How to generate a 320x200 VGA signal?

Hi. I'd like to build an 80s-style display controller, but I want to output the image to a VGA monitor.

I've seen references to a 320x200 "doublescan" mode, and an XFree86 config file that specifies the timings as:

15.75MHz horizontal, 37.9kHz vertical. 85.3Hz. H: 320 336 368 416 / V: 200 200 202 222

I believe the numbers mean: 320 pixel Video. (336 - 320) = 16 pixel R.Border + F.Porch. (368 - 336) = 32 pixel H.Sync. (416 - 368) = 48 pixel B.Porch + L.Border.

200 line Video. (200 - 200) = 0 line B.Border + F.Porch. (202 - 200) = 2 line V.Sync. (222 - 202) = 20 line B.Porch + T.Border

I have a couple of questions:

  1. 416 x 202 x 85.3 = 1/2 15.75MHz specified, so I'd like to know how the doublescan mode works.

Is it an interlace mode? If so how do you wiggle the VGA connector pins to signal odd/even frames?

Or is it really a 320x400 mode, with every line output twice?

  1. The vertical timing suggets a zero Bottom Border and Front Porch. Is that right? Does the V.Sync come immediately after the last video line?

  1. Ideally what I would like is 320x200 @ 60Hz (or 320x400 @ 60Hz if that's how doublescan works). Can anyone suggest the video timings for that?

Thanks, Paul.

Reply to
Paul Marciano
Loading thread data ...


Take a look at the VGA controller at

formatting link

Regards, rudi ======================================================== ::: Solutions for your ASIC/FPGA needs ::: ..............::: FPGAs * Full Custom ICs * IP Cores ::: FREE IP Cores ->

formatting link

Reply to
Rudolf Usselmann

Here's a design using 640x480 VGA.

formatting link

Reply to
Jean Nicolle

Here are a couple of interesting options:

formatting link

formatting link

The second link is to a page in Japanese, so you'll need to hunt around for the links on it to the actual source files. The cool thing about it is that it appears to be a recreation of the TI TMS9918A video display controller that was used in a number of 80's computers and videogames.


Reply to
Ed Anuff

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.