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⌂ ∞ Elite on the BBC Micro and NES

Version analysis of DET1 / DODIALS

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 6A variation in the comments only

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

Cassette, Flight, Docked, Master
6502SP
       Name: DET1
       Type: Subroutine
   Category: Drawing the screen
    Summary: Show or hide the dashboard (for when we die)

       Name: DODIALS
       Type: Subroutine
   Category: Drawing the screen
    Summary: Implement the #DODIALS <rows> command (show or hide the dashboard)

Code variation 2 of 6A variation in the comments only

Cassette, Flight, Docked, 6502SP, Master
 This routine sets the screen to show the number of text rows given in X.


 It is used when we are killed, as reducing the number of rows from the usual
 31 to 24 has the effect of hiding the dashboard, leaving a monochrome image
 of ship debris and explosion clouds. Increasing the rows back up to 31 makes
 the dashboard reappear, as the dashboard's screen memory doesn't get touched
 by this process.

Code variation 3 of 6A variation in the comments only

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

Cassette, Flight, Docked, Master
6502SP
 Arguments:

   X                    The number of text rows to display on the screen (24
                        will hide the dashboard, 31 will make it reappear)


 Returns:

   A                    A is set to 6

 Arguments:

   A                    The number of text rows to display on the screen (24
                        will hide the dashboard, 31 will make it reappear)


 Returns:

   A                    A is set to 6

Code variation 4 of 6A variation in the labels only

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

Cassette, Flight, Docked, Master
6502SP
.DET1

.DODIALS

Code variation 5 of 6Specific to an individual platform

This variation is blank in the Cassette, Disc (flight), Disc (docked) and Master versions.

6502SP
 TAX                    \ Copy the number of rows to display into X

 LDA #6                 \ Set A to 6 so we can update 6845 register R6 below

 SEI                    \ Disable interrupts so we can update the 6845

 STA VIA+&00            \ Set 6845 register R6 to the value in X. Register R6
 STX VIA+&01            \ is the "vertical displayed" register, which sets the
                        \ number of rows shown on the screen

 CLI                    \ Re-enable interrupts

Code variation 6 of 6Related to Elite's use of the Tube

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

Cassette, Flight, Docked, 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