VGA/XGA Timing Diagrams

Gary Preston

Hey all, I've been reading through the 512x384 VGA Driver yesterday and have a question about the timing figures. I'm trying to understand the various timing parameters in the top CON block and although I understand what they represent, eg front porch, back porch, sync, active video etc I'm at a loss for how they were derived.

For example, why 35MHz? Is it as simple as it's running at half the real frequency to allow every pixel clock to really output 2 duplicate pixels effectivly scaling the resolution from 512x384 to 1024x768?

I'd really appreciate a chart/diagram that shows the hsync, front/back porch, active video for horizontal and vertical timing in us and ms if anyone has one or knows of one online.

Forrest

There's info in the Hydra book - see the Chapter 16 sample here www.parallax.com/detail.asp?product_id=70360

Gary Preston

I have the Hydra book and have read the VGA section, but the timing provided is for 640x480 resolution. I'm assuming the HSync and front/back porches will be different for an XGA signal at 1024x768?