MODE 4

From BeebWiki
Revision as of 01:13, 8 March 2015 by WikiSysop (talk | contribs) (1 revision)
Jump to: navigation, search
Starship Command (Acornsoft, 1983)
Vortex (Software Invasion, 1983)
Tomcat (Players, 1989)

MODE 4 is a medium-resolution screen MODE, introduced on the BBC Micro Model A and supported by the entire BBC series including the Archimedes. It allows detailed graphics to be shown while leaving 15 KB or more free for programs; however to achieve this the display is made monochrome.

In Elite and Revs a custom interrupt routine splits the screen in two; the top half is configured as MODE 4 to show the exterior view in detail.

MODE 4
Type Graphical ('ASCII')
Resolution Text 40 × 32 characters
Graphics 320 × 256 pixels
Character size 8 × 8 pixels, user definable
Pixel aspect 1:1 (square)
Bits per pixel 1
Default palette Logical colour Actual colour
0 0 (black)
1 7 (white)
Memory allocated 10240 bytes
on screen 10240 bytes
Address range Model B etc. &5800..&7FFF
Configuration Video ULA control register &88
Video ULA palette register file &07 &17 &27 &37
&47 &57 &67 &77
&80 &90 &A0 &B0
&C0 &D0 &E0 &F0
CRTC register file &3F &28 &31 &24
&26 &00 &20 &22
&01 &07 &67 &08
(from table in MOS 1.20 at &C486..&C491)

-- beardo 14:13, 16 September 2006 (BST)