Version analysis of DKS1

       Name: DKS1
       Type: Subroutine
   Category: Keyboard
    Summary: Scan the keyboard for a flight key
  Deep dive: The key logger


 Scan the keyboard for the flight key given in register Y, where Y is the
 offset into the KYTB table above (so we can scan for Space by setting Y to
 2, for example). If the key is pressed, set the corresponding byte in the
 key logger at KL to &FF.


 Arguments:

   Y                    The offset into the KYTB table above of the key that we
                        want to scan on the keyboard


.DKS1

 LDX KYTB,Y             \ Get the internal key number from the Y-th byte of the
                        \ KYTB table above

 JSR DKS4               \ Call DKS4, which will set A and X to a negative value
                        \ if the key is being pressed

 BPL DKS2-1             \ The key is not being pressed, so return from the
                        \ subroutine (as DKS2-1 contains an RTS)

Cassette
Flight
 LDX #&FF               \ Store &FF in the Y-th byte of the key logger at KL
 STX KL,Y
 LDA #&FF               \ Store &FF in the Y-th byte of the key logger at KL
 STA KL,Y

 RTS                    \ Return from the subroutine