Keyboard: DKS4

       Name: DKS4                                                    [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Scan for a particular key press by sending a scan_xin command to
             the I/O processor
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * TT17 calls DKS4


 Arguments:

   X                    The internal number of the key to check


 Returns:

   A                    If the key is being pressed, A contains the original
                        key number in X but with bit 7 set (i.e. key number +
                        128). If the key is not being pressed, A contains the
                        unchanged key number


.DKS4

 LDA #&8B               \ Send command &8B to the I/O processor:
 JSR tube_write         \
                        \   =scan_xin(key_number)
                        \
                        \ which will scan the keyboard for the specified
                        \ internal key number

 TXA                    \ Send the parameter to the I/O processor:
 JSR tube_write         \
                        \   * key_number = X

 JSR tube_read          \ Set A to the response from the I/O processor, which
                        \ will contain the key number with bit 7 set if the key
                        \ is being pressed, or bit 7 clear if it isn't

 TAX                    \ Copy the response into X

 RTS                    \ Return from the subroutine