ABB 07AC91, Руководство по эксплуатации

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Communication 6 – 6
Advant Controller AC 31 / Issued: 01.99
3
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
(Figure 3). The MODBUS
®
mode is the easiest and at the same time the most powerful of the
three for communicating with other devices.
6.2 Network communication via the integrated MODBUS
®
interface
6.2.1 Protocol description
The MODBUS
®
protocol is used worldwide. The MODICON MODBUS
®
RTU protocol was
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
®
RTU interface and can therefore
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)
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
®
network are generally basic units, displays or monitoring
systems. The slaves on the MODBUS
®
network are generally PLCs, frequency converter, etc.
Description of the MODBUS
®
protocol:
Available on
RS-232, RS-485, optic fibers,...
Mode RS485 half-duplex
Number of connection points 1 master
max. 1 slave with RS232 interface
max. 31 slaves with RS485 interface
max. 255 slaves with bus amplifier
Protocol
MODBUS
®
(master/slave)
Data transmission control
CRC 16
Speed Up to 19,200 baud
Maximum length On RS-485:
1,200 m at 19,200 baud
1,500 m at 300 baud