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eWON wiki > eWON Support > Knowledge Base > Questions and Answers > Store and Forward tags

Store and Forward tags

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What we call store&forward is the ability of the eWON to read a value from one protocol and to write this value on another protocol.
It's like a "protocol converter" but with limitations.

For example, I want my S7-300 (with ethernet port) reads a temperature from a ModbusRTU device.
We can do that by placing an eWON (an eWON500 is enough) between the Siemens and the Modbus device.

In the eWON:

Define a "reading tag" on the Modbus device.

StoreAndForward01.png
 

Define a "writing tag" on the S7 device.

StoreAndForward02.png
 

Write a little BASIC script to assign the value read in the Tag to write.

 

Here, you have several strategies to do this copy:

  1. On timer:
    At a specified interval, you'll copy the value from one tag to the other.

    Init section:
    Ontimer 1,"goto TagsCopy"
Tset 1,30

    Timer section:
    TagsCopy:
  S7Temperature@ = MbsTemperature@
END

     
  2. On change:
    Only when the read value will change, you'll copy the value from one tag to the other.

    Init section:
    Onchange "MbsTemperature","S7Temperature@ = MbsTemperature@"