Network Communication Via The Integrated Modbus; Interface; Protocol Description - ABB 07CR41 Operating Manual

6.2 Network communication via the integrated MODBUS

6.2.1 Protocol description

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Communication
Communication is of greater importance in wide area installations. The AC31 system features
other interfaces in addition to the CS31 system bus, in order to support different
communication modes.
This chapter provides a detailed description of the interfaces available with the 40 and 50
series basic units which support three communications protocols on the same serial interface
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(Figure 3). The MODBUS
three for communicating with other devices.
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The MODBUS protocol is used worldwide. The MODICON MODBUS
integrated in the 40 and 50 series basic units.
Numerous automation devices such as PLCs, displays, frequency converters or monitoring
systems feature by default, or as an option, a MODBUS
easily communicate with the 40 or 50 basic units via the serial interface (RS232 or RS485).
Figures 4, 5 and 6 show three configuration examples:
Point to point connection with a PC (Figure 4)
Network connection with a PC (Figure 5)
Network connection between basic units (Figure 6)
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MODBUS is a question/answer protocol that is still occasionally referred to as master/slave:
the master sends a request to the slave and waits for the slave's reply.
The master devices on a MODBUS
systems. The slaves on the MODBUS
Description of the MODBUS
Available on
Mode
Number of connection points
Protocol
Data transmission control
Speed
Maximum length
mode is the easiest and at the same time the most powerful of the
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network are generally basic units, displays or monitoring
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network are generally PLCs, frequency converter, etc.
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protocol:
RS-232, RS-485, optic fibers,...
RS485 half-duplex
1 master
max. 1 slave with RS232 interface
max. 31 slaves with RS485 interface
max. 255 slaves with bus amplifier
MODBUS
CRC 16
Up to 19,200 baud
On RS-485:
1,200 m at 19,200 baud
1,500 m at 300 baud
6 – 6
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interface

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RTU protocol was
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RTU interface and can therefore
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(master/slave)
Advant Controller AC 31 / Issued: 01.99