About Slave-to- Slave Messaging SCADA

Most SCADA half-duplex protocols do not allow one slave station to talk to another slave station, exept throught special application-soecific  code, which requires processing overhead in the master station. However, Allan-Bradleys DF1 half -duplex protocol implements slave-to-slave communications as a feature of the protocol within the master station, wirhout any additional application code or extra procesing overhead. Refer to chapter 3 of the DF1 Protocol and Commond Set Reference Manual, pulication 1770-RM516, for additional information.

If one slave station has a message to send to another, it simply includes the destination slave station's address in the message instrucrion's destination field in place of the master station's address when responding to a poll. The master starion checks the destination station address in every packet header it receives from any slave station. If the address does nt match its own station address, the entire message is forwarded back onto the telemetru network to the appropriate slave station, without any futrher processing.

Important: Slave stations using 1747-KE interfaces can respond to slave-tolslave messages but cannot initiate slave-to-slave messages

Image Source: http://scada.fultek.com


Retyped from: Book of SCADA System. Allen-Bradley. Rockwell Automation.Page 5.

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