You are looking in the wrong places:

option does set prescaler assignment and prescaler value, but CONFIG
enables or disables it.

CONFIG is located above normal program space and is not in ram.

Normally OPTION is in page 1 (not page 0) data memory, so to change it
you can do this:
        movlw   option
        movwf   indf
        movlw   b'00010111'        ; insert YOUR data here.
        movwf   indf



to turn watchdog on:
in MPASM;
        #include        <P16C715.inc>  ;(replace with your processor)
        __CONFIG        _WDT_ON & _XT_OSC & _PWRTE_ON & _CP_OFF & _BODEN_on &
_MPEEN_OFF
                        ; (above for 16C715, delete non applicable)

when burning the chip if using PICSTART+ then the above CONFIG
parameters will be automatically burned into the chip. note: most new
MICROCHIP JW parts will be spoiled if you set Code Protect to on as
further erasures will fail  !!!


Trond Georg Andersen wrote:
>
> I think you need to make sure you are on the right page to write to the OPTION
 register.
> trond
> >
> > I'm trying to use the watchdog timer on a PIC16C63.
> >
> > How do I turn it on?
> >
> > So far I'm able to write to the options register as follows:
> >
> > movlw   b'00001111'   ; Program WDT to 128 * .018ms = 2.3 seconds
> > movwf   81h
> >
> > Note: For some reason I couldn't write to OPTION, the assembler did not
> > recognize this word.
> >
> > I have a main loop in my program where I plan on inserting a
> >
> > CLRWDT
> >
> > to reset the watchdog....unless I"m missing a real obvious one, I can't
> > figure out how to start this
> > thing ticking!!
> >
> > Thanks in advance....