== Chip Variants ==
The PSG chip family is composed of 3 variants: the AY-3-8910 with two 8-bit I/O ports, the AY-3-8912 with one 8-bit I/O port and the AY-3-8913 with no I/O port. In addition to the CPC, these chips were also used in the [[KC Compact]], [[ZX Spectrum]], [[MSX]], [[Oric]], [[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 SSG has also been integrated as a component inside some of the arcade soundchips of the Yamaha OPN family. That's why you can find it in the [[Neo-Geo]] as a component inside the YM2610 soundchip. And the same is true for the OPN3 soundchip of the [[Play2CPC]] expansion.
The chip is clocked differently depending on the computer: ZX Spectrum: 1773400 Hz ; Pentagon: 1750000 Hz ; MSX: 1789772 Hz ; CPC: 1000000 Hz ; Atari ST: 2000000 Hz. Toshiba T7766A, Winbond WF19054, JFC 95101 and File KC89C72 are clones of the PSG. [https://wiki.agiri.ninja/sound_chip_clones:index Source]
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.