Applies To:
  • CitectSCADA 5.xx
  • CitectHMI 5.xx

I am using the S7NT driver to talk to several Siemens S7 PLCs. When I put one of the PLCs offline (for example when I disconnect it from the PLC network) then all S7 I/O Devices in CitectHMI/SCADA go offline. 

You have probably defined only one VFD name for all your I/O Devices that use the S7NT or S7WIN protocol. In that case CitectHMI/SCADA will no longer be able to reach any of the defined I/O Devices, when one I/O Device that uses that specific VFD name goes offline.

The S7NT driver requires a unique VFD name per I/O Device.

A VFD name is a so called Virtual Field Device name that is defined in the Simatic Net software from Siemens. This name is used by the S7 API, (contained in the S732.dll), when communicating to S7 PLCs. The Citect S7NT driver actually only talks to the S7 API, and the S7 API on its turn talks to the actual S7 PLCs via either an Ethernet, Profibus DP or MPI connection.

In CitectHMI/SCADA the VFD name is used in the special options field in the Ports form. So you need to define one port for each I/O Device, when using the S7NT or S7WIN driver.