I'm resending this because I do not believe I sent the correct tag
originally.

If you got it twice, I apologize,

myke
----- Original Message -----
From: "myke predko" <myke@passport.ca>
To: "pic microcontroller discussion list" <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, April 18, 2001 5:46 PM
Subject: Fw: [PIC]: Some questions


> Hi Luis,
>
> Barry explained the various assembler options, but I thought I would have
a
> go at your question on "if"/"Else"/"endif".
>
> These three instructions are "conditional assembly" directives.  You can
use
> these directives for selecting options in your application.
>
> For example, if there was a possibility that you would have to change the
> PCLATH register before executing a "goto" instruction, you could use the
> code:
>
>  if (((HIGH $) & 0x018) != ((HIGH Label) & 0x018))
>   movlw  HIGH Label        ;  If the code page of the Destination
>   movwf  PCLATH            ;   is Different from the current
>                            ;   Code Page, Update PCLATH
>  else                      ;  Code Page of Current = Destination
>   nop                      ;  Do not change the PCLATH Register
>   nop
>  endif
>   goto   Label & 0x07FF    ;  Goto the Specified Label
>
> In the first statement, I am comparing the code page (which is specified
in
> bits 11 & 12 of the address) of the current address against the code page
of
> the destination address.  If they are different, then the PCLATH register
> will be updated to the value of the destination.  Else, PCLATH will not be
> changed.
>
> The "HIGH" directive returns bits 8-15 of the constant it is applied to.
> "&" is the bitwise "AND" operator.
>
> There are a lot of different ways to describe "HIGH":
>
>  HIGH Constant = (Constant & 0x0FF) / 0x0100
>               = (Constant & 255) / 256
>               = (Constant & 0x0FF) >> 8
>               = (Constant >> 8) & 0x0FF
>
>
> I don't know if you were present a few days ago, but there was a
discussion
> about conditional assembly and the possibility of having a different
number
> of instructions depending on the conditional assembly execution path.  If
> you look at the sample code above, you will see if the PCLATH register is
> not updated, then an equal number of "nop" instructions are executed.
This
> was not put in to make sure the timing was the same, but to make sure the
> number of instructions are the same.
>
> If you fail to do this, you will probably get a "Phase Error" which
> indicates that the length of the code generated by the final assembler
pass
> is different from the length of the code generated by the first assembler
> pass.  This type of error is VERY DIFFICULT to find and fix.
>
> If you are new to programming, I would recommend that you do not use
> conditional assembly code as it can be very confusing and has the
> opportunity for difficult problems to find and debug (like the Phase Error
> described above).
>
> myke
> > ----- Original Message -----
> > From: "Luis Fernando Antoniasse" <anbarsystem@riopreto.com.br>
> > To: <PICLIST@MITVMA.MIT.EDU>
> > Sent: Wednesday, April 18, 2001 1:51 PM
> > Subject: [PIC]: Some questions
> >
> >
> > > Hi all,
> > >
> > > I have seen some codes in assembler that I can not undertand
> > > very well.
> > >
> > > For exemple:
> > > What it means, not the instruction but
> > > the codes on the sequence?
> > >
> > > movlw (1<<TMR2 ON) +1
> > > What mean (1<<TMR2 ON)+1
> > >
> > > or
> > > bsf RCSTA ^ 0x080
> > > What mean ^ 0x080
> > >
> > > or
> > > movlw (1<<ADCS1) | (1<<ADON)
> > > What means (1<<ADCS1) | (1<<ADON)
> > >
> > > And what about IF,ELSE,ENDIF?
> > > What is the best way to use this or when I must use this?
> > >
> > > Thanks in advanced,
> > >
> > > Luis Fernando
> > >
> > > --
> > > http://www.piclist.com hint: The list server can filter out subtopics
> > > (like ads or off topics) for you. See http://www.piclist.com/#topics
> > >
> > >
> > >
> >
>

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics