Dmitry Kiryashov says:
You can't apply btfss/btfsc operations to [the W register]. You need to put W value to some temp location first and finally check temp with btfss/btfsc commands.
- ANDLW 0x80 ; will test bit .7 in W, other bits are cleared ;-) ANDLW 0x40 ; test bit .6 ;...
result of operation in _Z flag (=0 means bit=1 otherwise bit=0 result to _Z=1)
ANDLW is destructive command. You cannot restore W if you didn't save it before.
- ADDLW 0x88 ; will test bits .7 and .3
results of operation in _C and _DC flags. To restore initial W just ADDLW -0x88 ;-)
- You can also apply XORLW value command to check identity W to some value. It is useful command (sometimes) 'cause you can do comparison for alot of values and restore W after that to initial value.XORLW A_CONST SKPNZ GOTO A_CONST_MATCH XORLW B_CONST^A_CONST ;compare with B_CONST SKPNZ GOTO B_CONST_MATCH XORLW C_CONST^B_CONST ;compare with C_CONST ;.... XORLW LAST_CONST ;last used const value -> restore initial W ;.....
David A Cary of Motorguide Pinpoint Says: " Hint #3 is explained in more detail (with macros that make it easier to write compact, correct code). "
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<A HREF="http://piclist.com/techref/microchip/math/bit/testbitsw.htm"> PIC Microcontoller Bit Math Method Testing bits in W</A>
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