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⌂ ∞ ▽ Elite on the BBC Micro and NES

Version analysis of SETVDU19 / DOVDU19

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

Code variation 1 of 5A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Master
6502SP
       Name: DOVDU19

       Name: SETVDU19

       Type: Subroutine
   Category: Drawing the screen

Code variation 2 of 5A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Master
6502SP
    Summary: Change the mode 1 palette

    Summary: Implement the #SETVDU19 <offset> command (change mode 1 palette)

Code variation 3 of 5A variation in the comments only

This variation is blank in the Master version.

6502SP
 This routine is run when the parasite sends a #SETVDU19 <offset> command.

 This routine updates the VNT3+1 location in the IRQ1 handler to change the
 palette that's applied to the top part of the screen (the four-colour mode 1
 part). The parameter is the offset within the TVT3 palette block of the
 desired palette.



 Arguments:

   A                    The offset within the TVT3 table of palettes:

                          * 0 = Yellow, red, cyan palette (space view)

                          * 16 = Yellow, red, white palette (charts)

                          * 32 = Yellow, white, cyan palette (title screen)

                          * 48 = Yellow, magenta, white palette (trading)

Code variation 4 of 5A variation in the labels only

Tap on a block to expand it, and tap it again to revert.

Master
6502SP
.DOVDU19

.SETVDU19

 STA VNT3+1             \ Store the new colour in VNT3+1, in the IRQ1 routine,
                        \ which modifies which TVT3 palette block gets applied
                        \ to the mode 1 part of the screen

Code variation 5 of 5Related to Elite's use of the Tube

Tap on a block to expand it, and tap it again to revert.

Master
6502SP
 RTS                    \ Return from the subroutine

 JMP PUTBACK            \ Jump to PUTBACK to restore the USOSWRCH handler and
                        \ return from the subroutine using a tail call