>On Thu, 18 Dec 1997 15:43:12 +0000, Keith Howell wrote:

> Observation: Same PIC works on one board but not another.
> Axiom: The problem is caused by some difference between the boards.
> Thinks: just what are the differences?
> If you can't deduce the problem, test it by experiment.
> Change the circuit or components step by step until the iffy board
> should be exactly like the good one.
> At some point, the offending difference should disappear.

Well, yes, but where to begin?  The demo boards are about ten times as
complex as what I need, and I'm not sure which parts are important and
which are only important if I'm using an EEPROM chip or a keypad or a
battery or whatever.

> What is your app, so we have an idea of how complex it is.

It is (embarrassingly) simple.  It's similar to an LCD clock, with
regular (2 sec) Timer1 ticks triggering updates to an LCD.  There will
be a couple of other inputs, but they're not installed yet, so for
now, it's a clock.  (On my board, the code apparently never makes it
to the Timer1 interrupt enable, though.)

> Problems I have met: People giving me boards with wrong crystal
> values.  Code not initialising variables to zero (this reduces the
> number of random start-up states) Floating inputs not properly
> pulled up (found when debugging an 80C188 design!)  The crystals may
> be the same frequency, but are they the same cut/mode?  (32.768
> xtals are meant to run in Low Power oscillators - maybe one has be
> over driven and damaged and ticking erratically) Try it without the
> LCD.

Thanks for the list.  I'll be on it tonight.

-tom

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tomss at ids.net - 401-861-2831 - 42 Forge Rd, Potowomut, RI 02818 USA