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⌂ ∞ ▽ Elite on the 6502

Keyboard: YESNO

[BBC Master version]

       Name: YESNO                                                   [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Wait until either "Y" or "N" is pressed

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




 Returns:

   C flag               Set if "Y" was pressed, clear if "N" was pressed



.YESNO

 JSR t                  \ Scan the keyboard until a key is pressed, returning
                        \ the ASCII code in A and X

 CMP #'Y'               \ If "Y" was pressed, return from the subroutine with
 BEQ PL6                \ the C flag set (as the CMP sets the C flag, and PL6
                        \ contains an RTS)

 CMP #'N'               \ If "N" was not pressed, loop back to keep scanning
 BNE YESNO              \ for key presses

 CLC                    \ Clear the C flag

 RTS                    \ Return from the subroutine