TMSdigitizer (for ColecoVision and MSX)
The TMSdigitizer is a small add-on board that can be installed into any machine that uses a TMS9918A/TMS9928A/TMS9929A graphics chip to produce a Lumacode signal. This signal contains all the information of the video screen in a semi-digital form that can be losslessly processed. In conjunction with an RGBtoHDMI upscaler or some other compatible device, this will create a pixel-perfect display.
The mod kit comes with a short length of 2-lead wire and an RCA jack for lumacode output that can be mounted to the case. Because there are many different machines where this mod can be installed in, you will need to use your own judgment how to install the provided parts. There already is a very detailed description from Ian of his installation in a TI99/4a
While it is not possible to give installation instructions for all possible machines (or even all ColecoVision variants), this is how I did the installation in my PAL machine.
In my machine the graphic chip is directly soldered to the board and carries a massive heat sink. Because there is quite some space below the main board, I decided to install the mod board on the underside. To do so, I used individual pins from an precision IC socket to create contacts to the relevant pins in the mod board (which are marked on the underside by white triangles).
Soldering the connector pins to the underside of the main board is quite fiddly, but I succeeded in the end to get good contacts on all of the pins. The lumacode signal goes from the LUM and GND pins to the RCA jack mounted on the case. In my machine there is an unused plastic panel just big enough for three RCA jacks, so this is the perfect place to bring all signals out.
When your machine does not provide a dedicated audio signal besides what is provided in an RF output, you may also want to perform an audio modification. As this is not in the scope of this instruction, I will just show how I arrange the external connectors to provide the following signals:
- Composite video as a fallback option (yellow)
- Audio (red)
- Lumacode (black)
When connecting the new "lumacode" signal to a normal composite or mono video monitor or TV, you will get a grayscale picture where instead of each original pixel, you get two sub-pixels in one of 4 gray levels. I designed the encoding in a way that the average luminance of both sub-pixels roughly resembles the luminance of the original picture.
| first half-pixel | second half-pixel | ColecoVision color | color name | average luminance |
|---|---|---|---|---|
| 0 | 0 | 0 | transparent | 0 |
| 0 | 1 | 4 | dark blue | 0,166666667 |
| 0 | 2 | 8 | medium red | 0,333333333 |
| 0 | 3 | 9 | light red | 0,5 |
| 1 | 0 | 1 | black | 0,166666667 |
| 1 | 1 | 6 | dark red | 0,333333333 |
| 1 | 2 | 5 | light blue | 0,5 |
| 1 | 3 | 7 | cyan | 0,666666667 |
| 2 | 0 | 12 | dark green | 0,333333333 |
| 2 | 1 | 2 | medium green | 0,5 |
| 2 | 2 | 3 | light red | 0,666666667 |
| 2 | 3 | 14 | gray | 0,833333333 |
| 3 | 0 | 13 | magenta | 0,5 |
| 3 | 1 | 10 | dark yellow | 0,666666667 |
| 3 | 2 | 11 | light yellow | 0,833333333 |
| 3 | 3 | 15 | white | 1 |