Sinclair ZX Spectrum User Manual

Chapter 4
32
Full cell
In basic colours mode using single byte colour, each attribute cell is formatted in the
standard Spectrum manner as follows:
7
6
5
4
3
2
1
0
Ink, ordered as GRB
Paper, ordered as GRB
1=Bright
1=Flash
The ink bits define the colour used for those pixels that are set in the display file, and
the paper bits define the colour used for those pixels that are reset. Both values are
composed of 3 bits, yielding a range of 8 colours for each. When coupled with the
bright bit a total of 16 different colour values are produced, although only 15 of these
are unique since black and bright black display the same. When the flash bit is set, the
paper and ink colours swap over at a fixed frequency of 1.565 Hz.
In basic colours mode using double byte colour, the first attribute byte defines the ink
colour and the second attribute byte defines the paper colour. Both bytes are
formatted as follows:
7
6
5
4
3
2
1
0
Colour, ordered as GRB
Unused (available for program use)
1=Bright
1=Flash
The format encodes the ink and paper using 3 bits each, yielding both a range of 8
colours. The bright bit in each byte extends these totals to 16 different colour values,
although only 15 of these are unique since black and bright black display the same.
With the flash bit in both attribute bytes set, the ink and paper colours swap over at a
fixed frequency of 1.565 Hz and replicate the flash mode of the standard Spectrum
display. 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 bits of each colour byte are available for use as storage by a
program. They could, for example, be used in a maze game to hold flags that indicate

Sinclair ZX Spectrum Specifications

General

Brand	Sinclair
Model	ZX Spectrum
Category	Desktop
Language	English