Texas Instruments SN76489

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Pinout of the standard Texas Instruments SN76489 chip. The packaging is a standard 16-pin DIP. TI SN76489 pinout.svg
Pinout of the standard Texas Instruments SN76489 chip. The packaging is a standard 16-pin DIP .

The SN76489 Digital Complex Sound Generator (DCSG) is a TTL-compatible programmable sound generator chip from Texas Instruments. It contains: [1]

A programmable sound generator, or PSG, is a sound chip that generates sound waves by synthesizing multiple basic waveforms, and often some kind of noise generator and combining and mixing these waveforms into a complex waveform, then shaping the amplitude envelope of the resulting waveform using attack, decay, sustain, and release time periods, so that the resulting waveform then mimics a certain kind of sound.

Texas Instruments American semiconductor designer and manufacturer

Texas Instruments Incorporated (TI) is an American technology company that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globally. Its headquarters are in Dallas, Texas, United States. TI is one of the top-10 semiconductor companies worldwide, based on sales volume. Texas Instruments's focus is on developing analog chips and embedded processors, which account for more than 80% of their revenue. TI also produces TI digital light processing technology and education technology products including calculators, microcontrollers and multi-core processors. To date, TI has more than 45,000 patents worldwide.

Contents

Square wave

A square wave is a non-sinusoidal periodic waveform in which the amplitude alternates at a steady frequency between fixed minimum and maximum values, with the same duration at minimum and maximum. Although not realizable in physical systems, the transition between minimum and maximum is instantaneous for an ideal square wave.

White noise random signal having equal intensity at different frequencies, giving it a constant power spectral density

In signal processing, white noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density. The term is used, with this or similar meanings, in many scientific and technical disciplines, including physics, acoustical engineering, telecommunications, and statistical forecasting. White noise refers to a statistical model for signals and signal sources, rather than to any specific signal. White noise draws its name from white light, although light that appears white generally does not have a flat power spectral density over the visible band.

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, BBC Micro, ColecoVision, and IBM PCjr), competing with the similar General Instrument AY-3-8910.

Arcade game Coin-operated entertainment machine

An arcade game or coin-op game is a coin-operated entertainment machine typically installed in public businesses such as restaurants, bars and amusement arcades. Most arcade games are video games, pinball machines, electro-mechanical games, redemption games or merchandisers. While exact dates are debated, the golden age of arcade video games is usually defined as a period beginning sometime in the late 1970s and ending sometime in the mid-1980s. Excluding a brief resurgence in the early 1990s, the arcade industry subsequently declined in the Western hemisphere as competing home video game consoles such as the Sony PlayStation and Microsoft Xbox increased in their graphics and game-play capability and decreased in cost. The eastern hemisphere retains a strong arcade industry.

Texas Instruments TI-99/4A home computer by Texas Instruments

The Texas Instruments TI-99/4A is a home computer released June 1981 in the United States at a price of US$525. It is an enhanced version of the less successful TI-99/4 model, which was released in late 1979 at a price of US$1,150. Both models include hardware support for sprites and multi-channel sound, some of the first home computers to include such custom coprocessors, alongside the Atari 8-bit family also introduced in 1979. The TI-99/4 and TI-99/4A use the Texas Instruments TMS9900 16-bit processor, making them the first 16-bit home computers.

BBC Micro series of microcomputers

The British Broadcasting Corporation Microcomputer System, or BBC Micro, is a series of microcomputers and associated peripherals designed and built by the Acorn Computer company in the 1980s for the BBC Computer Literacy Project, operated by the British Broadcasting Corporation. Designed with an emphasis on education, it was notable for its ruggedness, expandability, and the quality of its operating system. An accompanying 1982 television series, The Computer Programme, featuring Chris Serle learning to use the machine, was broadcast on BBC2.

Overview

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. [1]

Colorburst

Colorburst is an analog video, composite video signal generated by a video-signal generator used to keep the chrominance subcarrier synchronized in a color television signal. By synchronizing an oscillator with the colorburst at the back porch (beginning) of each scan line, a television receiver is able to restore the suppressed carrier of the chrominance (color) signals, and in turn decode the color information. The most common use of colorburst is to genlock equipment together as a common reference with a vision mixer in a television studio using a multi-camera setup.

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

Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

  1. The speed of the external clock.
  2. 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. [1] 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 (two octaves 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. [1]

Product Family

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. [2]

Texas Instruments SN76489 Product Family Summary
Chip VariantFreq (max)Audio In
TMS9919 / SN94624500 kHzNo
SN76489 / SN76489A4 MHzNo
SN76494 / SN76494A500 kHzYes
SN76496 / SN76496A4 MHzYes

Clones and successors

Sega used real SN76489AN chips in their SG-1000 game console and SC-3000 computer, but used SN76489A clones in their Master System, 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 additional flag register that designates which speaker(s) each audio channel are output (left, right, or both). The periodic noise is also 16 stages long on the Sega-made clones rather than 15; 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. [3]

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.

Usage

Arcade games

Home hardware

See also

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Direct digital synthesis

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References

  1. 1 2 3 4 Engineering staff of Texas Instruments Semiconductor Group. "SN 76489 AN" (PDF).
  2. "SN76494, SN76494A, SN76496, SN76496A programmable tone/noise generator" (PDF). Texas Instruments. 1984, 1989.Check date values in: |year= (help)
  3. Maxim (April 27, 2005). "SN76489 notes". SMS Power!. Archived from the original on May 17, 2006.