The SON of ZON is a sound synthesizer board with two spare 8 bit I/O ports. It is a more or less a copy of the original ZON board directly compatible with ZON and the wonderful library of sound files available for the Spectrum. The “Eighty-One” emulator for the ZX81 will soon support the ZON board and therefore will be compatible with this sound I/O board as well.
How it works
I won’t go into the details of the sound chip itself but just mention a few details about the interface circuit the adapts the Z80 control signals to the GI chip control line and the multiplexed Address and Data (DA0-DA7) lines.
The CPU 3.25MHz clock is divided by two to drive the AY–8910 chip clock pin with 1.625MHz. The original ZON board used a partially decoded address “Select 60” from an I/O address decoder not shown on the ZON schematic. The SON of ZON decoding of the OF and DF I/O read and write addresses does not require such a “select 60” signal and while the decoding is quite primitive, it is compatible with the original. Note the use of ˝ of the 74LS74 flip-flop as an inverter. Also note that 74HCTxx chips can also be used resulting in some power savings.
Now to find my stash of AY-3-8910/12 chips and try it all out.