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⌂ ∞ Elite on the BBC Micro and NES

Drawing the screen: DET1

[Elite-A, I/O processor]

       Name: DET1                                                    [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Show or hide the dashboard (for when we die)

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * tube_table calls DET1




 This routine is run when the parasite sends a write_crtc command. It updates
 the number of text rows shown on the screen, which has the effect of hiding or
 showing the dashboard.

 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.



.DET1

 JSR tube_get           \ Get the number of rows from the parasite into A

 LDX #6                 \ Set X to 6 so we can update 6845 register R6 below

 SEI                    \ Disable interrupts so we can update the 6845

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

 CLI                    \ Re-enable interrupts

 RTS                    \ Return from the subroutine