Supplement operating manual for DREHMO i-Matic actuators with integrated
MODBUS fieldbus interface
Wenden, 21.03.12
Page 3 of 18
Prepared by: Ste
1 Introduction
This document describes the expansion of modbus RTU functionality for i-Matic actuator.
2 Interface technology
2.1 Physical interface
The physical interface is in accordance to the MODBUS over Serial Line Specification & Implementation guide
that can be found on the following web site:
http://www.modbus.org/
The physical interfaces uses 2-wire RS485.
The following parameters are possible for the communication configuration:
Baud rates:
38400 bit/s
19200 bit/s
9600 bit/s
4800bit/s
2400bit/s
1200bit/s
600bit/s
300bit/s
The parity can be configured as follows:
parity none, with two stop bits,
parity even, with one stop bit,
parity odd, with one stop bit
The interface card has two separate 2-wire RS485 modbus channels. The baud rate and parity settings are
common for both channels. Each of the channels can be assigned an individual slave address in the range of
1 to 247 (different addresses are possible for test-purposes on a single master).
Broadcast messages are not supported.
In case of a redundant connection, the slave device decides itself about the channel priority. Only the
commands of the high priority channel are executed. For maintenance reasons there is a feedback bit for the
channel quality of each channel and a command bit to change the channel priority.
The physical connection is done on a separate interface board mounted in the compact plug. The shield of the
cables have to be fixed on the according strain relieves on this interface board. For each channel there exists
separate screw-terminals for the incoming and outgoing signals and a dipswitch for the optional termination of
the lines. Furthermore there are dipswitches for the shield connection of incoming or outgoing cables to
ground potential.
