 ports 6 and 7) concerns the ADPCM-A, and FM channels 3 and 4.

Only Data A (Z80 port 5) can be read ?

See YM2610 registers for a complete bit definition of the registers.

The Z80's SDA0 and SDA1 lines are directly connected to the YM2610's A0 and A1 inputs. SDA2 informs NEO-D0 that the IO request is for the YM2610.