@emard I have a LCD display with Composite Input. And I tried something similiar
assign vout = active && (xpos == 0 || xpos == 489 || ypos == 0 || ypos == 267); assign sync_ = active || !(hsync || vsync);
I got the knowlege howto handle composite signales from that blog entry https://jeelabs.org/2016/11/composite-video-from-fpga/ and
@lawrie I am still fairly swamped with work stuff. For retro-video my preference normally is to adjust the video circuit to a modern resolution and scan frequency. Often this means doubling the pixel size both horizontally and vertically by repeating a pixel twice in succession (i.e. running the shifter at half the modern pixel speed) and repeating a scan line twice (i.e. skipping the bottom bit of the line number).
That approach does not always work: for example in the ZX80/81 the video signal is largely software generated and there is no actual hardware to tweak. The standard signal could be faked, but a lot of clever software did custom stuff and would hence not work with hardware that emulated the standard software signal. In these cases taking the (often only half-compliant) PAL signal and doing a special converter circuit (either line based or frame based) seems the only way to do it.