How Windows select which COM port to use

NTDEV
1

Hi,

I’ve one USB-to-RS232 device connected to Windows. May I know how Windows select which COM port this device used?

I’ve one Windows application that will use the virtual COM port. The user might not know the COM port used. So, in the application, I need to auto select the virtual COM port for the user. In order to do this, I need to know how Windows selects(assigns) the COM port number to the device.

By the way, how many virtual COM port that Windows can support?

PS: Windows = WinXP,Win2K,WinME

Thanks.

Regards,

Tan Teik Chuan

Find love online with MSN Personals.

2

Windows maintains a list of assigned com port names and assigns the new
port the next available name. for this to happen, the device must be
installed in the "Ports" device class with the correct "PortSubClass"
value in the INF. There is no way to know ahead of time which COM port
name will be assigned. You have to let the user choose the com port.
For instance, what if the user wants to use another com port with the
application? If you know/can find the device instance for your
particular device, you can read the "PortName" value from the device
node.

Windows can support an infinite number of COM ports, but after COM9, you
must open up the port with the "\.\COMX" syntax instead of COMX (the
\.\COMX syntax works from COM1-9).

d

From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
Sent: Monday, April 17, 2006 9:15 PM
To: Windows System Software Devs Interest List
Subject: [ntdev] How Windows select which COM port to use

Hi,
I've one USB-to-RS232 device connected to Windows. May I know how
Windows select which COM port this device used?
I've one Windows application that will use the virtual COM port. The
user might not know the COM port used. So, in the application, I need to
auto select the virtual COM port for the user. In order to do this, I
need to know how Windows selects(assigns) the COM port number to the
device.
By the way, how many virtual COM port that Windows can support?
PS: Windows = WinXP,Win2K,WinME
Thanks.

Regards,
Tan Teik Chuan

Find love online with MSN Personals.

Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

To unsubscribe, visit the List Server section of OSR Online at

3

Below is taken from .inf of my device.

[Version]
Signature=“$Windows NT$”
Class=Ports
ClassGuid={4D36E978-E325-11CE-BFC1-08002BE10318}
Provider=%MCHP%
LayoutFile=layout.inf
DriverVer=03/31/2006,1.0.0000.0

[DriverInstall.nt.AddReg]
HKR,DevLoader,*ntkern
HKR,NTMPDriver,usbser.sys
HKR,EnumPropPages32,“MsPorts.dll,SerialPortPropPageProvider”
HKR,PortSubClass,1,01

You can see that I’ve set the device class Ports and PortSubClass, but
Windows still cannot assign the next available name for my device. It’s
assigning COM9 to my device. My desktop only have COM1 and COM2.

I am new to Windows Driver. So please bear with me if my question seems to
be ‘funny’.

Thanks.

Regards,
Tan Teik Chuan

From: “Doron Holan”
>Reply-To: “Windows System Software Devs Interest List”
>
>To: “Windows System Software Devs Interest List”
>Subject: RE: [ntdev] How Windows select which COM port to use
>Date: Mon, 17 Apr 2006 21:22:08 -0700
>
>Windows maintains a list of assigned com port names and assigns the new
>port the next available name. for this to happen, the device must be
>installed in the “Ports” device class with the correct “PortSubClass”
>value in the INF. There is no way to know ahead of time which COM port
>name will be assigned. You have to let the user choose the com port.
>For instance, what if the user wants to use another com port with the
>application? If you know/can find the device instance for your
>particular device, you can read the “PortName” value from the device
>node.
>
>Windows can support an infinite number of COM ports, but after COM9, you
>must open up the port with the “\.\COMX” syntax instead of COMX (the
>\.\COMX syntax works from COM1-9).
>
>d
>
>
>From: xxxxx@lists.osr.com
>[mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
>Sent: Monday, April 17, 2006 9:15 PM
>To: Windows System Software Devs Interest List
>Subject: [ntdev] How Windows select which COM port to use
>
>Hi,
>I’ve one USB-to-RS232 device connected to Windows. May I know how
>Windows select which COM port this device used?
>I’ve one Windows application that will use the virtual COM port. The
>user might not know the COM port used. So, in the application, I need to
>auto select the virtual COM port for the user. In order to do this, I
>need to know how Windows selects(assigns) the COM port number to the
>device.
>By the way, how many virtual COM port that Windows can support?
>PS: Windows = WinXP,Win2K,WinME
>Thanks.
>
>Regards,
>Tan Teik Chuan
>
>
>
>Find love online with MSN Personals.
>—
>Questions? First check the Kernel Driver FAQ at
>http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at
>http://www.osronline.com/page.cfm?name=ListServer
>
>—
>Questions? First check the Kernel Driver FAQ at
>http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at
>http://www.osronline.com/page.cfm?name=ListServer

_________________________________________________________________
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4

COM Ports should be allocated via the COM Arbiter map.

It’s a 32 byte (yes byte… NOT bit) value called “ComDB” under
HKEY_LOCAL_MACHINE, “System\CurrentControlSet\Control\COM Name
Arbiter”…

BR,

Rob Linegar
Software Engineer
Data Encryption Systems Limited
www.des.co.uk | www.deslock.com

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
Sent: 18 April 2006 07:46
To: Windows System Software Devs Interest List
Subject: RE: [ntdev] How Windows select which COM port to use

Below is taken from .inf of my device.

[Version]
Signature=“$Windows NT$”
Class=Ports
ClassGuid={4D36E978-E325-11CE-BFC1-08002BE10318}
Provider=%MCHP%
LayoutFile=layout.inf
DriverVer=03/31/2006,1.0.0000.0

[DriverInstall.nt.AddReg]
HKR,DevLoader,*ntkern
HKR,NTMPDriver,usbser.sys
HKR,EnumPropPages32,“MsPorts.dll,SerialPortPropPageProvider”
HKR,PortSubClass,1,01

You can see that I’ve set the device class Ports and PortSubClass, but
Windows still cannot assign the next available name for my device. It’s
assigning COM9 to my device. My desktop only have COM1 and COM2.

I am new to Windows Driver. So please bear with me if my question seems
to
be ‘funny’.

Thanks.

Regards,
Tan Teik Chuan

From: “Doron Holan”
>Reply-To: “Windows System Software Devs Interest List”
>
>To: “Windows System Software Devs Interest List”
>Subject: RE: [ntdev] How Windows select which COM port to use
>Date: Mon, 17 Apr 2006 21:22:08 -0700
>
>Windows maintains a list of assigned com port names and assigns the new
>port the next available name. for this to happen, the device must be
>installed in the “Ports” device class with the correct “PortSubClass”
>value in the INF. There is no way to know ahead of time which COM port
>name will be assigned. You have to let the user choose the com port.
>For instance, what if the user wants to use another com port with the
>application? If you know/can find the device instance for your
>particular device, you can read the “PortName” value from the device
>node.
>
>Windows can support an infinite number of COM ports, but after COM9,
you
>must open up the port with the “\.\COMX” syntax instead of COMX (the
>\.\COMX syntax works from COM1-9).
>
>d
>
>
>From: xxxxx@lists.osr.com
>[mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
>Sent: Monday, April 17, 2006 9:15 PM
>To: Windows System Software Devs Interest List
>Subject: [ntdev] How Windows select which COM port to use
>
>Hi,
>I’ve one USB-to-RS232 device connected to Windows. May I know how
>Windows select which COM port this device used?
>I’ve one Windows application that will use the virtual COM port. The
>user might not know the COM port used. So, in the application, I need
to
>auto select the virtual COM port for the user. In order to do this, I
>need to know how Windows selects(assigns) the COM port number to the
>device.
>By the way, how many virtual COM port that Windows can support?
>PS: Windows = WinXP,Win2K,WinME
>Thanks.
>
>Regards,
>Tan Teik Chuan
>
>
>
>Find love online with MSN Personals.
>—
>Questions? First check the Kernel Driver FAQ at
>http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at
>http://www.osronline.com/page.cfm?name=ListServer
>
>—
>Questions? First check the Kernel Driver FAQ at
>http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at
>http://www.osronline.com/page.cfm?name=ListServer

