Transmission Technique/Physical Layer; Protection Functions / Data Secure Mechanisms - Drehmo i-matic Operating Manual

2.3 Transmission technique/Physical layer

Data is transmitted by means of a physical connection over a twisted pair two wire cable. The
interface board supports transmission rates up to 115200 Baud.
Bus access is handled in master/slave mode. Only one master can be active at a time (Mono
master mode). The master acts with polling mode and a request / response cycle.
In one master system theoretically 247 slaves can be addressed.
The used protocol is MODBUS RTU.

2.4 Protection functions / Data secure mechanisms

As protection mechanisms against data violation MODBUS RTU implements a parity check for
each byte and a 16 bit CRC for every MODBUS telegram.
In addition a watchdog within the slaves monitors the correct connection to the master. The
behavior of the actuator as well as the timeout value is parameterizable .
The master should also implement a communication monitoring resulting in a failure signalization
in case of communication loss or malfunction.
DREHMO – i-matic Modbus loop redundant board page 7 of 32
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