General Instrument AY-3-8910
The AY-3-8910 is a 3-voice programmable sound generator (PSG) designed by General Instrument (GI) in 1978, initially for use with their 16-bit CP1610 or one of the PIC1650 series of 8-bit microcomputers.
The AY-3-8910 and its variants were used in many arcade games—Konami's Gyruss contains five[1]—and Bally pinball machines as well as being the sound chip in the Intellivision and Vectrex video game consoles, and the Amstrad CPC, Oric-1, Colour Genie, Elektor TV Games Computer, MSX, Tiki 100 and later ZX Spectrum home computers.
It was also used in the Mockingboard and Cricket sound cards for the Apple II and the Speech/Sound Cartridge[2] for the TRS-80 Color Computer.
It was also manufactured under license by Yamaha (with a selectable clock divider pin and a double-resolution and double-rate volume envelope table) as the YM2149F; the Atari ST uses this version.
Its state of sixteen 8-bit registers are programmed over an 8-bit bus (used both for addressing and data) by toggling one of the external pins.
A well known trick was to run the hardware envelope at cycle times above 20 Hz to produce sawtooth or triangle-wave like bass sounds.
There are many new-old-stock (NOS) chips on the secondary market with MSB bits factory set to a non-'0000' value.
Frequencies equivalent to the top octave of a piano keyboard can be defined with reasonable accuracy versus the accepted note values for the even-tempered scale, to nearly 1 Hz precision in the A440 range and even more finely at lower pitches.
Despite the high maximum frequency, the ability to divide that figure by 4096 means the lowest directly definable output frequency is 30.6 Hz, roughly equal to B0, the third lowest note on a normal 88-key piano, and as good as subsonic with everyday speaker systems.
In essence, the chip is able to produce decently musical output at all reasonable pitches found in most compositions.
[3] The Yamaha YM2149F SSG (Software-controlled Sound Generator) 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 AY-3-8914 has the same pinout and is in the same 40-pin package as the AY-3-8910, except the control registers on the chip are shuffled around, and the 'expected input' on the A9 pin may be different.
Its far more advanced successors: the YM2608 (also known as OPNA) and the YM2610 (also known as OPNB), also included the YM2149 core and retained all previous features while greatly expanding upon those, with the YM2610 excluding the I/O ports among other minor changes.
