[Coco] more overscan antics on the coco II

[Simon Jonassen]

Hi Torsten...

Started experimenting with xroar... Thought it was a glitch....

So i tried it on a real coco... Worked aswell... Not stable first time
around, but i'm getting there....

Real coco needed a little more tweaking.... (nop) etc....

Basically just flip $ff22 all the time as in:

Lda $ff22
Anda #$f0
Sta $ff22
Lda $ff22
Eora #$80
Sta $ff22.......

The eora does the magic....

Needs very carefull timing though...

It works for text/sg/graphics...

/Simon :-)

 

-----Oprindelig meddelelse-----
Fra: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] På
vegne af Torsten Dittel
Sendt: 21. april 2013 22:01
Til: coco at maltedmedia.com
Emne: Re: [Coco] more overscan antics on the coco II

Simon Jonassen <simon at ...> writes:

> Even more twiddling about reveals more posibilities....
> 
> http://roust-it.dk/coco/more_overscan.jpg

Simon, interesting. Did you figure it out on a real CoCo2 system, or is it
just XROAR showing that behaviour? I assume it's a "stable" display you're
showing? Could yo achieve that as well in HiRes Graphics modes?

Did you have a look at http://TRS-80.CC/DRAGFIR2.BIN ? This has some stable
partial border lines painted, some of them even with smooth vertical
animation. Works with XROAR and on 50HZ PAL machines only.

A screenshot here:

http://www.6809.org.uk/tmp/da/pal_coco_probe/pal-dragonfire-1.png

Keep researching! I guess the VDG contains more funny things we don't know
yet (e.g. I never played around with desyncing it using the Hispeed POKE
65497,0 at the right point of time and then POKEing back to slow speed in
the visible area).

Regards, Torsten



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