vze27bym@verizon.net wrote:
>
> Hi Bob.
>
> XOR function is really good for that.
> Here is different example with decfsz function (or incfsz).
>
> Ok.
> If value in WREG is 0,1,2,3,4,...  i.e. it's monotonously incrementing
> by some event.. we can do calculated jump (addwf pcl,F for example)
> or simply following. (it's taking more space but faster to develop
> and also we will not end up somewhere unexpected in case of wrong
> switch value as for addwf pcl,F scheme.
>
> test_0:
>         movwf   temp

        tstf    temp

Sorry. Forgot to put here


>         skpz
>         goto    test_1
>
> ;here is WREG=0
> ;...
>         goto    _somewhere
>
> test_1:
>         decfsz  temp,F
>         goto    test_2
>
> ;here is WREG=1
> ;...
>         goto    _somewhere
>
> test_2:
>         decfsz  temp,F
>         goto    test_3
>
> ;here is WREG=1
> ;...
>
> test_3:
> ;and so on...
>
> Bob Ammerman wrote:
> >
> > Here is a neat trick to check for several possible values:
> >
> >     xorlw    value_a
> >     skpnz
> >     goto      it_is_a
> >     xorlw    value_a^value_b
> >     skpnz
> >     goto      it_is_b
> >     xorlw    value_b^value_c
> >     skpnz
> >     goto      it_is_c
> >
> > --- optional to restore original value of W:
> >
> >     xorlw    value_c
> >
> > Bob Ammerman
> > RAm Systems
> >
> > ----- Original Message -----
> > From: "Byron A Jeff" <byron@CC.GATECH.EDU>
> > To: <PICLIST@MITVMA.MIT.EDU>
> > Sent: Monday, March 17, 2003 1:03 PM
> > Subject: Re: [PIC] 16F628 ASM Language question
> >
> > > On Mon, Mar 17, 2003 at 12:46:46PM -0500, CaptMasterX@CS.COM wrote:
> > > > The instruction set for the 16F628 looks kinda skimpy.
> > >
> > > Simplicity by design.
> > >
> > > >  Is there any way to
> > > > test wreg against a certain byte and jump if it's equal.
> > >
> > > Absolutely.
> > >
> > > >  They have
> > > > instructions to test each bit, but to test against a byte,
> > >
> > > Which by the way doesn't work for the Wreg.
> > >
> > > > i'd have to write
> > > > a function to go through and test every bit before i got the answer.  is
> > > > there an easier way?
> > >
> > > Yes. There are two standard ways to do comparitons:
> > >
> > > 1) Subtraction. If you subtract two equal values, the result is zero. So
> > the
> > >    SUBLW instruction would be helpful.
> > > 2) Exclusive Or (XOR). A useful logic function that produces a zero result
> > >    when the values are equal.
> > >
> > > So the "skimpy" instruction set actually has two different instructions
> > (SUBLW
> > > and XORLW) that will accomplish what you need. Just be aware of two
> > things:
> > >
> > > 1) You'll lose the value in W. Each is destructive. If you need the retain
> > >    the value, store it in a register, load the compare value into Wreg,
> > then
> > >    perform the operation between Wreg and the saved register.
> > > 2) After you perform the operation you'll need to check the (Z)ero flag in
> > the
> > >    STATUS register. This is where you use the BTFSS or BTFSC instruction.
> > >
> > > BAJ
> > >
> > > --
> > > http://www.piclist.com hint: To leave the PICList
> > > mailto:piclist-unsubscribe-request@mitvma.mit.edu
> > >
> >
> > --
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