SAM Coupé

Palette

Built-in
Submitted by Dan Dooré on Friday, May 25, 2018 - 13:23.
Description

The Coupé’s palette is 128 colours of which 16 can be chosen (MODE1,2&4) or 4 in MODE3 - see Screen Modes.

The default colours are the same as the ZX Spectrum in pot positions 0-7, followed by the same colours again but changed to be equivalent to having the BRIGHT attribute being set.

MODE1 has a ZX Spectrum compatible FLASH feature, BRIGHT is supported via the upper 8 pot positions of the default palette but is transparent to the user when emulating Spectrum behaviour.

The palette can be altered on a per-line basis using the line interrupts in MODEs 2-4 to give multiple colours on screen or to produce effects in the border area on the Splash Screen or see the Fred 41 menu by Matt Round for a simple but effective example.

Complex real-time effects can be seen in more advanced demos such as The Lyra III,  Mnemodemo II or in utilities such as BorderTron 3000.

Instructions

The palette is 7 bits:

Bit Name Description
0 BLU0 least significant bit of blue
1 RED0 least significant bit of red
2 GRN0 least significant bit of green
3 BRIGHT half bit intensity on all colours
4 BLU1 most significant bit of blue
5 RED1 most significant bit of red
6 GRN1 most significant bit of green

 

Trivia

Originally the machine was envisaged to have 256 colours but limited to 64 colours on the development machine due to a shortage of pins on the ASIC that was to be used, see Hardware Bugs but had the extra intensity (BRIGHT) added on Simon Goodwin's suggestion in it's pre-ASIC design stage to give 128.

According to an interview with Bo Jangeborg intervention whilst writing Flash! also upped it to 128:

I convinced them to do away with the hardware flash in the high colour modes. That allowed for a significantly larger pallet. I think it went from 64 to 128 colours. That also allowed me to transfer some pictures from the Atari without too big a degradation.