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Re: [TenTec] Hot Plugging

To: k2xx@swva.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>, orion565@yahoogroups.com
Subject: Re: [TenTec] Hot Plugging
From: "Peter Frenning [OZ1PIF]" <peter@frenning.dk>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Wed, 04 Mar 2009 16:23:56 +0100
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
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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