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PIC Microcontoller Methods

Detecting a change in a register

In general, you just save the prior state of the port, register, etc.. then compare the current state to that state to check for changes.


Bob Fehrenbach has passed on a number of his snippets for inclusion in my web page and have shown up in this book. The first detects the change in a bit and saves the new data for later execution. This code can be used to detect changes in the I/O Ports, Timers, or other registers that can be updated externally to the software execution.
  movf   Reg, w                 
  andlw  Mask                   ;  Mask out unused bits
  xorwf  old, w                 ;  Compare to previous value
  btfsc  STATUS, Z              ;  If Zero set, bits are the Same
   goto  no_change
  xorwf  old                    ;  Bits are different, Store New 
                                ;   pattern in "old"


See also:

file: /Techref/microchip/regchg.htm, 1KB, , updated: 2004/12/6 11:49, local time: 2021/2/24 20:55,

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