The Programmable Sound Generator (PSG) is a sound chip designed by General Instrument (GI) in 1978. The specific model used in the CPC is the AY-3-8912 chip.
The PSG is quite primitive. It is able to output a square wave and/or white noise in three separate sound channels (named Channel A, B and C). Each channel can be used to output tones and/or white noise.
== PSG Part numbers Some other 8-bit systems used in more sophisticated soundchips such as the CPC during its lifetime == * GI AY-3-8912 [https://wwwyoutu.cpcwiki.eube/imgs/c/cc/CPC464_PCB_Top_%28Z70378_MC0046A%29.jpg Source7pONRbIHT_w C64 SID]* GI AY-3-8912A , the [https://wwwyoutu.cpcwiki.eube/imgs/f/f1/CPC6128_PCB_Top_%28Z70290_MC0020B%29.jpg SourceBANwL2sQ0DM NES APU]* Microchip AY-3-8912 and the [https://wwwyoutu.cpcwiki.eube/imgs/c/cf/AmstradCPC464_Z70375_MC0044D_GA40010_PCB_Top.jpg Source-mdjiWBYIqU Gameboy soundchip]* Microchip AY38912/P [https://www.cpcwiki.eu/imgs/5/5e/CPC464Plus_MC0122B_2700-016P-3_PCB_Top.jpg Source] <br>
== I/O Access ==
# set BC1/BDIR to Write Data
# and back to Inactive.
You must use 3 OUTs to send a value to an AY register, even if you don't change registers in the meantime. [https://www.cpcwiki.eu/forum/programming/interesting-walkthrough-video-coding-a-pet-to-play-samples-at-60khz/msg250874/#msg250874 Source]
So you have to enter the data on F4. Then on F6, select the type of data (bdir/bc1>>#10) and validate everything (bdir/bc1>>00). Otherwise, the data in other AY registers becomes corrupted quite quickly.
Consult this article for more information: [[How to access the PSG via PPI]]
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==== Bit 3 When using the volume envelope generator, the volume is always increased from 00h to 0Fh (Continueor vice versa) ==== We can observe that there are only 8 resulting shapes, even though they are selected by using it is not possible to specify a 4-bit value. In other words, we have: shape = 1 if starting/ending point (ves >> 2 == 0like from 00h to 07h) else 7 if (ves >> 2 == 1) else ves & 7.
==== Bit 2 (Attack) ====
This bit is only responsible for the starting point of the envelope and the direction. In other words, we We have:
volume = 0 if attack else 15 # Start at 0 for attack, 15 for decay
direction = 1 if attack else -1 # Upward for attack, downward for decay
When using the volume envelope generator, the volume is always increased from 00h to 0Fh ==== Bit 3 (or vice versaContinue), it is not possible to specify a starting/ending point Bit 1 (like from 00h to 07hAlternate)and Bit 0 (Hold) ==== When bit3 = 0, volume and direction at the end of a period are always 0.
When bit3 ==== Bit 1 (Alternate) , bit1 and Bit 0 (Hold) ====bit0 determine what happens to volume and direction at the end of a period.
When bit3 = 1, these 2 bits determine what happens to volume and direction at the end of a period.=== Algorithm ====
def envelope_step(volume = ~, direction, shape): volume & 0x0F += direction if !(alternate ^ hold)volume > 15 or volume < 0: match shape: case 8 | 12: volume &= 0x0f # direction is unchanged case 10 | 14: direction *= -1 volume += direction case 11 | 13: direction = 0 if hold else ~ volume = 15 case _: direction = 0 volume = 0 return volume, direction & 1 if alternate
=== 0Eh - External Dataregister Port A ===
According to [https://github.com/mamedev/mame/blob/master/src/devices/sound/ay8910.h MAME]: The input to the shift register is bit0 XOR bit3. Bit0 is the output. This was verified on AY-3-8910 and YM2149 chips.
However, the algorithm is described in detail in the [[Media:Microchip ay8930.pdf|AY-8930 datasheet]]. And it disagrees with MAME, the input to the shift register is bit0 XOR bit2. And it seems bit1 is the output.
