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
| Register | Data Bits | On Bits | Off Bits | Description |
|---|---|---|---|---|
| $00 | $00FF | $0000 | $FF00 | Lowest 8 bits of 12-bit period for channel 1. Note that a channel period value of zero actually indicates a period of $1000. |
| $01 | $00FF | $0000 | $FF00 | Lowest 8 bits of 12-bit period for channel 2. Note that a channel period value of zero actually indicates a period of $1000. |
| $02 | $00FF | $0000 | $FF00 | Lowest 8 bits of 12-bit period for channel 3. Note that a channel period value of zero actually indicates a period of $1000. |
| $03 | $00FF | $0000 | $FF00 | Lowest 8 bits of 16-bit envelope period. The envelope period value is multiplied by two to determine the actual period. Note that an envelope period value of zero actually indicates a true envelope period of $20000. |
| $04 | $000F | $0000 | $FFF0 | Upper 4 bits of 12-bit period for channels 1. Note that a channel period value of zero actually indicates a period of $1000. |
| $05 | $000F | $0000 | $FFF0 | Upper 4 bits of 12-bit period for channels 2. Note that a channel period value of zero actually indicates a period of $1000. |
| $06 | $000F | $0000 | $FFF0 | Upper 4 bits of 12-bit period for channels 3. Note that a channel period value of zero actually indicates a period of $1000. |
| $07 | $00FF | $0000 | $FF00 | Upper 8 bits of 16-bit envelope period. The envelope period value is multiplied by two to determine the actual period. Note that an envelope period value of zero actually indicates a true envelope period of $20000. |
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
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.
