Universe: ping

       Name: ping                                                    [Show more]
       Type: Subroutine
   Category: Universe
    Summary: Set the selected system to the current system
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * ESCAPE calls ping
             * TT102 calls ping


.ping

 LDX #1                 \ We want to copy the X- and Y-coordinates of the
                        \ current system in (QQ0, QQ1) to the selected system's
                        \ coordinates in (QQ9, QQ10), so set up a counter to
                        \ copy two bytes

.pl1

 LDA QQ0,X              \ Load byte X from the current system in QQ0/QQ1

 STA QQ9,X              \ Store byte X in the selected system in QQ9/QQ10

 DEX                    \ Decrement the loop counter

 BPL pl1                \ Loop back for the next byte to copy

 RTS                    \ Return from the subroutine