Upon reading some of the threads about shifted picture and other sync issues when performing RGB mods on certain systems, a thought popped into my head. Would it be possible to bypass the sync generated by the console and instead use an externally generated sync signal? The generating sync pulses part really doesn't seem too hard to me, its the making sure that it is spitting out those pulses at the correct time during the video signal output that I don't seem to get. Can anyone tell me why this is or is not possible? Part of the reason I am curious about this is for consistency, and to consolize an original GameBoy (Yes I've heard of WideBoy, Super GameBoy, GameBoy Player etc.)
The short answer is no - the slightly longer explanation is that an analog video signal is serial; it starts from the top left corner of the screen, scans across to the top right corner and then moves down the screen scanning each line. The purpose of the sync signals is to tell the display where the frame and each line starts. If you attempt to use some other source of sync signals then you will end up with an image that's randomly positioned on the screen or rolling. This is why you have to use the same source for sync signals as the rest of the video signal (and, on a more general level, why they bother with sync signals in the first place). As for converting the output from something like a Game Boy, there are two basic problems - one is that the overall frame format doesn't fit in with what a TV expects (wrong number of lines) and the other is that it doesn't have "dead time" in the correct places - in an analog video signal there is a period of time between the end of one video line and the start of the next where you put the sync pulse (and blanking time so that the old tube TVs could retrace the beam to the left side of the screen), and a system that's directly driving an LCD doesn't need to wait for this - in most cases they can just send the first pixel of line n+1 immediately after the last pixel of line n. If you want to make a TV-out for something like a Game Boy, you need to grab the pixel data and store it in a frame buffer, then upsample it to the correct resolution for the display, then clock it out with the correct sync signals inserted. In the case of something like the Wide Boy, the first part is being done by the cartridge and the second by the N64 video circuits. There are also many more details I've just ignored for this description (like interlacing and color encoding), but this should give you a general idea.
