RGB to SCART for C128

[rkindig]

Hi, all.  I want to get the best video I can out of the C128.  I have a SCART to HDMI upscaler that works so great for the many different machines I've used it for (Atari ST, Amiga, Amstrad CPC, Sinclair ZX Spectrum (+2A), Oric Atmos, BBC Micro, Atari 800XL with Sophia) that have RGB out and want to do the same with the C128.

 

Has anyone used the following cables and/or can tell me if these will or won't work?  And why are there 2 different ones?

https://www.ebay.com/itm/Commodore-C128-C128D-Kabel-an-SCART-40-80-Zeichen-2-0-Meter/361509837112 

https://www.ebay.com/itm/Commodore-C128-C128D-an-TV-Scart-80-Z-Color-mit-Ton-3-Meter/361509837110 

 

thanks!

[carlsson]

A few notes:

 

The C64 mode uses the 5 or 8-pin DIN connector and can only output composite (5 pin) or S-Video (8-pin) at best.

The C128 mode uses both the 5/8-pin connector for 40 column mode and the DE9 connector for 80 column mode.

 

The DE9 connector has pins for RGBI (digital TTL level RGB, similar to CGA) and one pin for monochrome 0.7 Vpp video. In order to use the RGBI on a SCART enabled TV or other device, you need a method to bring down the voltages from ~3V or whatever to 0.7V. The simple circuits do this with using resistors as voltage dividers, some more advanced designs use other type of circuits that may offer additional compatibility or are more "correct" - in the land of electronics there are at least a half dozen solutions to each problem and from time to time lots of arguments which method is the better.

 

The first cable you linked to offers composite video for 40 column mode (due to it only has a 5-pin DIN) and monochrome for 80 column mode.

 

The second cable has a 8-pin DIN, but it doesn't say if it implements S-Video. It also promises colour on 80 column mode, which must mean it has a voltage divider somewhere in the DE9 or SCART side.

 

However here is another gotcha: Despite the SCART connector has 21 pins, it is not enough to have separate pins for composite video, S-Video and all the pins required for RGB since you need those valuable pins for remote controlling your VCR and all the other... (irony). This has the practical limitation that at least one of the pins is shared between RGB and S-Video mode, and your TV needs to be configured to accept either a RGB or S-Video signal. The same would be true about your HDMI upscaler, though I don't know which input signals it accepts in the first place.

 

Technically, the C128 will output a video signal on both the 8-pin DIN and the DE9 at the same time, though you can through the keyboard and in software dictate which video signal system output should go to. In other words, you can have both a 40 column and a 80 column monitor attached at the same time and through advanced software get action on both. While you may not plan to do this, it means the VIC-II chip will output a chroma + luma (S-Video) signal at the same time the VDC outputs a RGBI signal, which the second cable may mix together in the SCART end on the same pin... ????? unless there is another mechanical switch on the cable that prevents one signal from reaching the SCART plug.

 

In any case, for 40 column use (C64) you can never get RGB out of the C128 unless you dig deeper and look for an internal modification which I believe either exists or is under development. It probably involves replacing the VIC-II chip though, or at least put another chip inbetween.

[Laner]

Here's what you want:  https://www.pyrofersprojects.com/blog/product/c128-video-mux/  Handles both 40 and 80 column modes.

 

They're currently sold out, but more are being assembled. 

 

I have one and it works great - I go from the Video Mux SCART out -> BNC -> PVM - however, the S-Video out looks really good as well.