12F508 OPTION Register

[sayzer]

Has anyone successfully written to OPTION register in 12F508?

This register is not recognized and has no address !

[HenrikOlsson]

Hi,
Looks like you need to resort to a bit of assembly to get to it.

The OPTION register is a 8-bit wide, write-only register, which contains various control bits to configure the Timer0/WDT prescaler and Timer0.
By executing the OPTION instruction, the contents of the W register will be transferred to the OPTION register.
A Reset sets the OPTION<7:0> bits.

Now, I truly suck at assembly but if I were to try anything it would probably be something like:

ASM
MOVLW 128   ; Put 128 in W (enable weel pullup).
OPTION         ; Move content of W to OPTION
ENDASM

/Henrik.

[sayzer]

Thanks Henrik,

I made a simple flip flop code; and even it did not work. So, I can not test whether your suggestion actually works or not.

There must be something specific with the programming of this chip.

Even though I get no error when programming, I can't get it work.

[Agent36]

Hi,
Looks like you need to resort to a bit of assembly to get to it.
Now, I truly suck at assembly but if I were to try anything it would probably be something like:

ASM
MOVLW 128   ; Put 128 in W (enable weel pullup).
OPTION         ; Move content of W to OPTION
ENDASM

/Henrik.

Thanks Henrick, that assembly code helped me out with the 12f508. You have to TAB in once then write the code to remove errors.
GPIO.2 and 3 work fine now. Cheers Nick

[Meriachee]

Is this the same kind of process that might be used to get the TOCKI on Portc.5 to be used as a gpio? Any ideas?
The datasheet says:
On power-up, TOCKI functionality is enabled in the OPTION register and must be disabled to allow RC5 to be used as general purpose I/O.
However, noplace does it state how to do that.

[Meriachee]

p.s.
That's on the 16f505 chip, not the 508

[Darrel Taylor]

The OPTION register is accessed the same as any other 16F. PBP translates it to an assembly OPTION command on 12-bit cores.

To use RC5 as an output pin, use ...

OPTION_REG.5 = 0

[Meriachee]

Thanks Darrell, worked like a charm. Options are not so clear in the documentation.