Ruben, now that's a good idea. Let me have a look how a short between RB4
and RB5 affects my other software...

Thanks.

Peter


-----Urspr=FCngliche Nachricht-----
Von: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] Im Auftrag von
Ruben J=F6nsson
Gesendet: Montag, 17. August 2009 12:27
An: Microcontroller discussion list - Public.
Betreff: Re: [PIC] Help me to confirm a strange idea

What is on GP4? Maybe you can connect GP5 to GP4 instead of VDD?

/Ruben

> =

> Hello,
> =

> I got a project ready to go into serial production and now my customer =

> stepped up with an additional idea. He likes to have different =

> features with 2 differerent models, but hardware unchanged. It would =

> be possible to load differerent software by ICSP, but I had another idea
this morning:
> =

> I'm using a 12F519 with an unused RB5 pin. The circuit is powered all =

> the time by 3V and just exits sleep mode when active. Now my idea is =

> to use a "universal software" for both models and simply check the =

> state of RB5 to decide which part of software to run. I don't like to =

> solder tiny wires from RB5 to Vss or Vdd respectively, so I thought of the
following:
> =

> RB5 is located near Vdd, so I simply make a short between Vdd and RB5 =

> if I like to have model 2 (or leave everything as is for model 1).
> When starting up the circuit the first time or when batteries are =

> changed the software looks for the state of RB5. To do this, I output =

> a log.0 to RB5 and read the state immediately. If there is no =

> connection to Vdd it should read zero again. But if there is a connection
it should read log.1.
> =

> I tried this this morning and in fact it works so far, but my concerns
are:
> =

> 1. I'm relying on the fact, that the capacity of the PIC's internal =

> output circuitry is big enough to be stable until my read port function is
done.
> 2. I'm stressing my RB5 port by outputting log.0 to a pin connected to =

> Vdd. How often can I do this? Are there any experiences doing this?
> =

> I know, this is a strange idea, but on the other hand it might be a =

> tricky way with nothing but a soldering point.
> =

> Any comments welcome!
> =

> Best regards
> =

> Peter
> =

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Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
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