Version analysis of TRADEMODE - Elite on the BBC Micro and NES

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

6502 Second Processor and Master

Code variations between these versions are shown below.

       Name: TRADEMODE
       Type: Subroutine
   Category: Drawing the screen

Code variation 1 of 5A variation in the comments only

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Master
6502SP
    Summary: Clear the screen and set up a trading screen
    Summary: Clear the screen and set up a printable trading screen

Code variation 2 of 5A variation in the comments only

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Master
6502SP
 Clear the top part of the screen, draw a white border, set the palette for
 trading screens, and set the current view type in QQ11 to A.
 Clear the top part of the screen, draw a white border, set the print flag if
 CTRL is being pressed, set the palette for trading screens, and set the
 current view type in QQ11 to A.



 Arguments:

   A                    The type of the new current view (see QQ11 for a list of
                        view types)

Code variation 3 of 5A variation in the comments only

This variation is blank in the 6502 Second Processor version.

Master
 Other entry points:

   TRADEMODE2           Set the palette for trading screens and switch the
                        current colour to white


.TRADEMODE

Code variation 4 of 5Related to the 6502SP version

The 6502SP version implements printable trade screens by checking whether CTRL is being pressed before displaying the relevant screen.

This variation is blank in the Master version.

6502SP
 PHA                    \ Store the view type on the stack so we can restore it
                        \ after the call to CTRL

 JSR CTRL               \ Scan the keyboard to see if CTRL is currently pressed

 STA printflag          \ Store the result in printflag, which will have bit 7
                        \ set (and will therefore enable printing) if CTRL is
                        \ being pressed

 PLA                    \ Restore the view type from the stack

 JSR TT66               \ Clear the top part of the screen, draw a white border,
                        \ and set the current view type in QQ11 to A

 JSR FLKB               \ Call FLKB to flush the keyboard buffer

Code variation 5 of 5Minor and very low-impact

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Master
6502SP
.TRADEMODE2

 LDA #48                \ Switch to the mode 1 palette for trading screens,
 JSR DOVDU19            \ which is yellow (colour 1), magenta (colour 2) and
                        \ white (colour 3)

 LDA #CYAN              \ Switch to colour 3, which is white in the trade view
 STA COL

 RTS                    \ Return from the subroutine
 LDA #48                \ Send a #SETVDU19 48 command to the I/O processor to
 JSR DOVDU19            \ switch to the mode 1 palette for trading screens,
                        \ which is yellow (colour 1), magenta (colour 2) and
                        \ white (colour 3)

 LDA #CYAN              \ Send a #SETCOL CYAN command to the I/O processor to
 JMP DOCOL              \ switch to colour 3, which is white in the trade view,
                        \ and return from the subroutine using a tail call