From Sega Retro
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|Designer: Texas Instruments|
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 programmable square wave 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.
- See Sega Master System/Technical specifications for more details
The Sega SN76496, also known as the Sega PSG, is based on the SN76489. A difference is that the SN76496 features an "AUDIO IN" pin (on pin 9) for integrated audio mixing. The Sega PSG is included 'on-chip' in Sega's Video Display Processors (VDP) for their Master System, Game Gear and Mega Drive game consoles. The Master System VDP is in turn based on the Texas Instruments TMS9918A VDC (Video Display Controller) used in the Sega SG-1000.