Sinclair ZX Spectrum User Manual (English)

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Chapter 4

Half cell

In basic colours mode using single byte colour, the ink colour for the left and right

halves of each cell can be set independently to any of the basic 8 colours. The paper

colour is always black. The format of each attribute cell is as follows:

Right half ink, ordered as GRB

Left half ink, ordered as GRB

1=Bright

1=Flash

The bright bit applies to the full cell and allows a total of 16 different colour values to

be produced, although only 15 of these are unique since black and bright black

display the same. The flash bit applies to the full cell and when set causes the ink

colours to swap over with the paper colour at a fixed frequency of 1.565 Hz.

In basic colours mode using double byte colour, the first attribute cell byte defines the

ink colour for the two halves of the cell and the second attribute cell byte defines the

paper colour for the two halves of the cell. Both bytes are formatted as follows:

Right half colour, ordered as GRB

Left half colour, ordered as GRB

1=Bright

1=Flash

The format encodes the left ink, the right ink, the left paper and the right paper using 3

bits, yielding each a range of 8 colours. Both bytes include a bright bit, allowing a total

of 16 different colour values to be produced for the ink and 16 for the paper, although

in each instance only 15 of these are unique since black and bright black display the

same. The brightness of the left ink and right ink will always be the same, and likewise

the brightness of the left paper and right paper will always be the same.

With the flash bit in both attribute cell bytes set, all ink and paper colours in the cell

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 in the cell 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 in the cell swap between the paper colour and the ink colour.

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General

Processor	Zilog Z80A
Clock Speed	3.5 MHz
RAM	16KB or 48KB
ROM	16KB
Graphics	256 x 192 resolution
Sound	1-channel beeper
Storage	Cassette tape
Input	Keyboard
Power	9V DC
Release Year	1982
Display	TV via RF modulator
Ports	Expansion, RF
Colors	15 (8 colours with two levels of brightness each, plus black)