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 > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist