General Instrument AY-3-8910

The AY-3-8910 is a 3-voice Programmable Sound Generator (PSG) designed by General Instrument, initially for use with their 16-bit CP1610 or one of the PIC1650 series of 8-bit microcomputers. In the 1980s the AY-3-8910 and its variants became popular chips in many arcade games, and home computers, such as the Sinclair ZX Spectrum 128. It was also produced under license by Yamaha as the YM2149, which was used in the Atari ST.

Variants
The IC was sold in three different packages.

The AY-3-8910 has two general-purpose 8-bit parallel I/O ports, A and B, and these are available in the 40-pin package of the same name.

The AY-3-8912 is the same chip in a 28-pin package, with parallel port B simply not connected to any pins. Smaller packages save cost and board space. The 8912 was the most widely-used variant.

The AY-3-8913 is the same chip in a 24-pin package, with both parallel ports not connected. Some users thought the small reduction in pin count over the 8912 made it less interesting, however, the I/O registers were rarely used by designers so General Instruments created this fully functional 24 pin alternative and released it approximately 6 months after the 8910 and 8912 chips. The goal was to reduced complexity for the designer and reduce the foot print on the PCB.

The AY-3-8914, used on the Mattel Intellivision, has the same pinout and is in the same 40-pin package as the 8910, except the control registers on the chip are shuffled around, and the 'expected input' on the A9 pin may be different. Otherwise it is exactly the same as the 8910.

The AY-3-8930, also known as AY8930, is an enhanced but mostly-backwards-compatible version of the 8910. The function of the BC2 pin is changed (it is ignored and assumed to be 0 regardless of the pin state), otherwise the pinout is the same as the 8910. This variant of the chip adds a number of major enhancements, such as separate envelopes for the three channels (as opposed to one shared envelope), variable duty-cycles, more bits of precision for note frequency, volume, and envelope frequency, and a much more configurable noise generator. It was used on the Covox Sound Master sound card for the IBM-PC. Very few games took advantage of it beyond the normal 8910 features. This chip may have only been produced by Microchip Technology.

Yamaha variants
The Yamaha YM2149 'SSG' chip has the same pinout as the AY-3-8910, with the minor difference that pin 26 could halve the master clock if pulled low. If left unconnected, as it would be if replacing an AY-3-8910 chip, an internal resistor pulls the pin high, so the master clock is not halved.

The YM3439 is a CMOS version of the YM2149. It exist in two packages: 40-pin DIP (YM3439-D) and 44-pin QFP (YM3439-F).

The YMZ294 is one of the newest variants of the YM2149, but in a 18-pin package. Has no parallel ports and only one sound output with the three channels mixed.

The YMZ284 is an even smaller variation of the YM2149, in a 16-pin package. It's basically YMZ294 without the 4/8 MHz selection pin and the /TEST pin.

The YMZ285 has a 28-pin package and features a built-in PCM. Has no parallel ports and two sound outputs: one with the three SSG channels mixed, the other with the PCM output.