Difference between revisions of "PSG"
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==Registers== | ==Registers== | ||
| + | <table border> | ||
| + | <tr><th>Register</th><th>Data Bits</th><th>On Bits</th><th>Off Bits</th><th>Description</th></tr> | ||
| + | |||
| + | <tr><td>[[STIC Register $00|$00]]</td><td>$00FF</td><td>$0000</td><td>$FF00</td><td>Lowest 8 bits of 12-bit period for channel 1. Note that a channel period value of zero actually indicates a period of $1000.</td></tr> | ||
| + | |||
| + | <tr><td>[[STIC Register $01|$01]]</td><td>$00FF</td><td>$0000</td><td>$FF00</td><td>Lowest 8 bits of 12-bit period for channel 2. Note that a channel period value of zero actually indicates a period of $1000.</td></tr> | ||
| + | |||
| + | <tr><td>[[STIC Register $02|$02]]</td><td>$00FF</td><td>$0000</td><td>$FF00</td><td>Lowest 8 bits of 12-bit period for channel 3. Note that a channel period value of zero actually indicates a period of $1000.</td></tr> | ||
| + | |||
| + | <tr><td>[[STIC Register $03|$03]]</td><td>$00FF</td><td>$0000</td><td>$FF00</td><td>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.</td></tr> | ||
| + | |||
| + | <tr><td>[[STIC Register $07|$04]]</td><td>$000F</td><td>$0000</td><td>$FFF0</td><td>Upper 4 bits of 12-bit period for channels 1. Note that a channel period value of zero actually indicates a period of $1000.</td></tr> | ||
| + | |||
| + | <tr><td>[[STIC Register $07|$05]]</td><td>$000F</td><td>$0000</td><td>$FFF0</td><td>Upper 4 bits of 12-bit period for channels 2. Note that a channel period value of zero actually indicates a period of $1000.</td></tr> | ||
| + | |||
| + | <tr><td>[[STIC Register $07|$06]]</td><td>$000F</td><td>$0000</td><td>$FFF0</td><td>Upper 4 bits of 12-bit period for channels 3. Note that a channel period value of zero actually indicates a period of $1000.</td></tr> | ||
| + | |||
| + | <tr><td>[[STIC Register $07|$07]]</td><td>$00FF</td><td>$0000</td><td>$FF00</td><td>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.</td></tr> | ||
| + | |||
| + | </table> | ||
==Channels== | ==Channels== | ||
Revision as of 20:46, 20 January 2005
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.
