Sinclair ZX Spectrum User Manual

Chapter 4
36
Standard / enhanced border
The colour of the border in the standard screen display produced by the Spectrum is
set by writing to output port $FE, and supports just 8 colours. The SPECTRA interface
extends the number of supported border colours to 64 by re-interpreting the byte
written to output port $FE when the standard / enhanced border bit of the display
mode register is set.
In standard border mode, the byte written is interpreted in the usual way as follows:
7
6
5
4
3
2
1
0
Border colour, ordered as GRB
MIC output
Speaker output
Not used
The mode supports just the basic set of 8 colours available from the Spectrum.
In enhanced border mode, it is the state of the basic / extra colours bit in the display
mode register that determines how the byte written to output port $FE is interpreted.
In enhanced border mode using basic colours, the byte written is interpreted as
follows:
7
6
5
4
3
2
1
0
Border colour, ordered as GRB
MIC output
Speaker output
0=Flash with black, 1=Flash with white
1=Bright
1=Flash
The bright bit is used to increase the intensity of the colour specified by bits 0 to 2,
resulting in 16 possible colour values. However, only 15 of these are unique since
black and bright black display the same.
When the flash bit is set, the border colour alternates at a fixed frequency of 1.565 Hz
between the colour specified by bits 0, 1, 2 and 6, and either black (if bit 5 is reset) or
white (if bit 5 is set).

Sinclair ZX Spectrum Specifications

General

Brand	Sinclair
Model	ZX Spectrum
Category	Desktop
Language	English