PSG
Various PSGs were used in the Intellivision from the AY-3-891x family, including the AY-3-8914, AY-3-8916 and AY-3-8917.
The text below is just a bunch of notes for now, to be organized into something meaningful eventually.
Clock speed is 3579545/16 (223721.5625 Hz)
Registers
Channels
square wave output optionally modified by the envelope generator and/or the noise generator Volume (0-15) Period (1-4096) Tone Enabled Envelope Enabled Noise Enabled
16 volume levels, independent to each channel
if (channel.toneEnabled || channel.noiseEnabled) {
if (
channel
}
else
channel.output = ;
channel0.output =
(((channel0.toneDisabled | channel0.tone) &
(channel0.noiseDisabled | noise))
? (channel0.envelope ? envelopeVolume
: channel0.volume) : 0);
Envelope Generator
Period Atak, Cont, Hold, Altr Volume (0-15) 16-bit period value multiplied by two, from 2 PSG clock cycles to $20000
Noise Generator
The random noise generator adheres to the following formula once per PSG clock cycle.
noise = (noise >> 1) ^ ((noise & 1) ? 0x14000 : 0);
The lowest bit resulting from this calculation is used to add noise to any channel with noise enabled.
