Tony,

My copy of PIC16F87xA manual (DS39582A, page 158)
indicates that C (and DC for that matter) are not
affected by the INCF instruction. Note that because
INCF only increments by one, Z can be tested as if it
were the carry bit, for the INCF.

Only ADD and SUB commands (ADDWF, SUBWF, ADDLW, SUBLW)
affect C/DC. Note also that these commands do not USE
the value of C/DC for the arithmetic calculation. This
requires using bit-test functions when adding
multiple-byte values, as in the numerous math routines
available on piclist.com. On the other hand, it does
not require clearing/setting the C/DC values prior to
these functions.

I would expect that other PICMicro processors are the
similar, but I would check the Instruction Set Summary
to be sure.

Happy pic'n!

--- Tony_K|bek <tony.kubek@FLINTAB.COM> wrote:
> Hi,
> I haven't read most if this thread so at the moment
> I have no
> code to post, however I saw this bit from Scott
> Dattalo:
> <snip>
> >Here's a solution that saves one instruction:
> >
> >    rlf    TMR1L,W       ; read the msb of tmr1L
> --> Carry
> >     incf   TMR1H,W       ;Assume that the low byte
> is about to
> rollover
> >     movwf  TMR1H_buff
> >
> >     movf   TMR1L,W
> >     movwf  TMR1L_buff
> >
> >     skpnc                ;If TMR1L on the first
> read was < 0x80
> >      btfsc TMR1L_buff,7  ;or if the both reads are
> between
> >       decf TMR1H_buff,F  ;0x80 and 0xff then leave
> the high byte alone
>
> Wouldn't the "incf TMR1H,W " possibly trash the
> carry ? (if TMR1H is
> 0xFF)
>
>
> /Tony
>
> --
> http://www.piclist.com hint: To leave the PICList
> mailto:piclist-unsubscribe-request@mitvma.mit.edu


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