1. Ensure that you are using port 0x08 as the COLOUR PORT.
2. When using the Alpha Plus (Premium Series) and later models, ensure that the APLUS VIDOPTS PORT (port 0x1C) is set correctly.
It's best to learn with the APLUS VIDOPTS PORT disabled with a value of 0x00.
If it's turned on, then video attributes and video memory bank select are in effect so they too must be correctly populated/configured.
The microbee went through 2 colour design iterations:
The first used a 2 bits per colour regime on the output connector with the background colour intensity set via bits 1:3 of the COLOUR PORT.
Allocation of the colour RAM is split [7:5]=Backgnd, [4:0]=Foregnd (i.e. only 32 colours fore gnd available & 8 colours for backgnd with global intensity control)
The COLOUR PORT address as both 0x08 & 0x18.
The second used by the Alpha Plus (Premium Series) and later used 4 bits per colour to confirm with the IBM CGA (i.e. 16 colours for both foregnd and backgnd).
Allocation of the colour is assigned by NYBBLE - Backgnd = MSN, Foregnd = LSN.
The COLOUR PORT address is only 0x08.
Both use bit 6 of the COLOUR PORT to switch in the COLOUR RAM into the memory map.
This is how things can look when properly configured and working.
Beware of the horrible music!
2. When using the Alpha Plus (Premium Series) and later models, ensure that the APLUS VIDOPTS PORT (port 0x1C) is set correctly.
It's best to learn with the APLUS VIDOPTS PORT disabled with a value of 0x00.
If it's turned on, then video attributes and video memory bank select are in effect so they too must be correctly populated/configured.
The microbee went through 2 colour design iterations:
The first used a 2 bits per colour regime on the output connector with the background colour intensity set via bits 1:3 of the COLOUR PORT.
Allocation of the colour RAM is split [7:5]=Backgnd, [4:0]=Foregnd (i.e. only 32 colours fore gnd available & 8 colours for backgnd with global intensity control)
The COLOUR PORT address as both 0x08 & 0x18.
The second used by the Alpha Plus (Premium Series) and later used 4 bits per colour to confirm with the IBM CGA (i.e. 16 colours for both foregnd and backgnd).
Allocation of the colour is assigned by NYBBLE - Backgnd = MSN, Foregnd = LSN.
The COLOUR PORT address is only 0x08.
Both use bit 6 of the COLOUR PORT to switch in the COLOUR RAM into the memory map.
This is how things can look when properly configured and working.
Beware of the horrible music!