1.) Square Wave
The SN76489 is a family of PSGs designed by Texas Instruments and released in 1979. Each version of the chip features 3 square wave channels and 1 noise channel. Each channel's volume can be set from 0 to 15. The noise channel can be put into either periodic noise or white noise mode. This was a significant improvement on their earlier chip, the SN76477 and gave rise to copycats emulating TI's 3 Voice Chipset. These improvements made the SN76489 series widely popular throughout the 1980s, even seeing use in home video game systems all the way up until the turn of the century, but it couldn't overtake the AY-3-8910 which dominated the audio chip market at the time.
Minor additions were made to each model in the family, but each is backward compatible to the previous models.
Original is SN76489, narrow version is SN76489N, revised is SN76489A, revised narrow is SN76489AN. This is the most common variation of the chip.
Original is SN76494, narrow version is SN76494N, revised is SN76494A, revised narrow is SN76494AN. Unlike the SN76889, which doesn't use pin 9, the SN76494 utilizes the pin for audio input.
Original is SN76496, narrow version is SN76496N, revised is SN76496A, revised narrow is SN76496AN. Like the SN76494, pin 9 is used for audio input.
With the release of the Sega Master System, Sega acquired the design for the chip and commissioned Yamaha to integrate the PSG inside of their VDP chips. While mostly identical to the original TI SN76489 design, the SEGA PSG expands the noise from 15-bit length to 16-bit length, and modifies the noise's generation methods as well. As such, there is a small software incompatibility when playing SG-1000 games on a Master System.
While the VDP received a massive overhaul for the release of the Sega Genesis in 1990, the PSG core was left untouched, instead being paired with an external YM2612 (OPN2). Later in the Genesis' lifespan, a derivative of the YM3438 was integrated alongside the PSG into the VDP.
A secondary clone of the VDP was made for the Game Gear. While closer in overall functionality to its Master System counterpart, the PSG core was modified to accommodate stereo audio, at the cost of Game Gear music not being directly backwards compatible with the SMS or Genesis VDP clones or the original SN76489.
With the release of the Sega Pico, Sega cut down their Mega Drive hardware, removing the Z80 coprocessor and the YM2612, but the VDP-based PSG made one final hurrah for the entire SN76489 line, being produced and used alongside an ADPCM chip until 2006.
Over the years, a number of computers, video game consoles, and peripheral devices used the SN76496. This is a chronological breakdown of those devices.
|Unreleased (c. 1983)||TI 99/8||SN76494N x1|
|1984-03-??||PCjr 3 Voice||SN76496N x1|
|1984-11-??||Tandy 3 Voice||?|
|1986-06-??||Master System||VDP-based SEGA PSG|
|1988-10-29||Mega Drive/Genesis||VDP-based SEGA PSG|
|1993-06-26||Pico||VDP-based SEGA PSG|
|1995-10-??||Nomad||VDP-based SEGA PSG|
|1998-10-28||Neo Geo Pocket||?|
|1999-03-16||Neo Geo Pocket Color||T6W28 SN76489-like clone|
The SN76489 series didn't see the popularity of its competitor, the AY-3-8910, but it did see a lot of use in the early 1980s.
According to the MAME arcade database, the first time a SN76489 chip appeared on an arcade game was 1980 on Space Force. However, this may be a mistake since it sites the use of three SN76496 chips, but it is unlikely that these particular chips were manufactured until around 1983.
There was an increase in the usage of the SN76489 in 1982 to close to 10 different cabinets, and the chip overtook the older SN76477 model. However, Texas Instruments wasn't even making a dent in the AY-3-8910 market which had about 10 times the popularity.
|SN76489AN Manual||Download - (info)|
|SN76494 / SN76496 Manual||Download - (info)|
Due to the chip's popularity, it has been emulated several times.
- DOSBox emulates it for PCjr and Tandy support.
- MAME has emulated it for the various arcade games that require it.
- Any console or computer emulator in the list of devices above that has music must emulate some version of the SN76489.