Applies To:
  • CitectSCADA
  • Windows NT
  • Windows 95

When running a TCP/IP Ethernet network with PLCs, Citect and network printers which use HP JetDirect cards and HP JetAdmin 2.33, it is possible to lose communications between Citect and the PLCs. The loss of communications is evident by periods of network dropouts - for a period of time the communications will operate correctly but then for no apparent reason communications will continually drop out for a period. This network communications dropout is also evident when using PLC programming software across the network.

If you put a network analyser on the network during the period of disrupted network communications, you may see a large sequential series of address resolution protocol messages (ARPs) being sent from the computer which is running the HP JetAdmin software.  

Download the latest version of HP JetAdmin (version 2.50 at the time of writing) from Hewlett-Packard's web site. Set your network printers with static IP addresses and then in the HP JetAdmin utility set the TCP/IP Discovery option to search for the specific IP addresses.

Further information on this problem can be found in Microsoft Technical Support Article ID: Q164609.