Peter
Solder an SMD resistor between RB5 and VDD. That way, it's pulled high,
but if you write a '0' to RB5, it won't hurt anything.
Jim
----- Original Message -----
From: "Peter Feucht"
To: "'Microcontroller discussion list - Public.'"
Sent: Monday, August 17, 2009 5:01 AM
Subject: [PIC] Help me to confirm a strange idea
>
> 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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