_________________________________________________________________
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—
Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

To unsubscribe, visit the List Server section of OSR Online at
http://www.osronline.com/page.cfm?name=ListServer

5

Hi,

I am away from my computer so I will reply with an email.  I don’t have the news reader set up here at the hotel. If you get Winobj.exe from sysinternals.com.  This lets you see the windows objects.  You will see in the ?? directory the COM link to which device it is mapped too.  It is also in the ??\Devices.  This shows you which device gets calls\ed when you do a CreateFile() on that name.  Hope this helps.  You can also paste this into the news group if it does. You can read about device naming parsing / CreateFile in the OSR news groups too. The linked device name will get the IRP_MJ_CREATE on CreateFile from the IO Manager.

 

Sincerely,

William Michael Jones “Mike”

-----Original Message-----
From: Tan Teik Chuan
Sent: Apr 17, 2006 9:15 PM
To: Windows System Software Devs Interest List
Subject: [ntdev] How Windows select which COM port to use







Hi,



I’ve one USB-to-RS232 device connected to Windows. May I know how Windows select which COM port this device used?



I’ve one Windows application that will use the virtual COM port. The user might not know the COM port used. So, in the application, I need to auto select the virtual COM port for the user. In order to do this, I need to know how Windows selects(assigns) the COM port number to the device.



By the way, how many virtual COM port that Windows can support?



PS: Windows = WinXP,Win2K,WinME



Thanks.

Regards,


Tan Teik Chuan






Find love online with MSN Personals.
---
Questions? First check the Kernel Driver FAQ at http://www.osronline.com/article.cfm?id=256

To unsubscribe, visit the List Server section of OSR Online at http://www.osronline.com/page.cfm?name=ListServer
6

The com name arbiter is not a public structure and you are not supposed
to touch this field directly. You need to use the com name DB APIs in
user mode. There is no API in kernel mode, but as a driver you are not
supposed to assign yourself a name…(for a variety of reasons).

d

– I can spell, I just can’t type.
-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Rob Linegar
Sent: Tuesday, April 18, 2006 2:08 AM
To: Windows System Software Devs Interest List
Subject: RE: [ntdev] How Windows select which COM port to use

COM Ports should be allocated via the COM Arbiter map.

It’s a 32 byte (yes byte… NOT bit) value called “ComDB” under
HKEY_LOCAL_MACHINE, “System\CurrentControlSet\Control\COM Name
Arbiter”…

BR,

Rob Linegar
Software Engineer
Data Encryption Systems Limited
www.des.co.uk | www.deslock.com

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
Sent: 18 April 2006 07:46
To: Windows System Software Devs Interest List
Subject: RE: [ntdev] How Windows select which COM port to use

Below is taken from .inf of my device.

[Version]
Signature=“$Windows NT$”
Class=Ports
ClassGuid={4D36E978-E325-11CE-BFC1-08002BE10318}
Provider=%MCHP%
LayoutFile=layout.inf
DriverVer=03/31/2006,1.0.0000.0

[DriverInstall.nt.AddReg]
HKR,DevLoader,*ntkern
HKR,NTMPDriver,usbser.sys
HKR,EnumPropPages32,“MsPorts.dll,SerialPortPropPageProvider”
HKR,PortSubClass,1,01

You can see that I’ve set the device class Ports and PortSubClass, but
Windows still cannot assign the next available name for my device. It’s
assigning COM9 to my device. My desktop only have COM1 and COM2.

I am new to Windows Driver. So please bear with me if my question seems
to
be ‘funny’.

Thanks.

