How to generate a 320x200 VGA signal?

[Paul Marciano]

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?

2. 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?

3. 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.

 

[Rudolf Usselmann]

Paul Marciano wrote:

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

[SNIP]

Thanks,
Paul.

Take a look at the VGA controller at www.opencores.org.

Regards,
rudi
========================================================
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[Jean Nicolle]

Here's a design using 640x480 VGA.
http://www.fpga4fun.com/PongGame.html

 

[Ed Anuff]

pm940@yahoo.com (Paul Marciano) wrote in message news:<d5bc3deb.0405251248.38717f73@posting.google.com>...

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

Here are a couple of interesting options:

http://elm-chan.org/works/crtc/report.html

http://www.ohnaka.jp/wiki/wiki.cgi?page=%BB%F7%C8%F3VDP

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.

Ed