[[File:AY38910A noise block diagram.png]]
== Chip Variants ==
=== IC models used in CPC === These are the ones known to be used in the CPC by looking at pictures of CPC mainboards. All should operate almost identically. * GI AY-3-8912 [https://www.cpcwiki.eu/imgs/c/cc/CPC464_PCB_Top_%28Z70378_MC0046A%29.jpg Source]* GI AY-3-8912A [https://www.cpcwiki.eu/imgs/f/f1/CPC6128_PCB_Top_%28Z70290_MC0020B%29.jpg Source]* Microchip AY-3-8912 [https://www.cpcwiki.eu/imgs/c/cf/AmstradCPC464_Z70375_MC0044D_GA40010_PCB_Top.jpg Source]* Microchip AY38912/P [https://www.cpcwiki.eu/imgs/5/5e/CPC464Plus_MC0122B_2700-016P-3_PCB_Top.jpg Source] === Other Variants === The PSG chip family is composed of 3 variants: * the AY-3-8910 , with two 8-bit I/O ports, and a 40-pin package* the AY-3-8912 , with one 8-bit I/O port and a 28-pin package* the AY-3-8913 , with no I/O port. and a 24-pin packageIn addition to the CPC, these chips were also used in the [[KC Compact]], [[ZX Spectrum]], [[MSX]], [[Oric-1/Atmos|Oric]], [[EACA EG2000 Colour Genie]], [[Vectrex]], [[Intellivision]] and in the Mockingboard expansion for the [[Apple II]]. There are also PSG clones: Toshiba T7766A, Winbond WF19054, JFC 95101 and File KC89C72. [https://wiki.agiri.ninja/sound_chip_clones:index Source]
Yamaha produced the SSG (Software-controlled Sound Generator) chip family (YM2149F, YM3439, YMZ294, YMZ284, YMZ285) which is a quasi-clone of the PSG. The main difference is that the envelope counter on the PSG has 16 steps. On the SSG it has twice the steps, happening twice as fast. This chip equips the [[Atari ST]], [[Aleste 520EX]] and [https://www.msx.org/wiki/Yamaha_YM2149 some MSX computers]. It is also used in the [[PlayCity]] expansion.
The chip is clocked differently depending on the computer: ZX Spectrum: 1773400 Hz ; Pentagon: 1750000 Hz ; MSX: 1789772 Hz ; CPC: 1000000 Hz ; Oric: 1000000 Hz ; Atari ST: 2000000 Hz.
The PSG chip competed with the DCSG (Digital Complex Sound Generator) chip family (SN76489, SN94624, TMS9919) by Texas Instruments. The DCSG has similar sounding features except that it does not have any envelope control and that its noise generator has its own dedicated channel.
The EPSG (AY-3-8930), used in the Covox Sound Master soundcard on PCs, is a register-compatible evolution of the AY-3-8910:
* The noise tone can be changed by applying an AND and OR mask to the output
<br>=== Competitors ===
The PSG chip competed with the DCSG (Digital Complex Sound Generator) chip family (SN76489, SN94624, TMS9919) by Texas Instruments. The DCSG has similar sounding features except that it does not have any envelope control and that its noise generator has its own dedicated channel. == Datasheets = Replacing the AY-3-8912 in the CPC with an AY-3-8910(A) ===* [[Media:Ay3In case that the AY-891x3-8912 needs to be replaced in the CPC it can become a hurdle these days to get a real AY-3-8912 especially for an acceptable price.pdf| Instead of the original AY-3-891x datasheet]]8912 it's possible to use an AY-3-8910(A) instead with the help of a small adapter board. An open source adapter board can be found here: https://github.com/etomuc/CPC-AY-3-8910-to-8912-adapter* For tips regarding the desoldering of ICs see this Wiki page: [[Media:Ym2149 datasheet.pdf|YM2149 datasheetIC Repair]] <br>
== Links ==
*[http://en.wikipedia.org/wiki/General_Instrument_AY-3-8910 Wikipedia on the PSG]
*[[Media:Ay3-891x.pdf|AY-3-891x datasheet]] [[Media:Ym2149 datasheet.pdf|YM2149 datasheet]]
*[http://quasar.cpcscene.net/doku.php?id=assem:psg Quasar PSG documentation (in french)]
*[https://youtu.be/C4ezcX1W2_Y Mix I] [https://youtu.be/gH57xU9c7dE Mix II] [https://youtu.be/e7V3EMXF97g Mix III] AMSTRAD CPC MUSIC 1 hour
*[https://youtu.be/AhgUwqv2yAE Space Debris - Amstrad CPC Soundtrakker cover] [https://youtu.be/E_plcHyOC_8 RUN! - SID emulation on Amstrad CPC] by [[BSC]]
*[https://nguillaumin.github.io/ym-jukebox/ YM Jukebox] [https://ym.mmcm.ru/ AY Music Collection]
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[[Category:Hardware]]
[[Category:Music and sound| ]][[Category:Video contents]][[Category:CPC Internal Components]]