Subscriber Variable

The properties that relate especially to a Subscriber Variable are defined on the configuration page of the Subscriber Variable (see next illustration). These properties include:

Variable Id
The Variable Id (=ProcessData ID) is the identification number of the Subscriber Variable. It can be changed online with the help of a PLC program if the option Online Changeable is marked.

DataType
Each Subscriber Variable has a version number (see version in chapter EAP telegram structure). The version number can be configured in “DataType Version”. It is verified before a Subscriber Variable is received (cf. network protocols section in Communication methods). The incoming ProcessData is discarded if the version numbers don't match. This verification is omitted if the option Ignore Version (once DataType Hash) is enabled.

Configuration settings for successful data exchange

In order to effect the exchange of data from a Publisher Variable to a Subscriber Variable, the configurations of the control computers involved must match each other. The section Network Protocol of the chapter Communication methods contains a description of the sequence of the reception of an EAP telegram or a Publisher Variable. In connection with the following aspects, it becomes clear how a data exchange is to be guaranteed:

• The destination address of the Publisher must be selected so that the EAP telegram reaches the addressee. Telegrams with Broadcast or Multicast addressing reach every network device. The exact destination address of the addressee must be configured for a Unicast telegram.
• As soon as the Any Publisher option has been selected in the Receiving Options of the receiver (Subscriber), each incoming EAP telegram is received and processed further, irrespective of its sender.
  An exception only occurs if
• a Multicast address is configured on the sender side that differs from the TwinCAT EAP Multicast MAC (01:01:04:05:00:00) and
• the destination address on the sender side (Publisher) does not match the configured Multicast MAC address on the Subscriber side.
• If a Publisher NetId is specified in the Receiving Options of the receiver (Subscriber), then only EAP telegrams coming from the specified sender (Publisher) are received and processed further.
• The ID of the Publisher Variable and that of the Subscriber Variable must be identical and unique in the network. If the ID of a sent Publisher Variable does not match the ID of a Subscriber Variable, the variable is discarded when it is received.
• The version (the hash) of the Publisher Variable and the associated Subscriber Variable must match. A sent PublisherVariable whose Version does not match the Version of a Subscriber Variable is discarded during reception unless the Ignore Data Type Hash option is activated in the receiver (Subscriber).
• The raw data length of a Publisher Variable must match the expected raw data length of the Subscriber Variable. The Publisher Variable will otherwise be discarded during the reception.