This is a SN76489-based sound card for the RC2014. It is a very simple chip, only capable of producing square waves and a noise channel, without any envelope control or filters. This chip was used in the TI-99/4A, ColecoVision, Sega SG-1000, Sega Master System, Sega Genesis, IBM PCjr, Tandy 1000, BBC Micro, as well as many arcade games.

The board can optionally support two SN76489 chips for 6 channel stereo sound, but currently this is unsupported by any software. If stereo sound is not desired, then the second chip and its supporting components can be omitted.

Ready-to-Assemble Kits are available on Tindie. These are sold by Michael Kamprath with my permission. However, I offer no warranty or guarantee of support.

Gerbers for the PCB are available. I highly recommend JLCPCB for PCB fabrication. Alternatively, boards can be ordered from the shared project on OSH Park.

Refer to the schematic, the picture below, and the bill of materials below for assembly guidance.

All parts except for the SN76489 are available from Mouser. The SN76489 can be obtained from eBay.

Some components are optional:

*U4, C3, C5, J8 and J9 can be omitted if you do not want stereo sound.

**U3 and C2 can be omitted if you don't need tight address decoding.

The recommended jumper settings select a ColecoVision compatible configuration with the the first chip at address FF and the second chip at address FB. On a real ColecoVision, all ports E0-FF are assigned to the sound chip, but all known games use port FF. Mono output is selected since no available software supports the second chip. To enable output from the second chip, move JP2 to the bottom position (stereo).

• J7 and J9 configure A7-A5 for the left and right chips respectively. From top to bottom, these jumpers select the following address ranges: 00-1F, 20-3F, 40-5F, 60-7F, 80-9F, A0-BF, C0-DF, E0-FF.
• J6 and J8 configure A4-A2 for the left and right chips, respectively. The bottom position selects don't care for A4-A0, so the full range selected by J7 or J9 will be used. Each of the 8 positions above this selects a range of 4 addresses: X0-X3, X4-X7, X8-XB, XC-XF, Y0-Y3, Y4-Y7, Y8-YB, and YC-YF, where X is the lower half and Y is the upper half of the 32-address range selected by J7. J8 has one additional jumper in the topmost position which completely disables the right chip.
• J3 configures A1 for both the left and right chips. It can be configured for 0 (bottom), 1 (middle), or don't care (top).
• JP1 configures A0 for both the left and right chips. It can be configured to 1 (bottom) or don't care (top).
• JP2 selects mono (left) or stereo (right) operation. In mono mode, the left chip is connected to both left and right channels on the audio jack.

• SN76489 Manual
• SN76489 Development
• The Z80 and the SN76489

• TMS9918A Video Card: my TMS9918A video card for the RC2014
• Game Controller Card: my Atari/Sega/Coleco-compatible controller interface board for the RC2014
• z80ctrl: my AVR-based bus monitor and bootloader board for the RC2014

Copyright 2018 J.B. Langston

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