frequency doubling

Frequency doubling is relatively easy, if you'll accept a pulse on the output for each edge on the input. But that's most definitely not what's needed heer. Much harder is to half the width of each pulse in the input signal, preserving the relative timeings of the 5 signals. And even that's not what uou need here. TO go from CGA to VGA you have to double the horizontal sync freqeucny (and 'speed up' the video signals), but keep the vertical sync frequency unchanged. You therefore double the number of lines in the picture. Essentially what uou have to do is sample the colour signals and read them into a bufffer, then read that buffer out twice as fast -- and twice -- to the monitor. Not too hard, but not a couple of TTL chips either. -tony