On Wed, 27 Oct 2004, Bob Axtell wrote:

> Olin Lathrop wrote:
>
>> Bob Axtell wrote:
>> 
>>> While it IS a good idea to rewrite the TRIS resisters often (and I do),
>>> 
>> 
>> A good idea in your opinion apparently.  Others here disagree.  I 
>> personally
>> find such tactics silly.
>> 
>> 
> Be careful, Olin, you're going off the reservation again. Apparently you have 
> no experience with
> electronics operating near strong RF or ESD sources. The traces on the PCB 
> act as antennas unless
> very careful hardware design is done. This issue is not a software problem, 
> but the effects might SEEM
> to be so. My experience with this came from Motorola HC05 designs before MC 
> came along. The port
> latches -being near the pins themselves, I guess- changed rather easily under 
> a strong RF field. If anybody
> still designs with these things, try it and see.

Bob,

At Synaptics, we do the 'rewrite tris bit' 30-million times per year. 
That's about how many TouchPads + iPods + other capacitance sensing gizmos 
we ship each year. The main reason is to ensure that the integrity of the 
I/O's are maintained. Our devices are not PICs, but like most processors, 
the output latches are necessarily electrically close to the I/O pins and 
very susceptible to ESD disturbances. Our devices are specifically 
designed to be touched. We try not to descriminate against overly charged 
people (either electrically or personality :). So a 15kV human-body model 
zap on to the surface of TouchPad might cause the TouchPad to reset, but 
seldom will phase the I/O's. The host may not even notice!

Scott
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