using mclr as an output!

[justDIY]

found this neat article on EDN detailing a trick to use the mclr pin, normally an input only pin, as a digital output.

the trick relies on setting the weak pullup feature inside the pic, using that extremely small current to switch an external mosfet which then controls an external load

**broken link removed**

 

[bananasiong]

Wow.. this is brilliant. I didn't think of making this pin as output since the datasheet states that this pin can only be input. But this won't work for bigger PIC right? As the MCLR is usually not on PORTB and the weak pullup is on PORTB.

Thanks for sharing.

 

[Pommie]

I have used this "function" in the past and actually posted about it 18 months ago in this thread. Unfortunately, most of the new pics don't have the pullup on Mclr.

Mike.

 

[Nigel Goodwin]

Yes, it's a very old 'trick', but only really of limited use.

 

[Pommie]

Yes, it's a very old 'trick', but only really of limited use.

Really, I'd never come across this before I posted it. Maybe you could supply a link.

Mike.

 

[Nigel Goodwin]

Really, I'd never come across this before I posted it. Maybe you could supply a link.

Search the PICList archives, I seem to recall it was mentioned there ages ago.

EDIT: By the way, I wasn't suggesting you hadn't individually 'discovered it'.

 

[justDIY]

i guess it's really only of interest on the 6 and 8 pin devices, when you're in a pinch and just need one more output.

 

[Pommie]

Nigel,

I would be really impressed if you could supply a link. Can I just ask why, if this is an old trick, did you question the value of the pullups in this thread. If you knew this trick then you would have not questioned their value. Maybe you are thinking of this older thread where I also explain how this can be done.

Mike.

 

[Pommie]

i guess it's really only of interest on the 6 and 8 pin devices, when you're in a pinch and just need one more output.

The only device I have come across where it works is the 12F509. All the later devices don't have the pullup on MCLR.

Mike.

 

[Nigel Goodwin]

Nigel,

I would be really impressed if you could supply a link. Can I just ask why, if this is an old trick, did you question the value of the pullups in this thread. If you knew this trick then you would have not questioned their value. Maybe you are thinking of this older thread where I also explain how this can be done.

Perhaps I'm imagining things?, but I've got this thought at the back of my mind that it was on the PICList long ago? - I subscribed to the PICList for a number of years, and read all the posts as they were made - many of which were completely over my head, but lot's of others prompted ideas.

 

[justDIY]

The only device I have come across where it works is the 12F509. All the later devices don't have the pullup on MCLR.

Mike.

the 10f2xx have a software configurable weak pullup on mclr