The Dreamcast connector is a wild, multi-functioned beast. It offers several outputs in the default configuration (Composite and S-Video), and can output two kinds of 15kHz RGB (SCART), as well as 31kHz RGB (VGA) when the proper mode is selected.
|1||Ground||9||Horizontal Sync (for VGA)|
|2||Right Audio||10||Composite Sync|
|3||Left Audio||11||S-Video Chrominance (C)|
|4||+12v||12||S-Video Luminance (Y)|
|6||Mode Select 1||14||Blue Out|
|7||Mode Select 2||15||Green Out|
|8||Vertical Sync (for VGA)||16||Red Out|
The mode select pins are 6 and 7. Ground either one for two kinds of 15kHz RGB (SCART), ground both for 31kHz RGB (VGA). Note that the Dreamcast outputs VGA, the box or cable does not 'upscan', so Dreamcast VGA boxes cannot be used for converting low-res RGB to VGA on other consoles.
You should use a 220uF capacitor on each of the RGB lines (+ towards console).
15kHz/31kHz RGB Note:
If a certain game will not boot in either RGB mode it can sometimes be 'forced' into RGB by fitting a break-before-make switch between ground and one, or both, mode select pins. Once this is done power up the Dreamcast with the switch in the 'standard mode' (Neither pin grounded) and flick the switch after the game disk has already started to be read (When loading original GD-ROM's you will hear a 'beep' sound from the drive at this point) this can often trick incompatible games into the desired mode.
When the mode select pins are used certain signal outputs are enabled or disabled:-
|Pin||Description||Standard 'TV' Mode||15kHz RGB (SCART)||31kHz RGB (VGA)|
|2||Right Audio||Right Audio||Right Audio||Right Audio|
|3||Left Audio||Left Audio||Left Audio||Left Audio|
|6||Mode Select 1||Unused||Unused||Grounded|
|7||Mode Select 2||Unused||Grounded||Grounded|
|11||S-Video Chroma (C)||S-Video Chroma||?||Disabled|
|12||S-Video Luma (Y)||S-Video Luma||?||Disabled|
|13||Composite Video||Composite Video||?||Disabled|
Note:- According to the schematics the HSYNC and VSYNC signals come directly from the 'HOLLY' GPU and are sent to both the DAC/Encoder and the AV port, which means they are likely active in all modes (Even standard 'TV' mode, when no RGB signals are present) However CSYNC is generated by the DAC/Encoder, so is unfortunately only active in specific modes.