MODE 8

Demonstration of 'MODE 8' (BBC)

MODE 8 is the unofficial title of an ultra-low resolution screen MODE, a program for which appears on page 383 of The Advanced User Guide for the BBC Microcomputer (Bray et al., 1983?) Another program, attributed to Ian Robertson, was published in The Micro User magazine (November 1985, p.123). It works on the BBC Micro but not the Electron or Master, or the Archimedes (where MODE 8 is officially a 4-colour version of MODE 0).

The MODE 8 code modifies the MODE 5 screen to provide a 80 × 256 display in 16 colours. The MOS does not allow complete support of this MODE and some bugs can be seen: for instance, graphics drawn off the right-hand edge of the screen wrap around to the left, shifted down one text row; and text windows do not work correctly.

'MODE 8'

Type	Graphical ('ASCII')
Resolution	Text	10 × 32 characters
	Graphics	80 × 256 pixels
Character size	8 × 8 pixels, user definable
Pixel aspect	4:1 (wide)
Bits per pixel	4
Default palette	Logical colour	Actual colour
	0	0 (black)
	1	1 (red)
	2	2 (green)
	3	3 (yellow)
	4	4 (blue)
	5	5 (magenta)
	6	6 (cyan)
	7	7 (white)
	8	8 (flashing black/white)
	9	9 (flashing red/cyan)
	10	10 (flashing green/magenta)
	11	11 (flashing yellow/blue)
	12	12 (flashing blue/yellow)
	13	13 (flashing magenta/green)
	14	14 (flashing cyan/red)
	15	15 (flashing white/black)
Memory	allocated	10240 bytes
	on screen	10240 bytes
Address range	Model B etc.	&5800..&7FFF
Configuration	Video ULA control register	&E0
	Video ULA palette register file	&07 &16 &25 &34 &43 &52 &61 &70 &8F &9E &AD &BC &CB &DA &E9 &F8
	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 01:39, 13 December 2006 (GMT)