Dashboard: BULB

       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
 References: This subroutine is called as follows:
             * ECBLB calls BULB


 Arguments:

   A                    The low byte of the address of the character definition
                        of the bulb to be drawn, i.e. #LO(ECBT) for the E.C.M.
                        bulb, or #LO(SPBT) for the space station bulb

   X                    The pixel x-coordinate of the bulb we want to draw


.BULB

 STA P                  ; Store the low byte of the screen address in P

 LDA #HI(SPBT)          ; Set the high byte of P(1 0) to the high byte of SPBT,
 STA P+1                ; so P(1 0) now contains the address of the character
                        ; definition of the bulb to be drawn (this assumes that
                        ; ECBT and SPBT are in the same page and have the same
                        ; high byte)

 LDA #22                ; Set YC = 22, so we draw the bulb on that character row
 STA YC

 JMP letter2            ; Call letter2 to print the character definition pointed
                        ; to by P(1 0) in text column X on character row 22,
                        ; returning from the subroutine using a tail call