Texas Instruments SN76489
The SN76489 Digital Complex Sound Generator (DCSG) is a TTL-compatible Programmable Sound Generator chip from Texas Instruments. It contains three square wave tone generators and one white noise generator, each of which can produce sounds at various frequencies and sixteen different volume levels.[1] Its main application has been the generation of music and sound effects in game consoles, arcade games and home computers (such as the BBC Micro and the IBM PCjr), existing alongside the competing and similar General Instrument AY-3-8910
The frequency of the square waves produced at each channel is derived by two factors: the speed of the external clock and a value provided in a control register for that channel (called N). Each channel's frequency is arrived at by dividing the clock by 32 and then dividing the result by N.[1]
Sega used SN76489 clones in their Master System, Game Gear, and Mega Drive/Sega Genesis game consoles. These modified sound chips were incorporated into the system's video display processor. Although basic functionality is almost identical to that of the original sound processors, a few small differences existed: the randomness for the noise channel is generated differently, the "periodic noise" output is a 1/16 duty cycle (as opposed to 1/15 on the original), and the Game Gear's version includes an extension for stereo audio output.[2]
Another clone is the NCR 7496, used in the Tandy 1000 computer. It again has a different white noise pattern but is otherwise functionally identical to the SN76489.[citation needed]
It is worth noting that the SN76489 seems to be totally identical to the SN76494 and SN76496 in terms of the outputs produced, but they additionally feature an "AUDIO IN" pin for integrated audio mixing.[3]
References
- ^ a b Engineering staff of Texas Instruments Semiconductor Group. "SN 76489 AN" (PDF).
- ^
Maxim (April 27, 2005). "SN76489 notes". SMS Power!.
{{cite web}}: External link in|work= - ^
"SN76494, SN76494A, SN76496, SN76496A programmable tone/noise generator" (PDF). Texas Instruments. 1984, 1989.
{{cite web}}: Check date values in:|year=(help)