Microsoft KB Archive/105308

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Windows NT May Cause APC Smart UPS Battery to Discharge

Article ID: 105308

Article Last Modified on 11/1/2006


  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Advanced Server 3.1

This article was previously published under Q105308


When Windows NT is booted, if an American Power Conversions (APC) Smart UPS is installed, its battery may be discharged or the UPS function may be shutdown.


During the boot sequence, Windows NT writes configuration/detection code to the COM Port to determine baud rate, FIFO information, and for mouse detection. The string written to the port may contain the letter "D," which the Smart UPS interprets as a command to discharge the battery. The string may also contain the letter "S," which will cause the Smart UPS to shutdown.

The Smart UPS interprets the string incorrectly only if it has already been placed in the "Smart Mode" prior to starting Windows NT. The user must have already placed the UPS in the Smart Mode using the software supplied by American Power Conversions; otherwise the Smart UPS will be unaffected by the signal Windows NT sends to the COM Ports.


The Smart UPS can be used successfully by temporarily disconnecting the cable from the COM Port during the Windows NT boot sequence. The user can also reset (power off, then on) the UPS to return to the default UPS mode. NOTE: This also has the effect of interrupting power to the computer.

American Power Conversions is currently working on a Windows NT driver that will take full advantage of the Smart UPS unit's capabilities.

The Smart UPS is manufactured by American Power Conversions, a vendor independent of Microsoft; we make no warranty, implied or otherwise, regarding this products' performance or reliability.

Additional query words: prodnt

Keywords: kbbug kbfix kbhardware KB105308