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
> >
> >
> >
>

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