Re: DHGR Video Riddle Solved!!!

["Arkain" <rwking@no.usa.spam.net>]

Phoenyx <quazar@dcnet2000.com> wrote in message
39C1BFAF.F9363388@dcnet2000.com">news:39C1BFAF.F9363388@dcnet2000.com...
> > If AN3 isn't user accessible, then how does one enable DHGR in software
> > on a IIc? If you can't toggle AN3 in software, then the PAL will
> > continue to force all graphics to be shifted out at 7MHz, i.e. no DHGR.
> > So how exactlly does it work if AN3 isn't user accessible?
>
> AFAIK, it is done in the hardware. I have researched some of this since
> it didn't make sense. Dhires has always been a bit of a mystery to me
> even with all the reading I have done on it. I have a basic understanding
> of how the bitmaps work on the screen, just not at the hardware level.
> IIRC, DHR mode is turned on by the soft switches in the $c000+ area I
> forget the exact switches though.

$C00D ->Turn On 80 Columns
$C050 ->Turn Graphics On
$C057 ->Make It Hires
$C05E ->Turn off AN3

This sequence works on a IIc and a IIe, but if AN3 isn't user accessible
then $C05E, $C05F & $C07F bit7 must all be connected to some other circuit
to enable DHGR mode. If not then IIe DHGR games shouldn't work on a IIc, but
they do.

> I was also under the impression that your method of turning on the DHR
> mode was not sanctioned by Apple Inc due to hardware issues. This may
> also be why the capabilities of an extra screen mode was never mentioned.
> It would not be compatible across the 8 bit systems.

I am left to wonder about that. If the method I'm using wasn't "sanctioned
by Apple" then why did they write a DHGR ampersand driver that they bundled
with the Ex. 80Col. AppleColor card? Why would their manual list an
un-sanctioned method as the "proper way" to enable the various modes?

Seems that the only way to get a clean answer to these questions is to
contact Walt Broedner. If he doesn't remember, then we'll probably be left
guessing about this one.

Arkain