> Van: Andre Abelian <andre@compufire.com>
> Aan: PICLIST@MITVMA.MIT.EDU
> Onderwerp: fsr
> Datum: maandag 6 april 1998 16:53
>
> Hi to all engineers.
>
> I need to know more about fsr.
> this is what I know.
> Fsr is a software register that can hold up to 255 difference values or
> registers.
> you can store them and you can call them by using INDF instruction.
> Am I right?

Ehhh... Sort of.  The FSR is an register that can (as all other registers)
hold
a number ranging from 0x00 (0 decimal) thru 0xFF (255 decimal).

The INDF register does the same.

Now the tricky part :

The data stored into INDF will _not_ be stored at adres 0x00 (where INDF
is located), but at the adres FSR points to.

Example:

movlw 0x50
movwf FSR
incf INDF

This will increment Register 0x50 by one.

movlw 0x03
movwf FSR
btfss INDF,0
goto {somewhere}

This will branch to {somewhere} if the carry is not set.
(register 0x03 is the Status-register, bit 0 is the Carry-flag)

> this is what I do not know.
> 1. what is the real purpose of this? when do you use it?

Observe the next routine :

  movlw 0x20
  movwf FSR
  goto CharOut2
CharOut1:
movf INDF,w
  {write the character to LCD, RS232, etc}
  inc FSR
CharOut2:
  movf INDF
  btfss STATUS,Z
  goto CharOut1

This routine will output bytes (the routine between {} ) found at 0x20 and
on,
stopping when it encounters a 0x00 byte (movf INDF , btfss STATUS,Z)

Very handy if you want to write text from an internal buffer to a LCDisplay

The other way around, you could receive bytes from an RS232 connection,
and save them in internal memory by using an
  movwf INDF
  inc FSR
combination.

> 2. when you store values how does it organize.
>
> for example.
>
> movlw     0x01
> movwf    fsr
> movlw    0x02
> movwf    fsr
> movlw    0x03
> movwf    fsr
>
> is this means that fsr (file select register) saved all 3  values or
> only the last one?

This example loads 0x03 in FSR.  All other values where overwritten by the
last one.  In this way you are using the FSR register as a normal (not
dedicated) storage register.

> could you please explaine more.
>
See & read the above ;-)

> Andre                        thank you

Need to know more ? Just tell us/me ...

Greetz,
  Rudy Wieser