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⌂ ∞ Elite on the BBC Micro and NES

Keyboard: RDKEY

[Elite-A, Parasite]

       Name: RDKEY                                                   [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Scan the keyboard for key presses by sending a scan_10in command
             to the I/O processor

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * check_keys calls RDKEY
             * DK4 calls RDKEY
             * DK4_FLIGHT calls RDKEY
             * PAS1 calls RDKEY
             * PAUSE2 calls RDKEY
             * TITLE calls RDKEY




 Returns:

   X                    If a key is being pressed, X contains the internal key
                        number, otherwise it contains 0

   A                    Contains the same as X



.RDKEY

 LDA #&8C               \ Send command &8C to the I/O processor:
 JSR tube_write         \
                        \   =scan_10in()
                        \
                        \ which will scan the keyboard

 JSR tube_read          \ Set A to the response from the I/O processor, which
                        \ will either be the internal key number of the key
                        \ being pressed, or 0 if no key is being pressed

 TAX                    \ Copy the response into X

 RTS                    \ Return from the subroutine