Description

The standard 40-pin sound chip in the MSX is called the PSG (Programmable Sound Generator). It has several features:

• It can play either a tone or noise on each of its three voices - for details, see the MSX-BASIC PLAY instruction
• It can produce various sound effects when you directly access its registers - for details, see the MSX-BASIC SOUND instruction and this page about programming the PSG registers in ML
• It also controls the Joystick ports and a few other things

Like other parts of the MSX specification, the PSG chip was an off-the-shelf part. In this case the General Instrument AY-3-8910, which can also be found in many other systems of the era. This chip, or one of its clones, can be found in many MSX1 systems. In newer MSX systems, the PSG is often integrated in a chip called the MSX-Engine (or MSX-System).

Note: Yamaha uses the SSG (Software-controlled Sound Generator) appellation in its technical documentations but it is PSG that is used in the MSX standard documentations.

List of fully compatible chips:

• General Instrument AY-3-8910 (often used in MSXs)
• File KC89C72 (used in an Arabic MSX)
• JFC 95101 (not used in MSXs)
• Microchip Technology AY-3-8910A (Microchip Technology is the old semiconductor division of General Instrument)
• Microchip Technology AY8930 (w/ extended features) (not used in MSXs, used in Darky sound cartridge)
• OKI M5255 (not used in MSXs)
• OY-2-8910AC (used in an Arabic MSX)
• Toshiba T7766A (often used in MSXs, either as a separate chip or embedded in the MSX-ENGINE chip)
• WB5300 (rare, not used in MSXs)
• Winbond WF19054 (rarely used in MSXs)
• Yamaha YM2149 (often used in MSXs, either as a separate chip or embedded in the MSX-SYSTEM chip)
• Yamaha YM3439 (not used in MSXs)

Note: The Yamaha YM2149 is called SSG (Software-controlled Sound Generator).

Software compatible chips:

• General Instrument AY-3-8912 (One I/O port only)
• Yamaha YMZ294 (No I/O port)

Note: Some cartridges add or emulate a second PSG. In this case, it needs to be viewed as a Music Expansion.

Software that uses the PSG for BGM and/or SFX.

Stereo

The General Instrument AY-3-8910 outputs the three channels separately, and so do the Yamaha YM2149 and the PSGs integrated in the Toshiba T7937 and Toshiba T9769 MSX-ENGINEs. The Yamaha S3527 MSX-SYSTEM integrated PSG is down-mixed to a single mono channel. The Yamaha S1985 MSX-SYSTEMII mixes the channels into a left and right channel (A: Center, B: Left, C: Right).

Most MSX computers output mono, however some machines pan the channels to center, left and right. On the Toshiba machines the left and right channel are swapped. Daewoo established yet another panning. Below is a table of MSX models with stereo output and the panning of the respective channels.

* = only the Japanese model

External links

• Wikipedia article on the AY-3-8910
• General Instrument AY-3-8910 datasheet
• Yamaha YM2149 datasheet
• Stereo mixer for PSG
• Stereo modification on MSX (Spanish)