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Network variables can be used to exchange data between two PLCs. The variables must be defined in strict and identical lists on both PLCs which are sender and receiver. The lists can be in one or more projects.

A step-by-step description on how to use network variables can be found in the ‎⮫ application example.

The network variable list in the sender is a global variable list where specific log and transfer parameters are defined in their object properties. By adding these properties, you create a "network variable list (sender)" from an ordinary “GVL”. You can also insert a icon_nvl_sender “Network Variable List (Sender)” object directly into the device tree when this object already has these parameters set.

The network variable list in the receiver is of type icon_nvl_sender “Network Variable List (Receiver)”. When creating one, select the respective network variable list of the server. As an alternative, you can read this variable list from an export file that was generated from the sender list. An export file is required anyway for defining the sender list in another project.

The network variables are transmitted as broadcasting in one direction only: sender to receiver. However, it is also possible for a device to contain both sender and receiver lists. 

For the ‎NetVarUdp‎ library version 3.5.7.0 and later, a receiver channel is no longer assigned when confirmed transfer is not selected. In this way, network variable exchange is also possible between two controllers on one hardware device .

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  • If the exchanging devices should be senders and receivers, then the variable list identifiers must be unique in order to prevent abnormal operation. The variable list identifiers are defined in the “Properties” dialog of an object GVL.

  • Data exchange via network variables is not possible when:

    • The device (target system) does not support it.

    • A firewall blocks the communication.

    • Another client or application is using the UDP port that is set in the properties of the network variable list.

    • More than one application per sender device and receiver device use network variable lists.

  • Only arrays that have limits defined with a literal or constant are transmitted to the receiver application. Constant expressions are not permitted for this purpose.

    Example: "‎arrVar : ARRAY[0..g_iArraySize-1] OF INT ;‎" is not transmitted, but "‎arrVar : ARRAY[0..10] OF INT ;‎" is transmitted.

  • The maximum size of a network variable is 255 bytes. The possible number of network variables is unlimited.

  • If the size of the GVL exceeds the maximum length of the network telegram, then the data is split into multiple telegrams. Depending on the configuration, this can result in data inconsistencies.