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⌂ ∞ ▽ Elite on the 6502

Drawing the screen: DOVDU19

[6502 Second Processor version]

       Name: DOVDU19                                                 [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Change the mode 1 palette by sending a #SETVDU19 command to the
             I/O processor

    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * DEMON calls DOVDU19
             * HALL calls DOVDU19
             * LOOK1 calls DOVDU19
             * TITLE calls DOVDU19
             * TRADEMODE calls DOVDU19
             * TT22 calls DOVDU19
             * TT23 calls DOVDU19
             * WHITETEXT calls DOVDU19




 Arguments:

   A                    The offset of the palette to set



.DOVDU19

 PHA                    \ Store A, the palette offset, on the stack

 LDA #SETVDU19          \ Set A to #SETVDU19, ready to write to the I/O
                        \ processor

 BNE label              \ Jump to label to write #SETVDU19 <offset> to the I/O
                        \ processor, returning from the subroutine using a tail
                        \ call (this BNE is effectively a JMP as A is never
                        \ zero)