SN76489

The SN76489 is a TTL compatible, 4 channel Programmable Sound Generator (PSG) IC from Texas Instruments. Its main application has been entertainment and it has been used to provide music and sound effects in game consoles, arcade hardware and home computers.

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). The eventual frequency is arrived at by dividing the external clock by 32 and then dividing the result by N for each channel. The SN76489 is included 'on-chip' in Sega's Video Display Processors (VDP) for their Master System, Game Gear, and Megadrive game consoles. The Sega VDP is in fact based on the Texas Instruments TMS9918 VDP.