Texas Instruments SN76489
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The SN76489 Programmable Sound Generator (PSG) is a TTL compatible four-channel sound chip from Texas Instruments. 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).
Features of the SN76489 are:
- Three square wave, programmable tone generators
- One programmable white noise generator
- Programmable attenuation
- Mono audio output
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.
The SN76489 is included 'on-chip' in SEGA's Video Display Processors (VDP) for their Master System, Game Gear, and Megadrive (Sega Genesis in North America), game consoles. The SEGA VDP is in fact based on the Texas Instruments TMS9918 VDP.