MODE 4
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.
| 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) | |
| Screen display MODEs |
|---|
|
MODE 0 | MODE 1 | MODE 2 | MODE 3 | MODE 4 | MODE 5 | MODE 6 | MODE 7 |
-- beardo 14:13, 16 September 2006 (BST)
