Keyboard: DODKS4

       Name: DODKS4                                                  [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Implement the #DODKS4 command (scan the keyboard to see if a
             specific key is being pressed)
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * OSWVECS calls DODKS4


 This routine is run when the parasite sends a #DODKS4 command with parameters
 in the block at OSSC(1 0). It scans the keyboard to see if the specified key
 is being pressed.


 Arguments:

   OSSC(1 0)            A parameter block as follows:

                          * Byte #2 = The internal number of the key to check

                        See p.142 of the Advanced User Guide for a list of
                        internal key numbers


 Returns:

   OSSC(1 0)            A parameter block as follows:

                          * Byte #2 = If the key is being pressed, it contains
                            the original key number from byte #2, but with bit 7
                            set (i.e. key number + 128). If the key is not being
                            pressed, it contains the unchanged key number


.DODKS4

 LDY #2                 \ Fetch byte #2 from the block pointed to by OSSC, which
 LDA (OSSC),Y           \ contains the key to check, and store it in A

 DKS4                   \ Include macro DKS4 to check whether the key in A is
                        \ being pressed, and if it is, set bit 7 of A

 STA (OSSC),Y           \ Store the updated A in byte #2 of the block pointed to
                        \ by OSSC

 RTS                    \ Return from the subroutine