Product specifications

The mapping arrangement for pattern generator character shapes to the appropriate
colour bytes is shown in the table below.
Pattern Pattern colour Pattern Pattern colour
numbers bytes numbers bytes
0 to 7 0 128 to 135 16
8 to 15 1 136 to 143 17
16 to 23 2 144 to 151 18
24 to 31 3 152 to 159 19
32 to 39 4 160 to 167 20
40 to 47 5 168 to 175 21
48 to 55 6 176 to 183 22
56 to 63 7 184 to 191 23
64 to 71 8 192 to 199 24
72 to 79 9 200 to 207 25
80 to 87 10 208 to 215 26
88 to 95 11 216 to 223 27
96 to 103 12 224 to 231 28
104 to 111 13 232 to 239 29
112 to 119 14 240 to 247 30
120 to 127 15 248 to 255 31
It can be seen that for each block of eight patterns in the pattern generator library the
colour is determined by one byte of the pattern colour cable. This means that to obtain
a wide range of differently coloured graphic patterns in this mode may require some
thought.
Any one of any of the patterns held in the pattern generator library can be displayed in
any position on the current graphics display screen, simply by loading the value of the
desired pattern number into the appropriate position in the graphics display screen
area.
Assuming that we had set up the pattern colour table bytes as below:
Pattern colour table byte 0 = £F1 (Hex), 241 (Decimal)
White on black
byte 1 = £41 (Hex), 65 (Decimal)
Blue on black
The graphics display screen was located at VRAM address £C00 (Hex), 3096
(Decimal) or 3K.
The pattern generator library was located at VRAM address £0 (Hex), 0 (Decimal), or
0K.
Pattern generator table block 0 = Blank pattern
8 = Diamond shape
Then a routine which will blank the screen out and draw a border around the outside
of the screen is listed below. This routine makes full use of the VDP I/O routines listed
in section 1.