70 FOR %a=6144 TO 6144+767
 80 BANK 5 POKE
    %a,INT((RND*1)+0.2)*128 +
    %RND(128)
 90 NEXT %a
100 LAYER 1,3
110 FOR %x=8192 TO 8192+6143
120 BANK 5 POKE
    %x,INT((RND*1)+0.2)*128
    + %RND(128)
130 NEXT %x
140 LAYER 1,1
150 PAUSE 0

Lines 20 and 30 clear the DISP_FILE1 and DISP_FILE2 memory, Lines 70 to 90 fill the COL_FILE1 area with random colour information. The LAYER 1,3 command in Line 100 switches to HiColour mode and subsequently random colour information is written in each attribute cell with lines 110 to 130. As you can see, attribute cells in HiColour mode are much smaller in size and written in an interleaved manner as opposed to the linear manner demonstrated by lines 70 to 90. Finally line 140 switches back to Layer 1,1. To increase the variety of colour combinations and reduce the times of flashing being introduced the FLASH bit is randomised independently.

Extended colour attribute display

The creation of the ZX Spectrum Next brought forth Layer 2 and its extended resolutions and colours. However the need for colourisation of older software arose. What could be done to give a part of the new features to older software without breaking compatibility or having to rewrite from scratch? There have been many solutions offered since the inception of the original ZX Spectrum, each with its own strengths and drawbacks but all had been difficult, and most non-accessible in a straight forward manner from BASIC. A solution in the form of an EnhancedULA was conceived therefore that would give access to the entirety of the ZX Spectrum Next's colour capability without sacrificing compatibility or ease of use.

This is achieved by retaining the DISPLAY_FILE and COLOUR_FILE memory areas but rearranging COLOUR_FILE byte organisation by repurposing the FLASH and BRIGHT bits and increasing the amount of INK and PAPER bits which become pointers to palette colours (see the following sections for more information on palettes). This way, simple commands allow recolouring of older software which is not aware of the ZX Spectrum Next's colour 'abilities' without sacrificing compatibility. Colour clash remains (as do the attribute cell sizes) however the colour capabilities extend to a maximum of 256 colours out of the 512 the ZX Spectrum Next can display. To demonstrate (without getting into too much detail) how you can use more colours using the Extended colour attributes display of the EnhancedULA type the following program:

10 BANK NEW ba
20 FOR %a=0 TO 255
30 BANK ba POKE %a,%a
40 NEXT %a
50 LAYER 1,1
60 PALETTE DIM 8
70 LAYER PALETTE 0 BANK ba, 0