Regards,
Tan Teik Chuan

From: “Doron Holan”
>Reply-To: “Windows System Software Devs Interest List”
>
>To: “Windows System Software Devs Interest List”
>Subject: RE: [ntdev] How Windows select which COM port to use
>Date: Mon, 17 Apr 2006 21:22:08 -0700
>
>Windows maintains a list of assigned com port names and assigns the new
>port the next available name. for this to happen, the device must be
>installed in the “Ports” device class with the correct “PortSubClass”
>value in the INF. There is no way to know ahead of time which COM port
>name will be assigned. You have to let the user choose the com port.
>For instance, what if the user wants to use another com port with the
>application? If you know/can find the device instance for your
>particular device, you can read the “PortName” value from the device
>node.
>
>Windows can support an infinite number of COM ports, but after COM9,
you
>must open up the port with the “\.\COMX” syntax instead of COMX (the
>\.\COMX syntax works from COM1-9).
>
>d
>
>
>From: xxxxx@lists.osr.com
>[mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
>Sent: Monday, April 17, 2006 9:15 PM
>To: Windows System Software Devs Interest List
>Subject: [ntdev] How Windows select which COM port to use
>
>Hi,
>I’ve one USB-to-RS232 device connected to Windows. May I know how
>Windows select which COM port this device used?
>I’ve one Windows application that will use the virtual COM port. The
>user might not know the COM port used. So, in the application, I need
to
>auto select the virtual COM port for the user. In order to do this, I
>need to know how Windows selects(assigns) the COM port number to the
>device.
>By the way, how many virtual COM port that Windows can support?
>PS: Windows = WinXP,Win2K,WinME
>Thanks.
>
>Regards,
>Tan Teik Chuan
>
>
>
>Find love online with MSN Personals.
>—
>Questions? First check the Kernel Driver FAQ at
>http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at
>http://www.osronline.com/page.cfm?name=ListServer
>
>—
>Questions? First check the Kernel Driver FAQ at
>http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at
>http://www.osronline.com/page.cfm?name=ListServer

_________________________________________________________________
Block pop-up ads with MSN Toolbar. http://toolbar.msn.com.my/

—
Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

To unsubscribe, visit the List Server section of OSR Online at
http://www.osronline.com/page.cfm?name=ListServer

—
Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

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http://www.osronline.com/page.cfm?name=ListServer

7

I bet there are other virtual ports created on the machine or you have
moved your device from port to port on the usb hub. COM9 is a fine
value.

d

– I can spell, I just can’t type.

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
Sent: Monday, April 17, 2006 11:46 PM
To: Windows System Software Devs Interest List
Subject: RE: [ntdev] How Windows select which COM port to use

Below is taken from .inf of my device.

[Version]
Signature=“$Windows NT$”
Class=Ports
ClassGuid={4D36E978-E325-11CE-BFC1-08002BE10318}
Provider=%MCHP%
LayoutFile=layout.inf
DriverVer=03/31/2006,1.0.0000.0

[DriverInstall.nt.AddReg]
HKR,DevLoader,*ntkern
HKR,NTMPDriver,usbser.sys
HKR,EnumPropPages32,“MsPorts.dll,SerialPortPropPageProvider”
HKR,PortSubClass,1,01

You can see that I’ve set the device class Ports and PortSubClass, but
Windows still cannot assign the next available name for my device. It’s
assigning COM9 to my device. My desktop only have COM1 and COM2.

I am new to Windows Driver. So please bear with me if my question seems
to
be ‘funny’.

Thanks.

