Re: Hopefully last dumb newbie question.

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

David Empson <dempson@actrix.gen.nz> wrote:

> You could look at the contents of the shadow register ($C035).  Bit 5 is
> zero if text page 2 shadowing is enabled (on the 1MB/ROM 3 motherboard
> only).
> 
> The catch: this register is fiddled with by the monitor firmware, so you
> can't reliably read it from the command line.

[Remaining details snipped]

For anyone else who was trying out my example code: it doesn't work.  I
was right - the monitor does fiddle with the shadow register, but in
even weirder ways than I anticipated.

The safest way to read the shadow register value without risking it
being fiddled behind your back is to do it with a PEEK in BASIC:

PRINT PEEK(-16331)

On a ROM 3 IIgs, with Alternate Display Mode OFF, the printed value
should be 40 or 32.

With Alternate Display Mode ON, the printed value should be 8 or 0.


Mitchell and I are still experimenting with this, and have yet to come
up with a definite answer on whether his computer behaves any
differently from mine in this area.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand