AY-3-8912

The AY-3-8912 is functionally identical to the AY-3-8910 but in a smaller 28-pin package with only one I/O port instead of two. This made it the chip of choice for the ZX Spectrum 128K where board space was at a premium.

Fast facts

• Sound: identical to AY-3-8910.
• Package: 28-pin DIP (vs 40-pin for 8910).
• I/O ports: 1 (vs 2 for 8910).
• Primary use: ZX Spectrum 128K, +2, +3.

Key difference

Feature	AY-3-8910	AY-3-8912
Pin count	40	28
I/O Port A	Yes	Yes
I/O Port B	Yes	No
Chip-select input A9	Yes	Not provided
Sound quality	Identical	Identical
Registers	R0-R15	R0-R15 (R15 drives nothing)

Port B is the difference everyone names, but the 28-pin package also drops the A9 chip-select input. General Instrument offered A8 and A9 as “extra” address bits for placing several PSGs on one bus; the 8912 keeps A8 and loses A9.

Reading the original data sheet? General Instrument numbers its registers in octal. The sheet’s “Envelope Generator Control R13–R15” means decimal R11–R13, and its “Amplitude Control R10–R12” means decimal R8–R10. Taken as decimal they would collide with the I/O ports.

Why it matters

For game programmers, the distinction is largely irrelevant—the sound registers and capabilities are identical. The choice between 8910 and 8912 was a hardware design decision based on available board space and I/O requirements.

Family variants

The AY-3-8910 family covers three pin-counts plus a Yamaha clone:

Chip	I/O	Pins	Notes
AY-3-8910	A + B	40	Original — see AY-3-8910
AY-3-8912	A only	28	Spectrum 128K, CPC, Oric
AY-3-8913	none	24	Bare — sound only, no I/O ports
YM2149F	A + B	40	Yamaha-made; software-compatible, with a 5-bit envelope generator against General Instrument’s 4-bit — 32 attenuation steps rather than 16

See also

• AY-3-8910
• ZX Spectrum