Sinclair ZX Spectrum User Manual

Chapter 4
33
which cells contain walls and of what type. If these bits are not used by a program
then it is recommended that they always be set to 0.
In extra colours mode using single byte colour, each attribute cell is formatted as
follows:
7
6
5
4
3
2
1
0
Blue (ink), ordered as B
1
B
0
Red (ink), ordered as R
1
R
0
Green (ink), ordered as G
1
G
0
0=Black paper, 1=White paper
1=Flash
The format supports 64 ink colours but only 2 paper colours (black and white). When
the flash bit is set, the ink and paper colours swap at a fixed frequency of 1.565 Hz.
In extra colours mode using double byte colour, the first attribute cell byte specifies the
ink colour and the second attribute cell byte defines the paper colour. Both bytes are
formatted as follows:
7
6
5
4
3
2
1
0
Blue, ordered as B
1
B
0
Red, ordered as R
1
R
0
Green, ordered as G
1
G
0
Unused (available for program use)
1=Flash
The format supports 64 colours for the ink and 64 colours for the paper, resulting in a
total of 64 x 64 = 4096 different combinations. When the flash bits are taken into
account, the number of combinations rises to 4096 x 2 x 2 = 16384.
With the flash bit in both attribute cell bytes set, the ink and paper colours swap over
at a fixed frequency of 1.565 Hz. However, if only the ink attribute byte’s flash bit is set
then just the ink coloured pixels swap between the ink colour and the paper colour,
and if only the paper attribute byte’s flash bit is set then just the paper colour pixels
swap between the paper colour and the ink colour.
Note that the unused bit of each attribute byte is available for use as storage by a
program. It is recommended that these bits are always be set to 0 if not used.

Sinclair ZX Spectrum Specifications

General

Brand	Sinclair
Model	ZX Spectrum
Category	Desktop
Language	English