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Why is access denied on a serial com port?

Posted on 2004-08-29
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Last Modified: 2012-06-27
I am running Win XP with SP2, AMD3000, 784mb RAM. The MOBO has one serial connection, designated Com 1.  This connection has worked before (albeit a few months ago) but it is not communicating now.  There are no conflicts, it is present and working properly in device manager.  System Info shows it is there and "busy".  I have tried a different serial device and the results are the same for both, it is not available.  Also I have tried one of the devices with a USB > serial adapter and it worked, so we can discount the external hardware.
I have installed a USB Bluetooth adapter but it is not plugged in.  The only thing that gives me cause for concern, but it should'nt, is Activesync connecting a Dell PDA with USB cradle.

I have turned off my AV softare and firewall but it still does not work.  (The XP firewall is off)

Therefore, how do I check what software could be using the port?

What else could be blocking access to it?
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Question by:cabbs
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Accepted Solution

by:
Arl earned 200 total points
ID: 11926914
Hi,

In this case, have you already tried to delete the port and make it detected again ?
Using the DM.

Also, you can try in DM to check for the hidden devices, sometimes that could happen with that :
in DM : "View" -> Show Hidden Devices.
Also, try to reset -> in the settings "Restore Defaults" but ...

Anyway, if this is a software "conflict" -> try to open the Task Manager and delete one by one and check which one could be the problem... and normally the name of the process should be enough to know which software is the guilty one.

Hope that can help.
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by:Fairco
Fairco earned 200 total points
ID: 11927003
This question was asked before here: http://www.experts-exchange.com/Hardware/Modems/Q_20999570.html
But, that thread will be likely abandoned and deleted, so I repeat my post here too:

Download and run Sysinternal's Process Explorer ( http://www.sysinternals.com/ntw2k/freeware/procexp.shtml ).
Select Find / Find Handle, then enter "\device\serial" as search string (without the double quotes of course). This will show which process(es) are holding the COM port. \device\serial0 equals to COM1, \device\serial1 is COM2, and so on. You will be likely find only \device\Serial0, as you mentioned only one COM port.
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Author Comment

by:cabbs
ID: 11929425
Firstly, thanks to you both, it is now working.  I did a search using different criteria but did'nt spot that string, sorry.

I downloaded and checked for other progs, no joy, went to DM and it was disabled.  I know for a fact that when I was playing with it before it was enabled, but I must have left it disabled at the end of that session!  Having enabled it it all started to work.

Therefore, seeing as both solutions worked I think it only fair to increase and split the points 200/200.  Is this acceptable to you both?

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Expert Comment

by:Arl
ID: 11929921
Hi,

You are the master of the question...
That will be fair enough for me.

But thanks for asking.
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