How can I set the power on default state of serial port on Windows 7?

4

How can I set the DTR line to high by default when a Windows 7 machine starts up?

Background: My own Windows service sets the condition of the com port lines to indicate its status. One of these is DTR high when in a startup state. However, since my service is set to delayed start, there is a period (2 mins, I think) when the DSR line is low after the machine is powered up, before my service starts and sets the DTR line to high.

Guy

Posted 2013-04-09T19:59:51.497

Reputation: 230

Answers

0

You choices are:

  1. Write code as a Device driver tagged BOOT_START which will load early but file system and other services would not necessarily be available.

  2. Tweak the order that your service starts see ServiceGroupOrder value in HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control and if you are booting from an SSD then your time will be reduced significantly.

Scott R

Posted 2013-04-09T19:59:51.497

Reputation: 115

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  • Pull up the external side of the DTR signal when the computer is switched on, and disconnect the pull-up resistor when the program is ready. Implementation details may be a little more involved.
    • < – Andrew Morton – 2016-03-27T10:20:12.070

    Asked: 2013-04-09T19:59:51.497

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    Active: 2016-03-27T10:41:09.710