unknown ST Overscan circuit with 7400

[Gunstick]

Hi

I have a self built circuit in my ST for overscan.
I would like to find again how it works. So when I got more infos, I'll add them here.
It uses diodes and some AND gates.
A toggle switch is used to switch the ST into hardware overscan.
The AUTO folder contained software which detects the overscan and initializes GEM with the bigger desktop.
This works in color and mono modes.
The circuit was published in a german ST magazine. I cannot find currently which one.
I wanted to show my botched soldering job, but cannot find an image upload function in the forum. Pics are here: https://twitter.com/inversephase/status ... 2051722241

Georges

[exxos]

This sounds like Lace Scan ? or a variant of. I know some people were talking about the not long ago, but can't remember the conversation. Likely one of these old skool mods.

http://atari4ever.free.fr/#video

[Atarian Computing]

Here is the English manual for OverScan: http://www.atariancomputing.com/downloads/manuals

I built a batch of LaceScans and have sold almost all of them: http://www.atariancomputing.com/blog/ov ... icsupgrade

[exxos]

Here is the English manual for OverScan: http://www.atariancomputing.com/downloads/manuals

I built a batch of LaceScans and have sold almost all of them: http://www.atariancomputing.com/blog/ov ... icsupgrade

Cool stuff

One day this could be something which will be integrated into the new STF logic.

Have you tried running GB6 with the thing running ? Would be interesting to see what happens to the speed of the system overall.

Wasn't the software alternative to this as well though ? I know on my falcon there was various "overscan" PRG's to extend the desktop resolutions, I used to use them a lot. Problem was, the screen area was actually larger than my TV, so the first "inch" of desktop area I couldn't actually see

[Atarian Computing]

Thanks

Good idea on the GB6 bench. I'll have to do that. I get an extended weekend so I'll have time to do it too. Will report back.

Yes, LaceScan's software will work without the hardware even on the STE to give a virtual, extended desktop.

[exxos]

Thanks

Good idea on the GB6 bench. I'll have to do that. I get an extended weekend so I'll have time to do it too. Will report back.

Yes, LaceScan's software will work without the hardware even on the STE to give a virtual, extended desktop.

For use noobs to extra resolutions, if there are software solutions, why is the hardware needed ?

[Atarian Computing]

Thanks

Good idea on the GB6 bench. I'll have to do that. I get an extended weekend so I'll have time to do it too. Will report back.

Yes, LaceScan's software will work without the hardware even on the STE to give a virtual, extended desktop.

For use noobs to extra resolutions, if there are software solutions, why is the hardware needed ?

Software gives you a virtual resolution increase. You still get 640x400 on the screen but your desktop is, say 800x600. The desktop will scroll in different directions as you move the mouse.

LaceScan and others actually increase the displayed resolution. In my LCD I have managed to get 752x480 on the screen.

[tfhh]

Hi,

For use noobs to extra resolutions, if there are software solutions, why is the hardware needed ?

IMHO the hardware is only needed to enable the MMU to scan more than 32000 bytes video memory AND prevent the GLUE vom generating a bus error (2 bombs). I don´t know if we´re talking about the same thing, but the Autoswitch Overscan etablished by a small company in Berlin (Germany) use only one GAL 22V10 and 2-3 discrete parts and wires of course. Rest is realised in software.

[Gunstick]

Apparently the circuit has been published in 68000er may/june 1989
But that hase become ST-Magazin. Were both magazines running in parallel? I don't know.

Unfortunately the archive does not contain the article http://www.stcarchiv.de/stm1989.php
But as I should have the real thing, I will try to find the Magazine and scan it so we all can have a look into the first ever overscan circuit for the Atari ST.

[Atarian Computing]

Here is the GB6 result. Reference is the previous bench I did without LaceScan. Notice the resolutions. Surprisingly there doesn't seem to be a speed penalty. Although unsurprisingly now that you think about it.