Palette



Sam Coupé | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

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

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, see Fred 41 menu for a good example.

Originally the machine was to have 64 colours due to a shortage of pins on the ASIC, see Hardware Bugs and Limitations but intervention by Bo Jangeborg whilst writing Flash! 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.”

see below comment two &three

would the DMA in the MB-02+ - which is only available in real spectrum emulator manage to modify the palette in 2tstates? - roughly?
would this increase the 18 palette changes available when running code in external ram?
if the first three palette changes were not individual palette entries in the clut but were modifications to hmpr bits five and six assuming that you had loaded a 16 colour mode 4 palette in previously -could this affect a mode 3 screen$ - sixteen colours on mode 3 per scan line? - it would be for static screen$ only? far to processor intensive for animations - although the dma could read a full 24576screen$ from an atom lite in 49512 tstates or there abouts?
6mhz dma required?z800 had one built in but was not a feature of the r800 in the msx turboR nor the 24bit address space = 16MB - only need a couple of these bank switched and 2x 1080p screen$ is possible? does other processor range all posses 64k ports? can ram be attached to ports when not paged into processors address space?

Aley
http://www.keprt.cz/progs/ascd/

claims to have communicated with real spectrum bbkrew not sure what language used for programmers mainly grunts n’groans like ghost n’ghoblingoes? impossible to add rzx support to sam also no +D isciple support for ascd? definitely no 8mhzDMA and doesn’t look like either of the two accelerators would have dma

line interrupt

can line interrupt change a palette colour
how many times could this occur on a single scan line please?

Palette change

Yes you can use line interrupt to change palette colour.

After a little test I have found you can change a palette cell up to 9 times in a scan line but only once before your out of border area and the last change will only effect the last few pixels. If you can write code in external memory you can change the colour 3 times in the border area and up 18 times in the line.







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