Communication Protocols - Bosch Rexroth EFC 3600 Operating Instructions Manual

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Communication Protocols

13 Communication Protocols
13.1 Brief Introduction
EFC 3600 frequency converters provide standard RS485 communication port to realize
the communication between the master station via ModBus protocol. With the help of a
PC, a PLC or an external computer a "single master/multiple slaves" network control
can be realized (setting of frequency control command and running frequency, modifi‐
cation of function code parameters, monitoring of frequency converter running status
and failure messages) to address the specific requirements of applications.
13.2 ModBus Protocol
13.2.1 Protocol Description
Brief introduction
● ModBus is a master/slave protocol. Only one device may send commands in the
network at a particular time.
● The master station manages information exchange by polling the slave stations. Un‐
less being approved by the master station, no slave station may send information. In
case of an error during data exchange, if no response is received, the master station
will query the slave stations absent from the polling.
● If a slave station is unable to understand a message from the master station, it will
send an exception response to the master station.
● Slave stations can't communicate with each other but through the master's software,
which reads data from one slave station and send them to another. There are two
types of dialogs between the master station and the slave stations:
– The master station sends a request to a slave station and waits for its response.
– The master station sends a request to all slave stations and does not wait for their
response (broadcasting).
Transmission
The transmission is of RTU (remote terminal unit) mode with frames containing no mes‐
sage header or end mark. A typical RTU frame format is shown below:
Slave address
1 byte
Fig.13-1: Typical RTU frame format
Data are transmitted in binary codes.
172/235
Function code
1 byte
DOK-RCON03-EFC-3600***-IT01-EN-P
Rexroth Frequency Converter EFC 3600
Data
0 ~ 252 byte(s)
CRC
CRC low|CRC high