Microsoft KB Archive/108296

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Knowledge Base

9-to-25 Pin RAS Null Modem Cabling

Article ID: 108296

Article Last Modified on 10/31/2006


  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows NT Workstation 4.0 Developer Edition

This article was previously published under Q108296


The Windows NT Remote Access Help file includes tables showing the correct wiring of a null modem cable for use with RAS. The two tables included show the correct wiring for a 9-pin null modem cable and a 25-pin null modem cable. The following table contains the proper null modem wiring that must be used when the cable connects a 9-pin serial port to a 25-pin serial port.

   25-pin Connector       to    9-pin Connector
   2 (transmit data)      <->   2 (receive data)
   3 (receive data)       <->   3 (transmit data)
   4 (request to send)    <->   8 (clear to send)
   5 (clear to send)      <->   7 (request to send)
   6,8 (data send ready,
        carrier detect)   <->   4 (data terminal ready)
   7 (ground)             <->   5 (ground)
   20 (data terminal
       ready)             <->   6,1 (data send ready,
                                      carrier detect)

Additional query words: prodnt nul

Keywords: kbnetwork KB108296