The Info List - Texas Instruments SN76489

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The SN76489 Digital Complex Sound Generator (DCSG) is a TTL -compatible programmable sound generator chip from Texas Instruments . It contains:

* 3 square wave tone generators.

* A wide range of frequencies. * 16 different volume levels.

* 1 noise generator.

* 2 types (white noise and periodic). * 3 different frequencies. * 16 different volume levels.

Its main application was the generation of music and sound effects in game consoles , arcade games and home computers (such as the Texas Instruments TI-99/4A , the BBC Micro
BBC Micro
and the IBM PCjr
), existing alongside the competing and similar General Instrument AY-3-8910
General Instrument AY-3-8910


* 1 Overview * 2 Product Family * 3 Clones and Successors

* 4 Usage

* 4.1 Arcade games * 4.2 Home hardware

* 5 See also * 6 References * 7 External links


The SN76489 was originally designed to be used in the TI-99/4 computer, where it was first called the TMS9919 and later SN94624, and had a 500 kHz max clock input rate. Later, when it was sold outside of TI, it was renamed the SN76489, and a divide-by-8 was added to its clock input, increasing the max input clock rate to 4 MHz, to facilitate sharing a crystal for both NTSC colorburst and clocking the sound chip. A version of the chip without the divide-by-8 input was also sold outside of TI as the SN76494, which has a 500 kHz max clock input rate.

TONE GENERATORS: The frequency of the square waves produced by the tone generators on each channel is derived from two factors:

* The speed of the external clock. * A value provided in a control register for that channel (called N).

Each channel's frequency is arrived at by dividing the external clock by 4 (or 32 depending on the chip variant), and then dividing the result by N. Thus the overall divider range is from 4 to 4096 (or 32 to 32768). This gives a frequency range at maximum input clock rate of 122 Hz to 125 kHz (or typically 108 Hz to 111.6 kHz, with an NTSC Colorburst clock input - a range from roughly A2 (A below middle A) to 5-6 times the generally accepted limits of human audio perception).

NOISE GENERATOR: The pseudorandom noise feedback is generated from an XNOR of bits 12 and 13 for feedback, with bit 13 being the noise output. The pseudorandom generator is cleared to 0s (with the feedback bit set to 1) on writes to chip register 6, the noise mode register.


There are two versions of the SN76489: the SN76489 (Narrow DIP version labeled SN76489N) and the SN76489A (Narrow DIP version labeled SN76489AN). The former was made around 1980-1982 and the latter from 1983 onward. They differ in that the output of the SN76489 is the inverse of the expected waveform (the waveform 'grows' towards 0 V from 2.5 V), while the SN76489A the waveform is not inverted.

The SN76496 seems to be totally identical to the SN76489A in terms of the outputs produced, but features an "AUDIO IN" pin (on pin 9) for integrated audio mixing.

Texas Instruments SN76489 Product Family Summary CHIP VARIANT FREQ (MAX) AUDIO IN

TMS9919 / SN94624 500 kHz No

SN76489 / SN76489A 4 MHz No

SN76494 / SN76494A 500 kHz Yes

SN76496 / SN76496A 4 MHz Yes


used real SN76489AN chips in their SG-1000
game console and SC-3000 computer, but used SN76489A clones in their Master System
Master System
, Game Gear
Game Gear
, and 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 SN76489A sound processor, a few small differences existed: the randomness for the noise channel is generated differently, and the Game Gear's version includes an extension for stereo audio output. The periodic noise is also 16 stages long on the Sega-made clones; this makes a significant difference for music/programs which use periodic noise, as sounds will play at 6.25% lower pitch than on the TI-made chips.

Another clone is the NCR 8496, used in some models of the Tandy 1000 computer. Later Tandy 1000 machines (notably the SL, TL and RL series) integrated the SN76496's functionality into the PSSJ ASIC.



* These games shared a common board design by Tehkan that used three of the functionally identical SN76496.

* Baluba-Louk No Densetsu * Senjyo * Star Force
Star Force

* These games shared a common board design by Universal Entertainment Corporation :

* Lady Bug (used 2) * Mr. Do!
Mr. Do!
(used 2) * Mr. Do\'s Castle (used 4) * Mr. Do\'s Wild Ride (used 4) * Do! Run Run (used 4)

* From Konami :

* Road Fighter * Time Pilot \'84 - uses the functionally identical SN76496

* From Sega

* Block Gal * Congo Bongo * Bank Panic * Sega
Mega-Tech * Sega
System 1 * Sega
System 2 * Sega
System E was based on the Master System
Master System
and used the clone chip in its VDP.


* ALF\'s Music Card MC1 - Apple II add-on card, uses three chips for a total of nine voices * BBC Master * BBC Micro
BBC Micro
* Coleco Adam * ColecoVision
* CreatiVision
* Geneve 9640 * IBM PCjr
* Memotech MTX * Neo Geo Pocket
Neo Geo Pocket
* Neo Geo Pocket
Neo Geo Pocket
Color * Game Gear
Game Gear
- used a clone integrated into its VDP; this version has extensions for stereo audio output. * Sega
Genesis * Master System
Master System
- used the clone integrated into its VDP. * Mega-Tech * Pico * SG-1000
- uses the SN76489AN * Sharp MZ-800 - uses the SN76489AN * Sord M5 * Tandy 1000 - early systems used SN76496 or NCR 8496, later systems integrated into PSSJ ASIC * Texas Instruments TI-99/4A - uses the original TMS9919 * Tomy Tutor


* General Instrument AY-3-8910