Keyboard: U%

       Name: U%                                                      [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Clear the key logger
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DEATH calls U%
             * DOKEY calls U%


 Returns:

   A                    A is set to 0

   Y                    Y is set to 0


.U%

 LDA #0                 \ Set A to 0, as this means "key not pressed" in the
                        \ key logger at KL

 LDY #15                \ We want to clear the 15 key logger locations from
                        \ KY1 to KY19, so set a counter in Y

.DKL3

 STA KL,Y               \ Store 0 in the Y-th byte of the key logger

 DEY                    \ Decrement the counter

                        \ --- Mod: Code removed for Demonstration Disc: ------->

\BNE DKL3               \ And loop back for the next key, until we have just
\                       \ cleared KL+1. We don't want to clear the first key
\                       \ logger location at KL, as the keyboard table at KYTB
\                       \ starts with offset 1, not 0, so KL is not technically
\                       \ part of the key logger (it's actually used for logging
\                       \ keys that don't appear in the keyboard table, and
\                       \ which therefore don't use the key logger)

                        \ --- And replaced by: -------------------------------->

 BPL DKL3               \ And loop back for the next key, until we have just
                        \ cleared KL, so this not only clears the key logger,
                        \ but also the value at KL that is used for logging keys
                        \ that don't appear in the keyboard table

                        \ --- End of replacement ------------------------------>

 RTS                    \ Return from the subroutine