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Serial Port Problems

Last response: in Windows XP
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June 16, 2005 8:15:04 PM

Archived from groups: microsoft.public.windowsxp.general (More info?)

I am having the following problem with my serial port (COM1), and it seems to
be windows (XP Professional) related:

I think Windows is controlling the DTR (pin4) and RTS (pin7) signals from
COM1. Instead of these pins being user controlable, windows seems to be
setting and holding them both active (+6V). On normal ports both signals are
negative (-5V). I think it is a Windows (and not hardware/bios) problem
because in bios mode (i.e. before windows boots up) both these pins are -5V,
however once windows starts up it controlls these pins makinging them +6V.
Curiously, when the computer wakes up from standby/hybernation both pins go
to -5V, however as soon as anything tries to access the port, both pins
return to +6V.

Has anyone else experianced this problem?? What is controlling these pins??
Is it a resource conflict?? How do i make XP Pro leave my serial port alone
to let other software control it??
This is driving me nuts, so all help/suggestions are greatly appreciated.

Thanks in advance,
Michael
--
Michael

More about : serial port problems

Anonymous
June 17, 2005 12:10:46 AM

Archived from groups: microsoft.public.windowsxp.general (More info?)

> Has anyone else experianced this problem?? What is controlling these
> pins??
> Is it a resource conflict?? How do i make XP Pro leave my serial port
> alone
> to let other software control it??
> This is driving me nuts, so all help/suggestions are greatly appreciated.


Michael,

Have you tried Jan Axelson's serial port website?
http://www.lvr.com/serport.htm

She has lots of excellent resources.

Steve
Anonymous
June 17, 2005 1:14:12 PM

Archived from groups: microsoft.public.windowsxp.general (More info?)

Please don't multi-post. See replies in hardware.

Michael wrote:

> I am having the following problem with my serial port (COM1), and it seems to
> be windows (XP Professional) related:
>
> I think Windows is controlling the DTR (pin4) and RTS (pin7) signals from
> COM1. Instead of these pins being user controlable, windows seems to be
> setting and holding them both active (+6V). On normal ports both signals are
> negative (-5V). I think it is a Windows (and not hardware/bios) problem
> because in bios mode (i.e. before windows boots up) both these pins are -5V,
> however once windows starts up it controlls these pins makinging them +6V.
> Curiously, when the computer wakes up from standby/hybernation both pins go
> to -5V, however as soon as anything tries to access the port, both pins
> return to +6V.
>
> Has anyone else experianced this problem?? What is controlling these pins??
> Is it a resource conflict?? How do i make XP Pro leave my serial port alone
> to let other software control it??
> This is driving me nuts, so all help/suggestions are greatly appreciated.
>
> Thanks in advance,
> Michael
!