Regards,
Tan Teik Chuan

From: “Doron Holan”
>Reply-To: “Windows System Software Devs Interest List”
>
>To: “Windows System Software Devs Interest List”
>Subject: RE: [ntdev] How Windows select which COM port to use
>Date: Mon, 17 Apr 2006 21:22:08 -0700
>
>Windows maintains a list of assigned com port names and assigns the new
>port the next available name. for this to happen, the device must be
>installed in the “Ports” device class with the correct “PortSubClass”
>value in the INF. There is no way to know ahead of time which COM port
>name will be assigned. You have to let the user choose the com port.
>For instance, what if the user wants to use another com port with the
>application? If you know/can find the device instance for your
>particular device, you can read the “PortName” value from the device
>node.
>
>Windows can support an infinite number of COM ports, but after COM9,
you
>must open up the port with the “\.\COMX” syntax instead of COMX (the
>\.\COMX syntax works from COM1-9).
>
>d
>
>
>From: xxxxx@lists.osr.com
>[mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
>Sent: Monday, April 17, 2006 9:15 PM
>To: Windows System Software Devs Interest List
>Subject: [ntdev] How Windows select which COM port to use
>
>Hi,
>I’ve one USB-to-RS232 device connected to Windows. May I know how
>Windows select which COM port this device used?
>I’ve one Windows application that will use the virtual COM port. The
>user might not know the COM port used. So, in the application, I need
to
>auto select the virtual COM port for the user. In order to do this, I
>need to know how Windows selects(assigns) the COM port number to the
>device.
>By the way, how many virtual COM port that Windows can support?
>PS: Windows = WinXP,Win2K,WinME
>Thanks.
>
>Regards,
>Tan Teik Chuan
>
>
>
>Find love online with MSN Personals.
>—
>Questions? First check the Kernel Driver FAQ at
>http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at
>http://www.osronline.com/page.cfm?name=ListServer
>
>—
>Questions? First check the Kernel Driver FAQ at
>http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at
>http://www.osronline.com/page.cfm?name=ListServer

_________________________________________________________________
Block pop-up ads with MSN Toolbar. http://toolbar.msn.com.my/

—
Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

To unsubscribe, visit the List Server section of OSR Online at
http://www.osronline.com/page.cfm?name=ListServer

8

I did not move my device from port to port. It is always in the same port. Under Device Manager, I can only see COM1 and COM2 before i plug my device in. After I plug it in, COM9 appears. I know that COM9 is fine, but it would be very helpful if Windows can assign the next available COM to my device, which is COM3.

Regards,

Tan Teik Chuan





From: “Doron Holan”
Reply-To: “Windows System Software Devs Interest List”
To: “Windows System Software Devs Interest List”
Subject: RE: [ntdev] How Windows select which COM port to use
Date: Tue, 18 Apr 2006 08:04:11 -0700
>I bet there are other virtual ports created on the machine or you have
>moved your device from port to port on the usb hub. COM9 is a fine
>value.
>
>d
>
>– I can spell, I just can’t type.

Get your ringtones, operator logos and picture messages from MSN Mobile.

9

COM3 is taken. By whom, I don’t know, but it is taken. Do you have Bluetooth software installed? Bth software typically creates a bunch of COM ports for you, so that could be why com3-8 is taken.

What does the contents of HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM say?

d

From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
Sent: Tuesday, April 18, 2006 5:56 PM
To: Windows System Software Devs Interest List
Subject: RE: [ntdev] How Windows select which COM port to use

I did not move my device from port to port. It is always in the same port. Under Device Manager, I can only see COM1 and COM2 before i plug my device in. After I plug it in, COM9 appears. I know that COM9 is fine, but it would be very helpful if Windows can assign the next available COM to my device, which is COM3.

Regards,
Tan Teik Chuan

From:??“Doron Holan”
Reply-To:??“Windows System Software Devs Interest List”
To:??“Windows System Software Devs Interest List”
Subject:??RE: [ntdev] How Windows select which COM port to use
Date:??Tue, 18 Apr 2006 08:04:11 -0700
>I bet there are other virtual ports created on the machine or you have
>moved your device from port to port on the usb hub.??COM9 is a fine
>value.
>
>d
>
>– I can spell, I just can’t type.

________________________________________
Get your ringtones, operator logos and picture messages from MSN Mobile.
—
Questions? First check the Kernel Driver FAQ at http://www.osronline.com/article.cfm?id=256

To unsubscribe, visit the List Server section of OSR Online at http://www.osronline.com/page.cfm?name=ListServer

10

The contents show:

\Device\ltmodem0 COM3

\Device\Serial0 COM1

\Device\Serial1 COM2

\Device\USBSER000 COM9

I do not have Bluetooth software installed.

