The first number after VDU 19 is 0, which normally produces black in mode
128. The second number refers to the actual colour number 1, which always
stands for red. The VDU 19 command effectively changes the association
between the colour numbers and the actual colours:
Colour number assignments Actual colours
in Mode 0 (128) after using
VDU19,0,1,0,0,0
0 Black
0 1 Red
2 Green
3 Yellow
4 Blue
5 Magenta
6 Cyan
1 7 White
8 Black/White
9 Red/Cyan
10 Green/Magenta
11 Yellow/Blue
12 Blue/Yellow
13 Magenta/Green
14 Cyan/Red
15 White/Black
Similarly, white can be changed to yellow by:
VDU 19,1,3,0,0,0
(The last three zeroes are for future expansion and they must be included even
though they have no effect.)
The same principle applies in all other modes except 7 and 135.
The teletext mode
Modes 7 and 135 are unique in the way they display text and graphies.
Commands such as COLOUR, GCOL, MOVE and DRAW do not work in these
modes. Instead, colourful displays are produced using what are known as
teletext control codes.
You may have seen teletext pages broadcast by CEEFAX or Oracle - modes 7
and 135 are teletext compatible modes.
The computer lets you produce your own teletext displays using mode 7 or 135.
These modes use very little memory, and offer a wide range of colours for
simultaneous display on-sereen. The graphics are limited but effective.
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