MODE 0

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Inter-Word (Computer Concepts, 1986)
Detail from Inter-Word (Computer Concepts, 1986)

MODE 0 is a high-resolution screen MODE, introduced on the BBC Micro Model B and supported by the entire BBC series including the Archimedes. It allows 80 columns of text to be shown but leaves only 9 KB for programs -- even less if a disc interface or Econet is fitted.

MODEs 0 and 3 are the only MODEs to offer 80 text columns. These allow the BBC Micro to work competently as a terminal to mainframes, bulletin boards and the like. Since this was a key requirement in the BBC's specification for a Computer Literacy machine, Acorn developers are said to have worked overnight to get MODE 0 working on the Proton before its demonstration to BBC executives.

As with MODE 3, the bandwidth (pixel rate) is 16 MHz -- too high for the televisions of the day. Characters are recognisable at close range, thanks to Acorn's carefully designed character set, but a monitor is required buying for prolonged use. Compounded by the unusual tall pixels and large memory footprint for a monochrome display, few games have adopted MODE 0 and so it is used mostly for business applications -- word processors and spreadsheets.

MODE 0
Type Graphical ('ASCII')
Resolution Text 80 × 32 characters
Graphics 640 × 256 pixels
Character size 8 × 8 pixels, user definable
Pixel aspect 1:2 (tall)
Bits per pixel 1
Default palette Logical colour Actual colour
0 0 (black)
1 7 (white)
Memory allocated 20480 bytes
on screen 20480 bytes
Address range Model B etc. &3000..&7FFF
Configuration Video ULA control register &9C
Video ULA palette register file &07 &17 &27 &37
&47 &57 &67 &77
&80 &90 &A0 &B0
&C0 &D0 &E0 &F0
CRTC register file &7F &50 &62 &28
&26 &00 &20 &22
&01 &07 &67 &08
(from table in MOS 1.20 at &C46E..&C479)
Screen display MODEs

MODE 0 | MODE 1 | MODE 2 | MODE 3 | MODE 4 | MODE 5 | MODE 6 | MODE 7
MODE 8 | MODE 9 | MODE 10 | MODE 11 | MODE 12 | MODE 13 | MODE 14
MODE &60 | MODE &61 | MODE &62 | MODE &63 | MODE &64 | MODE &65 | MODE &66 | MODE &67
MODE &68 | MODE &69 | MODE &6A | MODE &6B | MODE &6C | MODE &6D | MODE &6E | MODE &6F
MODE | VDU 22

-- beardo 14:09, 16 September 2006 (BST)