Regards,

Tan Teik Chuan





From: “Doron Holan”
Reply-To: “Windows System Software Devs Interest List”
To: “Windows System Software Devs Interest List”
Subject: RE: [ntdev] How Windows select which COM port to use
Date: Tue, 18 Apr 2006 19:41:36 -0700
>COM3 is taken. By whom, I don’t know, but it is taken. Do you have Bluetooth software installed? Bth software typically creates a bunch of COM ports for you, so that could be why com3-8 is taken.
>
>What does the contents of HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM say?
>
>d
>
>
>From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
>Sent: Tuesday, April 18, 2006 5:56 PM
>To: Windows System Software Devs Interest List
>Subject: RE: [ntdev] How Windows select which COM port to use
>
>I did not move my device from port to port. It is always in the same port. Under Device Manager, I can only see COM1 and COM2 before i plug my device in. After I plug it in, COM9 appears. I know that COM9 is fine, but it would be very helpful if Windows can assign the next available COM to my device, which is COM3.
>
>Regards,
>Tan Teik Chuan
>
>From: “Doron Holan”
>Reply-To: “Windows System Software Devs Interest List”
>To: “Windows System Software Devs Interest
List”
>Subject: RE: [ntdev] How Windows select which COM port to use
>Date: Tue, 18 Apr 2006 08:04:11 -0700
> >I bet there are other virtual ports created on the machine or you have
> >moved your device from port to port on the usb hub. COM9 is a fine
> >value.
> >
> >d
> >
> >– I can spell, I just can’t type.
>
>
> ________________________________________
>Get your ringtones, operator logos and picture messages from MSN Mobile.
>—
>Questions? First check the Kernel Driver FAQ at http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at http://www.osronline.com/page.cfm?name=ListServer
>
>—
>Questions? First check the Kernel Driver
FAQ at http://www.osronline.com/article.cfm?id=256
>
>To unsubscribe, visit the List Server section of OSR Online at http://www.osronline.com/page.cfm?name=ListServer

Get an advanced look at the new version of MSN Messenger

11

Well, some driver which was previously installed but not currently running claimed those missing ports. Not much more I can recommend as to figuring out who claimed them. Did you ever manually uninstall the usb dongle by deleting reg values?

d

From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
Sent: Tuesday, April 18, 2006 8:35 PM
To: Windows System Software Devs Interest List
Subject: RE: [ntdev] How Windows select which COM port to use

The contents show:
\Device\ltmodem0 COM3
\Device\Serial0 COM1
\Device\Serial1 COM2
\Device\USBSER000 COM9
I do not have Bluetooth software installed.

Regards,
Tan Teik Chuan

From:??“Doron Holan”
Reply-To:??“Windows System Software Devs Interest List”
To:??“Windows System Software Devs Interest List”
Subject:??RE: [ntdev] How Windows select which COM port to use
Date:??Tue, 18 Apr 2006 19:41:36 -0700
>COM3 is taken.??By whom, I don’t know, but it is taken.??Do you have Bluetooth software installed???Bth software typically creates a bunch of COM ports for you, so that could be why com3-8 is taken.
>
>What does the contents of HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM say?
>
>d
>
>
>From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Tan Teik Chuan
>Sent: Tuesday, April 18, 2006 5:56 PM
>To: Windows System Software Devs Interest List
>Subject: RE: [ntdev] How Windows select which COM port to use
>
>I did not move my device from port to port. It is always in the same port. Under Device Manager, I can only see COM1 and COM2 before i plug my device in. After I plug it in, COM9 appears. I know that COM9 is fine, but it would be very helpful if Windows can assign the next available COM to my device, which is COM3.
>
>Regards,
>Tan Teik Chuan
>
>From:??“Doron Holan”
>Reply-To:??“Windows System Software Devs Interest List”
>To:??“Windows System Software Devs Interest List”
>Subject:??RE: [ntdev] How Windows select which COM port to use
>Date:??Tue, 18 Apr 2006 08:04:11 -0700
> >I bet there are other virtual ports created on the machine or you have
> >moved your device from port to port on the usb hub.??COM9 is a fine
> >value.
> >
> >d
> >
> >– I can spell, I just can’t type.
>
>
>
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