How to disable the serial port during boot - XP

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VK5PJ
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How to disable the serial port during boot - XP

Post by VK5PJ » Sun Jan 03, 2010 3:19 am

Hello to you all,
some time ago a reference to information on how to stop the serial ports on an Win /XP system from being scanned during booting was sent around the place and I applied that remedy to my shack PC, which was great as it stopped my radio from being put into TX for a few seconds as the PC booted. I believe it had something to do with MODEM auto discovery?

Of course now I have reloaded my copy of Win/XP and can for the life of me not find the information on how to do this.

Can anyone help by pointing me to where this might be published, from memory it was a simple registry changed but thats about all I can remember.

Regards,
Peter, vk5pj

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Re: how to disable the serial port during boot - XP

Post by VK7XX » Sun Jan 03, 2010 6:22 am


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how to disable the serial port during boot - XP

Post by VK5PJ » Sun Jan 03, 2010 8:24 am

Thanks John,
that looks like the info but it did not work for me this time, will keep looking

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Re: how to disable the serial port during boot - XP

Post by VK3HZ » Sun Jan 03, 2010 2:57 pm

Hi Peter,

My understanding is that the issue originates in the search for a mouse (and, in some cases, other serial devices) when Windows is booting. Windows does this by toggling the DTR and RTS lines together. A serial mouse responds to this by sending an "M". Our problem is that the rig also responds, because PTT is triggered by DTR and/or RTS.

This Microsoft KB article describes a fix for Windows NT4 and earlier:
http://support.microsoft.com/kb/131976
For Win XP, the fix is much the same, except the switch has been renamed to /FASTDETECT[=COMx] for some reason known only to Microsoft.

However, this may not solve the problem, because the mouse driver itself may be looking for the mouse using the same technique. Depending on the brand of mouse, the fix may be different, but you probably need to look for a way of specifying a fixed mouse port and disabling the search.

Also, if you have other serial devices with special drivers, they may do the same thing. Temporarily disabling the device would tell you if that's the case.

So, have a look at this link:
http://support.microsoft.com/kb/283063/en-us
Note that this talks mainly about Win 2000, but also mentions Win XP.

At the end of the day, it may be easier to put a switch in the DTR/RTS lines to the rig control box :roll:

Regards,
Dave.

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Re: how to disable the serial port during boot - XP

Post by VK5PJ » Mon Jan 04, 2010 3:38 pm

Ahh the tricky sods have two instances of the registry key that is shown in the article you sent the link for :evil:
VK5PJ wrote:Thanks John,
that looks like the info but it did not work for me this time, will keep looking
The real spot in the registry is HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\ACPI\PNP0501

At this location there are sub keys for each COM port you have on your machine and under these is the key "Device Parameters" and this is where you create the DWORD value called "SkipEnumerations" and set its value to be FFFFFFE (will check this when I get home)

Create a DWORD entry at - HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\ACPI\PNP0501\1\Device Parameters\ called "SkipEnumerations" and set its value to be FFFFFFE if you want to disbale scanning for COM 1

Do the same for COM 2 by changing the 1 to be a 2 in the string above

If this proves to be a bit much for anyone wanting to do this on an XP box, I can provide a small text file that will do the job for you.

Regards,
Peter Sumner

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Re: how to disable the serial port during boot - XP

Post by VK4DD » Tue Jan 05, 2010 4:06 pm

Hi Gents,

First I backed up my registery than I followed up the instructions from VK5PJ.
VK5PJ wrote:
Create a DWORD entry at - HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\ACPI\PNP0501\1\Device Parameters\ called "SkipEnumerations" and set its value to be FFFFFFE if you want to disbale scanning for COM 1
This registry edit works here with my XP :D
Only one click when I turn my computer on. But that is quite an improvement over the old situation.
I used to get upto 8 clicks during the boot section.

There are gone.... no more click clack click clack click claks during booting from the PC :wink:

I am using RTS to Key my rig. I don't use DTR.
I have only 1 com port and that is COM1.
Job done.

Thanks for the postings and for bringing up this topic.

73 Ron
VK4DD

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Re: how to disable the serial port during boot - XP

Post by VK5PJ » Sat Oct 18, 2014 7:13 am

Here we go again,
the move to USB based serial ports on my shack PC has seen all the rigs being pulsed to TX again when the PC boots (I have 3 interfaces running all the time).

Today I decided, dam I hate this and it was time to see if the fix for the real serial port (shown below in the quoted text) could be applied to a USB serial port
VK5PJ wrote:Ahh the tricky sods have two instances of the registry key that is shown in the article you sent the link for :evil:

The real spot in the registry is HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\ACPI\PNP0501

At this location there are sub keys for each COM port you have on your machine and under these is the key "Device Parameters" and this is where you create the DWORD value called "SkipEnumerations" and set its value to be FFFFFFE (will check this when I get home)

Create a DWORD entry at - HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\ACPI\PNP0501\1\Device Parameters\ called "SkipEnumerations" and set its value to be FFFFFFE if you want to disbale scanning for COM 1

Do the same for COM 2 by changing the 1 to be a 2 in the string above

If this proves to be a bit much for anyone wanting to do this on an XP box, I can provide a small text file that will do the job for you.

Regards,
Peter Sumner
Okay the answer is YES you can add the same registry key to a USB serial port and it will not pulse it during the boot phase of your PC.

In my case I use serial ports that have an FTDI chip / driver. in the Windows Registry these are all grouped under the "FTDIBUS" section and not the normal ACPI section for a hardware port

So for me its: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\FTDIBUS

Then there are some sub folders under there for each USB device you have plugged in, it is a bit of a fiddle to find and do but the results are quite good.

The easiest way to find the location is to use the search function in the Registry editor and look for the name of the com port.
eg. COM5 was one I have on my PC.

Regards,
Peter, vk5pj

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