Dreamcast overscanning

[blackevilweredragon]

I noticed that the DC really outputs 720x480, but games only use 640x480 (thus resulting in a blank overscan area horizontally)..

Is there any way to fix this?  I'm using an old IBM VGA monitor which has NO geomertry controls, and the resulting image is a 5:4 like image, not 4:3..  when the DC boots with it's logo, and the "Produced by.." message, it's a 4:3 image, but as soon as a game starts, you lose the edge and get a skinner image..

EDIT:  Here's a video of what I mean..

http://blackevilweredragon.spymac.com/dcscan.mp4

you can clearly see that it's not a resolution change, but it "fades" into this odd state..

[ken_cinder]

Do you get this with games that are supposed to support VGA? I think the Dreamcast menu isn't geared for VGA, but will display in VGA and suffers from the overscan that non-vga games forced into VGA mode will.
Games that are designed to make use of VGA shouldn't do this.

As for fixing it at the hardware level, not unless you know some magical way, cause I sure don't.

[blackevilweredragon]

every VGA game does this...

even DC linux does it, but shifted more to the left...

[ken_cinder]

That's odd, I had another look at the video and it's displaying like a 1:1 image, perfectly squared.
I'm pretty baffled, my Dreamcast displays fine in VGA mode even on my HDTV, no overscan issues, and I've never seen that happen. Maybe it's a scan rate issue with the monitor?

[blackevilweredragon]

does it on all my monitors...

hook it up to your VGA monitor, and size down the H-Size, boot it up, and you should see the same thing happen...

[blackevilweredragon]

this guys DC has the same smaller H-Size too:  http://www.raphnet.net/electronique/dreamc...reamcast_en.php

of course his monitor could just be set wrong, but his V-Size is perfect, so I doubt it..

[ken_cinder]

Guess it's just something I've never noticed, that is odd. You'd think overscan wouldn't be enabled in VGA mode, only in the 15khz modes which are designed for televisions. And for some reason, even though my Gamecube has overscan issues in 480p on my HDTV, my Dreamcast doesn't via VGA.

I came across a Linux toolset for modifying display settings on monitors without external controls using DDC/CI parameters, I'm not sure if the settings made will stick outside of the running OS when the changes are made, or if it even supports your monitor, but it's on Sourceforge...might want to see if you can find it and see if you can get rid of the overscan using it.

Aha, here it is: http://sourceforge.net/projects/ddccontrol/

[blackevilweredragon]

DC Linux can't change video modes, the VGA BIOS in the DC seems to be fixed..  though, in DC linux, with fbset, i could move the picture left and right, but not correct the size..   So the DC does know it's doing it...

it seems to just be that the output is still running at 720x480 with a 640x480 image on top, and only the Boot logo and TMSS runs at full 720x480..

this monitor is the first VGA monitor (2-row VGA connector), it doesn't have DDC support  it doesn't even have a computer, it's just a dumb CRT device..

[ken_cinder]

I think you're SOL with your only option being adjustments inside the monitor itself (If it's even possible).

[blackevilweredragon]

this monitor review also shows the issue with his DC, he calls it vertical banding..

http://www.bexox.com/showdown.htm

I think the DC's BIOS was designed this way..  while it can change the sync rate, it doesn't change the resolution...  I was wondering that if I played with the h-sync, sizing it could work..

[acem77]

my samsung dlp does the same exact thing when using the vga jack.
i thought it was just my tv till i read this.
my tv will sync at 31khz or 15khz.
by pluging and unpluging the vga box into the dreamcst i can trick the box to output rgb at 15khz.
when this happens the tv will display the signal at a perfect 4:3 ratio.
but i get all the unwanted effects of a 15khz video signal on the vga jack.
i can mess with some aspect settings on the tv when in true vga mode but non make the dreamcast look right.

[NFG]

I put a 15kHz switch on my VGA box.  Works a treat.

[blackevilweredragon]

this monitor don't support 15KHz..  oddly IBM says "35.7KHz and lower", but then again, that was written in the 80's, they probably didn't know any better.