Lee Wright wrote:
> Thankyou to all that replied to my post it has been most helpful.    The
> difference between the oscilator accuracy for the 16f628 & the 16f628A is
> very interesting indeed.   Upon closer inspection I note that the chip is in
> fact the 16f628A.       I think maybe my problem lies somewhere else,  maybe
> the variables are getting messed up inside the chip before being transmitted
> back.
<snip>
> It only occured to me later but I have been getting reliable
> comms at 250K (yes 250,000bps) using a 28A on another project with internal
> osc but that was with RS285 and SN75176 drivers/receivers.
<snip>

This shouldn't be glossed over; I'm an old guy, and I can say what needs
to be said here.

You need to listen carefully to what Olin, myself and many others have
said here and before about designing for reliability, in this case in
regard to internal oscillator stability.

What we are saying is that it is ALWAYS easy to design one or two of
something and it'll work perfectly without regard to the manufacturers'
specs. That's because the laws of statistics can sometimes bend your way
accidentally, i.e. you were lucky (you KNOW that is true, because in Las
Vegas, sometimes people win). As long as you don't come to DEPEND on
this luck, you'll be OK.

What does it gain your client if you have a product that works fine
unless it is a cold day, or a hot day, or if the F628 is hand-selected,
or if the battery doesn't drop too low? As a designer, it is your
responsibility to design something that ALWAYS works.

Now, back to my week-old turkey sandwich...

--Bob


--
              --------------
                Bob Axtell
        PIC Hardware & Firmware Dev
          http://beam.to/baxtell
              1-520-219-2363

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