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