Re: Can the IIgs output colour on its composite monitor output?

[dempson@actrix.gen.nz (David Empson)]

ralmin <xbiber@bigpond.net.au> wrote:

> David Empson wrote:
> > - If displaying a text-only screen, the IIgs always displays monochrome
> > on the composite output.  You must be displaying a graphics mode
> > (lo-res, hi-res or super hi-res) to get any colour.  (Split screen
> > lo-res or hi-res with four lines of text will have coloured text on the
> > composite output, assuming colour output is enabled.)
> 
> When in GR or HGR mode I get a blue border, blue background on the four
> lines of text, but black background in the graphics area.
> 
> How can I change the background or border colour from Applesoft?

You can change all of the border, background and text colours in the
Display page of the control panel, of course.

Changing the current background and text colour from Applesoft is
reasonably easy: they are stored in a single I/O location, so you can do
a POKE to set them.  (You should PEEK the old value so you can restore
it afterwards.)

The border colour is a little tricky, because its I/O location is shared
with some unrelated items.

Location $C022 holds the text colour (bits 7-4) and background colour
(bits 3-0).  You can set white on black by poking 49816 with 240.

Location $C034 holds the border colour (bits 3-0) and unrelated items in
bits 7-4.  To set the border colour, you must use a read-modify-write
sequence, e.g.

10 P = PEEK(49204)
20 T = 16 * INT(P / 16): REM top bits
30 OB = P - T: REM Old border colour
40 POKE 49204, T + X: REM where X is the desired border colour

To restore the original border colour later, you should repeat this
sequence, i.e. fetch the appropriate value for T again - don't hold onto
the original value.

Note that all of these changes will be lost if you go into the control
panel, as it will restore the system settings.

Changing the system settings is not possible directly from Applesoft,
but may be feasible from a poked-in machine code program.  I don't
recall offhand whether there is any official method of doing this - I
suspect not.