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'[EE] Plugging in an RS232 plug with computer on'
2005\10\08@163109 by John Nall

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It seems to me that I remember hearing somewhere that one should not
plug in a device to a PC while the PC is running, where the devices uses
an RS232 interface.  Does this have the potential for causing damage to
either the device or the PC?  I know that a USB plug can be inserted or
taken out while the PC is running, but have always thought that an RS232
plug should not be.  Does anyone know?

John

2005\10\08@173323 by Dave Wheeler

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face
John,

You will almost certainly get replies both ways. However, I was on a job
in Portugal recently where the customer had blown up the serial driver
chip on an embedded CPU which was caused by both the PC and the
equipment being switched on. It went along the lines of, finished
commissioning using one PC, swapped to customers PC, never worked again
and 2 days later I was on a plane. Once bitten eh ??

Dave

John Nall wrote:

> It seems to me that I remember hearing somewhere that one should not
> plug in a device to a PC while the PC is running, where the devices
> uses an RS232 interface.  Does this have the potential for causing
> damage to either the device or the PC?  I know that a USB plug can be
> inserted or taken out while the PC is running, but have always thought
> that an RS232 plug should not be.  Does anyone know?
>
> John


2005\10\08@174553 by John Nall

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Dave Wheeler wrote:

> > You will almost certainly get replies both ways. However, I was on a
> job in Portugal recently where the customer had blown up the serial
> driver chip on an embedded CPU which was caused by both the PC and the
> equipment being switched on. It went along the lines of, finished
> commissioning using one PC, swapped to customers PC, never worked
> again and 2 days later I was on a plane. Once bitten eh ??


Well, if replies go both ways, then I will choose the safer route.  
:-)   Even better than being once bitten is listening to someone who has
been bit before.  Thanks.

John

2005\10\08@180357 by olin piclist

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John Nall wrote:
> Well, if replies go both ways, then I will choose the safer route.
> :-)   Even better than being once bitten is listening to someone who has
> been bit before.

I hot plug RS-232 frequently, surely 1000s of times by now.  I have never
once found that to damage anything when both ends were proper devices.

RS-232 is deliberatly specified to handle a decent voltage range, be short
circuit proof, etc.  The only problem I can see is if the two devices are
floating with respect to each other and static electricity builds up between
them.  Even then that should be OK if the shields are properly connected
because they would make contact first.  I always make sure the sheild is
connected to ground on stuff I build, but you could have a cable that
doesn't wire the shield accross.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\10\08@182449 by Dave Wheeler

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face
I have also 'hot plugged' many times, however when a £12,000 bit of kit goes pop, has to be shipped back to the UK for repair, I become 'cautious' :-)

In the Fire Alarm industry, it is quite common for shields (screens) to only be grounded at one end ( I thought it was normal in most applications to reduce EMC problems). Lightning can do wonderful things when it has a low impedance path.
The one that annoys me is when the 0V rail is connected to ground, I have seen professional equipment with a DB9 and pin 5 connected to the shield, causes havoc with Ground Fault monitoring.

Dave


Olin Lathrop wrote:

{Quote hidden}

2005\10\08@212404 by Xiaofan Chen

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I heard that people with self-built JDM programmer burnt their
PC COM port when hotplugging.

I heard that some Intel chipset based Motherboards got the
ICH4 south bridge burned when user hotplugged USB
device. Often the culprit is the cheaper casing used.

Regards,
Xiaofan

http://tw.giga-byte.com/Motherboard/Support/FAQ/FAQ_456.htm

The ICH4/5 SouthBridge chipset on my Intel(r) motherboard appears
damaged or "burnt". How did this happen?

The GIGABYTE Global RMA Service Center has recently become aware of
the randomly occurring risk to ICH4/5 SouthBridge chipsets on Intel(r)
motherboards to become damaged or "burnt" when a USB device is
connected. Please read the following paragraphs to learn more about
this issue.

Why did this happen?

There are three likely causes:

1) Accumulated static electricity from the human body may have been
transmitted to the ICH4/5 SouthBridge chipset when connecting a USB
device if it has not been "grounded".

2) A connected USB device does not have any static electricity protection.

3) Accumulated static electricity in a front-panel USB port that is
not properly "grounded" with the PC casing.


Usage Tips


Avoid touching the USB connector.

Release static electricity within your USB device by touching the USB
connector to any metal surface before plugging it into your computer.

Use rear-panel USB ports on your PC whenever possible.

Use a three-pronged electrical cord to connect a power supply to your PC.

Use only approved or certified power supplies.

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