Date   : Sat, 26 Feb 2005 16:21:14 +0000 (GMT)
From   : "A.Weston" <a.weston2@...>
Subject: Re: Mode 2 text

In <URL:news:local.misc> on Thu 24 Feb, Jonathan Graham Harston wrote:

> I think you mean that there was a weird bug in your programs that
> used VDU 22. If you don't ensure HIMEM is moved below where the
> screen is going to occupy, then BASIC's data will appear in the
> screen. It sounds like you've got the variable heap crawling into
> screen space, like with:
>  
> MODE 7        :REM Select mode 7, reset BASIC's stack to &7C00
> LOMEM=&300    :REM Put BASIC's heap at &3000
> VDU 22,1      :REM Change screen mode to occupy &3000-&7FFF
> fred$="Hello" :REM Add data to BASIC's heap, visible in the screen
>  
> Same thing would happen at the bottom right with data added to
> BASIC's stack:
>  
> PROCfred(x)   :REM parameter pushed onto stack, visible on screen
>
I get a similar effect from the test below although as I say I seem to
remember the garbage appearing at the top left. Maybe not.

MODE7
PROCS
VDU22,1
PROCS
END
DEF PROCS
REM
ENDPROC

AIUI the lookup to the PROCS would now be in the screen memory hence
the blotch.

A.Weston
-- 
Staffordshire, UK of GB&NI. 
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