> > As far as I know, the new TRIS setting takes effect at the end of the
cycle.
> > I bet the chip switches this internally very fast.  It might take the
> > external circuit a little time to react, especially when changing to
high
> > impedance.
> >
>
>    That's what I'm thinking might be happening. I've gotten
> a few spurious results with a couple variations of the code (Totally
> incorrect results, but I've received bytes other than 0xFF and 0x00
> a few times.)
>
>    What can be done to stablize the wire faster?

That depends on the external circuit.  If it is a passive pull up/down, then
you can decrease its impedence.  If something else takes over and drives the
line, then you want it so start driving as soon as possible after setting
TRIS.

> > Is it possible that 1920 is the bytes/second rate?  That would come out
to
> > 19,200 bits/second.
> >
>
>    That was my thought, too, when I heard they ran at 1920, since
> it's just _too_ coincidental. OTOH, these were made in 1989, quite
> possibly earlier...

1989 is still *long* after 19,200 was a common baud rate.  The higher baud
rates came about as "glass teletype" terminals became common.  Most of the
klunkety klunk mechanical teletypes topped out at 300 baud.  The "standard"
baud rates above that are mostly power of two mutiples of 300 baud.  For a
long time from about mid 70s to late 80s 19200 was the fastest baud rate you
could pretty much expect most non-mechanical equipment to be capable of.

> I've got a few more versions of the code to
> try out tonight, so I think I'm going to try a few variations
> running at 19200 instead.

It would be better just to measure it with a scope than poke in the dark.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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