Introduction and overview
1.2 Bus systems
3WL/3VL circuit breakers with communication capability - PROFIBUS
System Manual, 03/2011, A5E01051353-02
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This access procedure is called CSMA/CD. This "random" access procedure cannot
guarantee that a reply is sent within a specific time period. That depends heavily on the bus
traffic load. For this reason, it is not possible to implement real-time applications with
Ethernet.
Data transfer
There are several methods of transferring the data of the SENTRON circuit breakers on
PROFIBUS DP to Ethernet. These are represented here by two solutions using SIEMENS
components:
Solution 1 A SIMATIC S7 controller is equipped with a PROFIBUS DP interface
(CPU-internal interface or modules with communications processors) and
an Ethernet interface. The data transferred by the circuit breakers over
PROFIBUS DP is "re-sorted" in the SIMATIC and communicated via
Ethernet. The CP 343-1, CP 343-1 IT, CP 343-1 PN, CP 443-1 and
CP 443-1 IT are available as possible Ethernet communications
processors for the S7.
Solution 2 As an autonomous component, the IE/PB link forms the seamless
transition between Industrial Ethernet and PROFIBUS DP.
Ordering information
Ordering information and further gateway options can be found in the Catalog "Industrial
Communication" (IK PI) Chapter 8.
1.2.3 Modbus RTU
Definition/standard
Modbus RTU is an open, serial communication protocol based on the master-slave
architecture. It can be implemented extremely easily on any serial interfaces. Modbus
comprises one master and several slaves, with communication controlled exclusively by the
master.
Communication
Modbus RTU has two fundamental communication mechanisms:
● Query/response (Polling): The master sends a request frame to any station and expects a
response frame.
● Broadcast: The master sends a command to all stations on the network. These execute
the command without acknowledgment.
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