Re: Double Hi-Res on 128Kb IIe or //c.

[jon@i-manila.com (Jon Co)]

Double high resolution (DHR for short) graphics has only 16 colors
(fixed), no palette of 256 colors to choose from.  This is the same 16
colors of lo-res graphics.  It is the side-effect of the 80 column
circuitry, which needed twice the amount of dots to display 80 column.
 Since it was just a side-effect, this mode wasn't really officially
supported.  In fact the //e extended 80 column cards were configured
at the factory to NOT support DHR graphics.  You have to install a
jumper to connect the 2 molex type pins on the extended 80-column
card.  This was done because early (Rev A) apple //e's do not support
DHR graphics and using a jumpered extended 80 column card on a Rev A
board will cause your //e to not start up.
And besides that, the 65C02 only has a 16 bit address bus, meaning it
can directly access only 64k of memory.  any expansion memory has to
be switched around.  This makes it very hard for the Applesoft
programmer to access DHR graphics, because there are no built in
applesoft commands that work with it, and you cannot readily poke and
peek values from auxillary memory without resorting to machine
language subroutines.
Were there many arcade games that utilized DHR?  I remember only 1
game, airheart (which i never finished).  The rest were adventure
games.
Jeff Thomas <a2forever@usa.net> wrote in message news:<3E37B6C0.52A5E558@usa.net>...
> I was reading in old Apple II oriented magazine that the double high
> resolution (560 x 192 pixels) mode on Apple IIe with 128Kb of RAM or
> //c, could display twice the resolution as 'normal' hi-res in 6 colours.
> While, double hi-res has 16 colours from palette of 256 colours. Is that
> true?
> 
> Seems to me, Apple left a void filled by "Beagle Graphics" and other
> programs to enable access to this graphics mode. Why did Apple make it
> so hard to use it, without thirt-party software?