Using a sync splitter
If your monitor does not support sync on green you need an additional sync splitter. The sync splitter used here is the LM1881N from National Semiconductor (
http://www.national.com/pf/LM/LM1881.html ).
You need to build the same cable as described above. Additionally, build the following circuit:
--> ascii circuit diagram cut out <--
Both methods, pure sync-on-green and sync-splitter, suffer from the fact that the XBox does not deliver VESA compliant sync-on-green signals. The VESA standard requires sync pulses with negative voltage, with the color signal starting at 0 Volt. The XBox, however, cannot produce negativ sync pulses. Instead it uses a positive voltage offset on the green signal with the sync pulses going down to 0 Volt. This may result in a slight colour shift, depending on how well your monitor is able to cope with the voltage offset. Usually dark gray colors will appear slightly green.
One way to solve this problem in hardware is to subtract the sync information from the green signal and deliver the resulting signal to the monitor. Some vendors sell VGA adapters for PS/2 that use this approach, e.g. Blaze (http://www.blaze-gear.com/p2_017.htm). If you replace the PS/2 plug with an XBox AFIP plug the adapter will also work on an XBox.
Another problem is the width of the sync pulses which is fixed by the Conexant mode, i.e. it cannot be modified by software. The higher the pixel clock rate gets the shorter the sync pulses become. It's up to the sync logic in your monitor how well it will cope with the short sync pulses at higher pixclock rates.
, but I'm thinking of going for a 17" screen since I can't seem to find any 15" panels @ 1280x1024. The other option is to go for a 15" LCD TV which would have all sorts of wonderful inputs and upscalers built in. But I digress.
