[WriteLog] Transmit lockup when computer starts up

Floyd Sense sentek at sprintmail.com
Fri Apr 2 13:48:52 EST 2004

Yes, you're missing something.  This actually happened to me.  Everything
was turned on - I had been chasing DX - and I left the room for several
minutes.  While I was gone, we suffered one of the several daily power
glitches (Progress Energy customers will understand).  Windows rebooted,
scanned the COM ports, and raised the PTT line.  When I returned, things
were rather hot as the rig was key down with the amp on.  I've since
installed a UPS to get past the power failures, but there's simply no reason
to put up with this silly port scanning when it just isn't necessary.

Following is a description of the circumvention, including references to the
Microsoft website:

Fixing the Serial Port Windows Boot Problem

For as long as I can remember, I've lived with the problem of Windows
"diddling" the COM ports on my PC at boot time. My homebrew interface box
for RTTY, PSK and PC-generated-CW includes a "disable" switch to prevent
that activity from activating the rig's PTT and CW keying lines. Recently, I
picked up a RIGblaster Plus to use with my K2 and ran into a more serious
effect: Every now and then, when Win XP boots, the system "hangs" in the
middle of this scanning of the serial ports. The CW and PTT lines remain
activated and you either have a carrier on the air (if the rig is in CW
mode) or the rig is in transmit with the mic live (if in SSB mode). The
RIGblaster Plus offers no way to disable the serial interface other than to
remove power (no on/off switch) or disconnect the cables. After some
experimentation, I was able to prove that powering off the RIGblaster
prevented the hangs at boot time.

I decided to research the problem to see just why Windows was working with
the serial ports at boot time and if anything could be done to prevent it.
Windows scans the serial ports at boot time looking for new devices that
might have been added. That's how it identifies a device like a new modem
and therefore knows which drivers to load. (Windows documentation refers to
the activity as: Serial Device Enumeration). When devices are discovered,
Windows makes entries in the Registry containing information relating to the
ports and discovered devices. If you have serial ports dedicated to
radio-related interfaces that don't require special drivers, there's really
no benefit to this activity at all.

While searching for a solution, I discovered an item on the Microsoft
website titled: "Serenum: Serial Device Enumeration in Windows". This item,
dated May 22, 2002, explains the Serenum driver (used for serial ports) for
both Windows 2000 and Windows XP and details a way to disable the scanning
of individual serial ports. The technique involves locating the appropriate
Registry entries for the ports and adding a REG_DWORD value name,
"SkipEnumerations", in the Device Parameters key. The instructions on
finding the right Registry entries were a bit vague to me (not a Windows
expert!), but I finally located the right entries by searching the Registry
for the Com port number (Com2 in my case). The full path to the entry on my
system for my Com2 port is:

Device Parameters

The two path element names just before "Device Parameters" will undoubtedly
be different on your system. Remember- you have to make this change for each
serial port that you want to prevent the scanning for. After the change,
when the system is rebooted, the scanning of the ports that you added the
parameter for will not occur. The boot process will complete a bit faster
and you won't have to turn off your radio or interface to prevent problems.

If you're not comfortable editing the Windows Registry, this is probably not
the place to start! Find a friend who can help out. It would have been nice
if Microsoft had just given us a nice checkbox somewhere to control the
scanning function, but at least this solution works. If you want to give it
a try, search for "Serenum: Serial Device Enumeration" at www.microsoft.com
for complete instructions.

----- Original Message ----- 
From: "Chuck Dietz" <w5pr at swbell.net>
To: "'Floyd Sense'" <sentek at sprintmail.com>; <W7OM at aol.com>;
<writelog at contesting.com>
Sent: Friday, April 02, 2004 1:28 PM
Subject: RE: [WriteLog] Transmit lockup when computer starts up

> Could you just start the computer before turning on the transmitter?  Or
> I missing something?

More information about the WriteLog mailing list