whitney@think.COM (David Whitney) (08/25/87)
I noticed what seems to be a bug in the video generator. Before any of
you say "oh, he has one of those bad VGCs", my VGC is "good" according
to the serial # on my GS and the # on the VGC itself. So...
Boot up the GS system disk, and in a few moments you have the nice blue
screen of the Launcher. Go into the control panel and set the DISPLAY to
MONCHROME. This should make the output strictly black-and-white. Upon
returning to the Launcher, we see that the screen is still a nice blue.
Gosh.
Launch "DESKTOP.SYS16" to go to the Apple // DeskTop. It's gray. bring up the
control anel and change the display back to COLOR. Upon returning to the
desktop, we see YUCK! all colors and very hard to read. Change it back to
monochrome. That's better.
Upon close inspection of the file DESKTOP1, I see that it does the following:
LDA $C052
LDA $C057
LDA $C050
LDA $C00D
LDA $C00D
LDA $C05E
LDA $C05E
LDA $C051
here are also a couple of manipulations with $C029, which according to
"The Apple //GS Technical Reference" (McGraw/Hill) sets the bit to make output
monochrome (same effect as setting it non-permanently in the control panel).
$C00D engages the 80-col hardware, and referencing it twice (either by 2 reads
or 1 write) actually fully engages the hardware making the screen 80 cols wide.
$C05E makes hires display double-hires. After some poking around, I've come to
the conclusion:
The monochrome setting only takes effect on the hires or double hires
screen after the 80col & double-hires hardware are partially (1 ref) or fully
(2 refs) engaged. Note that double-hires won't be displayed as such unless the
screen is fully engaged to 80 cols. The monochrome setting has no effect on
the super hires screen at all.
Whether or not this is a bug or a feature, I also have a bug for you all.
get yourself into BASIC and type HGR. Type:
HCOLOR=5
HPLOT 0,0
CALL 62454
You are now looking at an orange screen. type CALL-151. At the '*' prompt,
type 'C00D C05E'. OOH! it just turned GREEN! Now type 'C029:21'. Now it's a
bunch of vertical white lines (it turned black-and-white). Type 'C029:1' and
it's green again. type 'C00E C05F' and it's orange again.
Well, there you have it. If your machine DOESN'T do this, I'd like to know.
If people have been able to use the MONOCHROME/COLOR setting in the control
panel without any trouble, I'd like to know. I intend to get my ROMs upgraded,
and I don't need a VGC because of my serial #. I think I do.
David Whitney, MIT '90 Still learning about my Apple //GS
{the known universe}!ihnp4!think!whitney and all of its secrets. Any and all
whitney@think.com technical info appreciated.
DISCLAIMER: You didn't actually believe all that, did you?