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⌂ ∞ Elite on the BBC Micro and NES

Keyboard: scan_fire

[Elite-A, Parasite]

       Name: scan_fire                                               [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Check whether the joystick's fire button is being pressed by
             sending a scan_fire command to the I/O processor

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DKJ1 calls scan_fire
             * TITLE calls scan_fire




.scan_fire

 LDA #&89               \ Send command &89 to the I/O processor:
 JSR tube_write         \
                        \   =scan_fire()
                        \
                        \ which will check whether the fire button is being
                        \ pressed and return the result in bit 4 of the returned
                        \ value

 JMP tube_read          \ Set A to the response from the I/O processor, which
                        \ will have bit 4 clear if the fire button is being
                        \ pressed, or set if it isn't, and return from the
                        \ subroutine using a tail call