Download DFE11B Ethernet - Fieldbus Interface

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5
Operating Characteristics of Modbus / TCP
Introduction
0
5
Operating Characteristics of Modbus / TCP
5.1
Introduction
Modbus / TCP is an open protocol based on TCP / IP. It has become established as the
standard solution for industrial Ethernet interface modules. Modbus / TCP uses port
502. The following service FCs (Function Codes) are available for process data
exchange, parameter data exchange and unit identification:
•
FC3 – Read Holding Registers
•
FC16 – Write Multiple Registers
•
FC23 – Read Write Multiple Registers
•
FC43 – MEI, Type 0x0E "Read Device identification"
A bus station is represented as a coherent register block via Modbus / TCP. The register
block can include up to 64 k words and is addressed from reference number (= offset) 0.
This register block contains the process data of the frequency inverter and a parameter
channel. Services FC3, FC16 and FC23 are suitable for the cyclical exchange of process data with the Modus master (client). We recommend you use service FC23. The
DFE11B option card can exchange up to ten process data words with the Modbus
master (client) (→ Sec. "Mapping").
Protocol
structure
Byte
Designation
Meaning
0
Transaction identifier
Often 0, is simply copied by the server (slave)
1
Transaction identifier
Often 0, is simply copied by the server (slave)
2
Protocol identifier
0
3
Protocol identifier
0
4
Length field (upper byte)
0
5
Length field (lower byte)
Number of following bytes
6
Unit identifier (slave address)
0 or FFhex
7
Function code
Required service, e.g. FC23
..
Data
Depends on the service
The transaction identifier is assigned by the master (client) and simply copied by the
slave (server). The protocol identifier must be zero. The length specifies the number of
following bytes. The unit identifier must be 0 or FFhex, which means that the DFE11B
end station is on the bus and does not function as a gateway. The required function code
is entered in byte 7. The data bytes after byte 8 depend on the function code selected.
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Manual – MOVIDRIVE® MDX61B Fieldbus Interface DFE11B Ethernet