Date : Mon, 14 May 2007 15:39:16 +0100
From : jgh@... (Jonathan Graham Harston)
Subject: Reduced size modes
>Message-ID: <1179068550.4647288619184@...>
The simplest way to have a display taking up a smaller amount of memory is
to display fewer lines at the bottom of the screen than usual, for
instance only 16 lines instead of 32 lines.
This is simple enough to do on a BBC:
MODE 4 :REM Start with MODE 4
VDU 19,0,4,0,0,0 :REM Set background so we can see effect
VDU 28,0,31,39,16 :REM Define text window
VDU 24,0;0;1279;511; :REM Define graphics window
VDU 23;12,&6C00 DIV &800;0;0;0 :REM Set screen display start to &6C00
VDU 23;13,&6C00 DIV 8;0;0;0
VDU 23;6,16;0;0;0 :REM Set displayed lines to 16
VDU 23;7,27;0;0;0 :REM Set vertical position in centre
HIMEM=&6C00 :REM Set HIMEM to start of new display
You might be able to do the same on the Electron if the MOS translates the
VDU 23 calls appropriately. Otherwise, you have to frobe the hardware with
something like the following:
MODE 4 :REM Start with MODE 4
VDU 19,0,4,0,0,0 :REM Set background so we can see effect
VDU 28,0,31,39,16 :REM Define text window
VDU 24,0;0;1279;511; :REM Define graphics window
?&FE02=&6C00 DIV 2 :REM Set screen display start to &6C00
?&FE03=&6C00 DIV &200
HIMEM=&6C00 :REM Set HIMEM to start of new display
I can't find a way of specifying the height of the display. I think it may
be fixed at 32 or 25 lines according to the mode setting.
> mode with reduced size would be ideal. ISTR that start up for the Electron
> mode 4.
The Electron starts up in whatever mode is specified by OSBYTE 255, which
is reset to &FF on hard reset, so selecting MODE 6 in the absence of MODE
7.
--
J.G.Harston - jgh@... - mdfs.net/User/JGH
The most perfect world is an imperfect world as the imperfections
give people a reason to strive to change it.