Post by thread:Bit Set/Reset problem.....a puzzle!

Dear allies, A friend of mine is writing her first PIC program using the 16C64, and she has asked me this question, because she knows I use PICs, but I can't think of how to do it! Her Problem: If you have a value 'n', ranging from 0-7 in W (or a file reg, whichever makes it work!) How can you use this to set or clear bit 'n' in another file reg. (or W) In other words can you use W or any reg as an indirect bit pointer? If not (and I think not), what is the best way to implement such a function? The best I can think of is something like . . . MOVLW B'11000001' ; for example obviously these values will MOVLW H'02' ; come from somewhere else in the real prog! CALL BITSET IORWF TARGET,1 . . . MOVLW H'06' ; CALL BITCLR ANDWF TARGET,1 . . . BITSET ANDLW H'07' ADDWF PCL,F RETLW B'00000001' RETLW B'00000010' RETLW B'00000100' RETLW B'00001000' RETLW B'00010000' RETLW B'00100000' RETLW B'01000000' RETLW B'10000000' BITCLR ANDLW H'07' ADDWF PCL,F RETLW B'11111110' RETLW B'11111101' RETLW B'11111011' RETLW B'11110111' RETLW B'11101111' RETLW B'11011111' RETLW B'10111111' RETLW B'01111111' Anyone have any better ideas? Am I missing something in the instruction set? I need some help for the sake of my guru-ship! Regards Paul (Preparing to be humble!)

Paul BRITTON wrote: > In other words can you use W or any reg as an indirect bit pointer? Pick another register as pointer, let's call it "ptr". clrc movlw 1 btfsc ptr,1 movlw 4 movwf mask btfsc ptr,0 rlf mask,F btfsc ptr,2 swapf mask,F ; or W if you need that Now you've got your mask value; do what you will with it. This code is isosynchronous, it may be shorter code to rlf mask while decfsz ptr. Concept not original, copied from Dimitry amongst others. -- Cheers, Paul B.

Hi all, "Paul B. Webster VK2BZC" wrote: > Pick another register as pointer, let's call it "ptr". > > clrc > movlw 1 > btfsc ptr,1 > movlw 4 > movwf mask > btfsc ptr,0 > rlf mask,F > btfsc ptr,2 > swapf mask,F ; or W if you need that > Concept not original, copied from Dimitry amongst others. I think the original version (1 cycle less) goes like this: movlw 1 btfsc ptr,1 movlw 4 movwf mask btfsc ptr,0 addwf mask,f btfsc ptr,2 swapf mask,f The 'rlf' is replaced with an 'addwf' thus 'clrc' is not needed anymore. I had also posted a 32 bit version last week for the led bar solution. I copied the technique for a part. The code is also found on the website below. regards, Reggie -- e-mail: spam_OUTrberdinTakeThisOuTbigfoot.com ICQ#: 31651436 URL: http://www.bigfoot.com/~rberdin

On Tue, 2 Mar 1999 18:57:30 +0000 Paul BRITTON <.....Paul.BRITTONKILLspam@spam@MMSUK.CO.UK> writes: >Dear allies, > >A friend of mine is writing her first PIC program using the 16C64, and >she >has asked me this question, because she knows I use PICs, but I can't >think of how to do it! > >Her Problem: If you have a value 'n', ranging from 0-7 in W (or a >file >reg, whichever makes it work!) > How can you use this to set or clear bit 'n' in >another >file reg. (or W) The PIC CPU core doesn't have an instruction to do it directly. A common way is what you've done: translate the bit number to a mask, then use a bytewise AND or OR to clear or set the masked bit. You only really need one mask translation table or routine. Use the mask as is (all 0 except one 1) to set bits with OR, and complememt the mask for the bit-clearing AND instruction. If you need to optimize for speed, maybe a table of bsf or bcf instructions would be faster: setbi rlf bitno,w ;Multiply bit number by 2 andlw b'00001110' ;Keep only relevant bits addwf PCL,f ;jump into table below bsf INDF,0 return bsf INDF,1 return [...] bsf INDF,7 return Thsi routine needs 19 instructions and always takes 9 cycles (including the CALL and RETURN instructions). A corresponding routine would be needed to clear bits. As with any table, ensure that PCLATH is set properly. If you can store the bit number as bitnumber * 2 that would avoid needing to multiply it every time to form the table index. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]

Hi, Mike Keitz wrote: > setbi > rlf bitno,w ;Multiply bit number by 2 > andlw b'00001110' ;Keep only relevant bits > addwf PCL,f ;jump into table below > bsf INDF,0 > return > bsf INDF,1 > return > [...] > bsf INDF,7 > return > > Thsi routine needs 19 instructions and always takes 9 cycles (including > the CALL and RETURN instructions). A corresponding routine would be > needed to clear bits. As with any table, ensure that PCLATH is set > properly. If you can store the bit number as bitnumber * 2 that would > avoid needing to multiply it every time to form the table index. A simple lookup table and masking directly is faster. Only 8 cycles and lesser code space. main_routine: . . . call setbi ;7 iorwf INDF,f ;8 use andwf if clearing . . setbi: movf bitno,w addwf PCL,f retlw B'00000001' ; set to B'11111110' if clearing retlw B'00000010' . . . retlw B'10000000' regards, Reggie