8
PKE-COM-RTU Modbus RTU communication interface for PKE12/32/65
03/20 MN034005EN
2 Modbus RTU
2.1 General
Modbus is a centrally polled bus system in which a so-called master (PLC) controls the
entire data transfer on the bus. Internode communication between the individual modules
(slaves) is not possible.
Every single data transfer operation is initiated by the master with a request. Only one
request can be sent on the cable at a time. Slaves are not able to initiate transfers, and
are only able to respond to requests.
Two types of dialog are possible between master and slave:
•
The master sends a request to a slave and waits for a response.
•
The master sends a request to all slaves and does not wait for a response (broadcast).
More information on the topic can be found at
www.modbus.org.
2.2 Communication
Figure 2: Modbus line with PKE
Figure 2 shows a typical setup with a host computer (master) and any number (a
maximum of 63 modules) of PKE (slaves). Each PKE has a unique address on
the network.
Addressing is performed individually for each PKE via the DIP switches on the respective
PKE-COM-RTU module. It is independent of the physical connection (position) in
the network.
A bus termination resistor is required at the last module on the Modbus line.
. . .
HMI-PLC
Modbus RTU
24 V DC
1
2
63
2.1 General
2 Modbus RTU