I`ve decided to quickly design an ay-3-8912 based sound board for the computer. I have two pieces of the chip, one is used in ZX Spectrum AY-board , the other I`ll use for my own project. The design is a modified ZX Spectrum AY interface. I`ve made some necessary modifications: a different address decoder and clock source. My circuit is based on a “MELODIK” interface seen on the net. There is an opion of using internal LM386 based amplifier (mono, there are goldpin connectors for speaker and volume potentiometer) or direct stereo output: the selection is made using jumpers. I`ll probably stick with amplified mono output though.
The board uses 2 I/O adresses:
1111111101111111b (FF7Fh) :
read mode: check the contents of currently selected register.
write mode: selection of active register (it`s address will be latched internally in AY-3-8912 after this operation)
write mode: Writes new value in a currently selected register.
The device decodes /IOSEL+/IORQ, /WR /RD and A7=0 + A6=1 signals. Function select is made by A0 line.
Below are schematics and board layout design in Eagle. The board isn`t even etched yet, but I hope the design is OK, and the board will work without problems.