In this project, I had a go at generating a grayscale PAL video signal. I used a TI Stellaris Launchpad and made an R2R DAC. There is still some room for improvement, but this is what I've done so far:
Timing: Timing is based on an interrupt which goes off every 64 µs. This marks the start of each line of the image (hsync), or the start of a vsync pulse.
Memory: A 24 KiB array is used as video memory. Only the least significant nibble of each byte is currently being used. One possible future use of the most significant nibble would be to use it for double-buffering of the image.