Joe Giacobello skrev:
> Peter, many thanks for your tip regarding hot plugging and that seems
> to have been my problem here. I'm curious to know just exactly what
> you mean by hot plugging. Should one not disconnect the serial plug
> while data are flowing or when any electrically active sending or
> receiving device is connected? In other words, should all the units
> in such a system be "off"?
>
> Frankly, I have been using and working with computers since the days
> of the Vic 20 and I wasn't aware of the sensitivity of UARTs to that
> kind of failure. Apparently, it's a well known problem.
>
> 73, Joe
> K2XX
>
Hi Joe,
Hot plugging is simply the practice of plugging or un-plugging the cable
while the connected devices are powered up.
In this case the DB-25/DB-9 connectors have not been designed to have
guarantied GND connection established before any other pins have a
chance of connecting with their counterpart. Couple that with the common
practice of running computers and other electronic gear without a
safety-ground connection (against all recommendations or even
requirements for installation), is begging for trouble. All computer
power-supplies have filters in their mains input, employing a capacitive
potential divider between the phase and return, with the midpoint tied
to ground. If the ground is allowed to float, or just have a rather high
resistance to ground, there may be as much as a 115V (with 230V mains)
AC ground potential on the device. Connecting such a device to other
electronic devices, with other ground potential, is clearly a recipe for
failures.
--
Vy 73 de OZ1PIF/5Q2M, Peter
** CW: Who? Me? You must be joking!! **
email: peter(no-spam-filler)@frenning.dk
http://www.frenning.dk/oz1pif.htm
Ph. +45 4619 3239
Snailmail:
Peter Frenning
Ternevej 23
DK-4130 Viby Sj.
Denmark
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