VGA output

By popular demand (OK, a couple of people enquired:) the V5Z80P now has VGA output. I’d included digital H/V sync lines on the 8-pin mini DIN socket in anticipation but hadn’t looked into 60Hz VGA video timing until now. Its meant a bit of work on the scanline buffer system, but as this area was something that hasnt changed since the V4 system, it was a good opportunity to tidy up the logic there.

VGA demands a ~31KHz horizontal sync, and line doubling to maintain a lo-res (320×240*) display. I wasn’t sure how stretched the pixels would look, but as you can see by the pictures (TV at the top, PC monitor below) it isn’t too bad.. I’ve just added automatic centring so the video window settings from the usual PAL mode also centre the display on VGA (and realized I now have to auto-offset the scanline-based interrupts too..)

I guess NTSC mode is a possibility, especially as it has much the same overall timing as VGA, something to look into later I think…

(* The display can actually be much wider than 320 pixels).