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⌂ ∞ ▽ Elite on the BBC Micro and NES

Dashboard: BULB

[BBC Micro disc version, Docked]

       Name: BULB                                                    [Show more]
       Type: Subroutine
   Category: Dashboard
    Summary: Draw an indicator bulb on the dashboard

    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: No direct references to this subroutine in this source file




 Arguments:

   A                    The y-coordinate of the bulb as a low-byte screen
                        address offset within screen page &7D (as both bulbs
                        are on this character row in the dashboard)

   (Y X)                The address of the character definition of the bulb to
                        be drawn (i.e. ECBT for the E.C.M. bulb, or SPBT for the
                        space station bulb)



 Other entry points:

   BULB-2               Set the Y screen address



.BULB

 STA SC                 \ Store the low byte of the screen address in SC

 STX P+1                \ Set P(2 1) = (Y X)
 STY P+2

 LDA #&7D               \ Set A to the high byte of the screen address, which is
                        \ &7D as the bulbs are both in the character row from
                        \ &7D00 to &7DFF

 JMP RREN               \ Call RREN to print the character definition pointed to
                        \ by P(2 1) at the screen address pointed to by (A SC),
                        \ returning from the subroutine using a tail call