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Does the Dragon support the "extended" VDP?
Posted: Mon Jul 06, 2009 11:19 pm
by jmk
The CoCo2 (some models) has a later revision of the VDP which supports a few extra text mode trinkets, I was wondering if the Dragon models supported this as well?
Extended CoCo VDP.
$FF22
$80 = Select graphics mode (as usual).
$40 = Extend background colour as border.
$20 = Reverse text.
$10 = Lowercase.
$08 = Second palette (as usual).
Note: extended border remains black when text is reversed.
Re: Does the Dragon support the "extended" VDP?
Posted: Tue Jul 07, 2009 7:40 am
by sixxie
This is the 6847 "T1", which (AIUI) was produced specifically for Tandy by Motorola. I've never seen a Dragon with one. To be honest, although having lower case would be nice, I think the upper case font on the T1 looks worse than the old one (and of course would make any game that used fragments of it in Semigraphics 24 mode look fairly poor).
Re: Does the Dragon support the "extended" VDP?
Posted: Fri Jul 10, 2009 8:21 pm
by JamesD
I think the new version of the 6847 would have required a new board layout. I believe it had a built in latch to capture data on the input lines instead of an external one.
Re: Does the Dragon support the "extended" VDP?
Posted: Sat Jul 11, 2009 9:17 am
by sixxie
Yes, I think possibly all CoCos have this latch anyway, and it stops you using the "hi-res" plus 2-colour block graphics trick.
Actually that's probably the mode you get lower case in
Re: Does the Dragon support the "extended" VDP?
Posted: Wed Jul 15, 2009 3:15 am
by JamesD
All CoCos do have a latch, it's just internal on the newer 6847 vs external on older CoCos.