Modbus Rtu Protocol; Bacnet Ms/Tp - Siemens G120P Manual

3.7.3
3.7.3.1
3.7.3.2
3.7.4
Siemens AG

Modbus RTU protocol

Overview
The Modbus protocol is a communication protocol with linear topology based on a
master/slave architecture. In the Modbus RTU (Remote Terminal Unit), the data
are transferred in binary format and the data throughput is greater than in ASCII
code.
The Control Unit supports Modbus RTU as a slave with even parity.
1 bit
Start
Basic settings
Parameter Description
p0015 Macro drive unit
During the basic commissioning, select the value 109 "Modbus RTU", or with

firmware < 4.6 the value 21.
p2030 Fieldbus protocol selection (only with firmware < 4.6)
2: Modbus

p2021 Valid Modbus RTU addresses: 1...247
Invalid Modbus RTU address: 0
p2020 Fieldbus baud rate
 Baud rates from 4800 bps to 187500 bps can be set for communication.
 Factory setting: 19200 bps
p2024 Modbus timing
Index 0: Maximum slave telegram processing time

Maximum response time from the slave to the master.
 Index 1: Character delay time
Maximum permissible delay time between the individual characters in the Modbus
frame (Modbus standard processing time for 1.5 bytes).
Index2: Inter-telegram delay

Maximum permissible delay time between Modbus telegrams (Modbus standard
processing time for 3.5 bytes).
p2029 Fieldbus error statistics
Displays receive errors on the fieldbus interface.

p2040 Process data monitoring time [ms]
 Setting the time to monitor the process data received. If no process data is
received within this time, an appropriate message is output
Factory setting: 100 ms

 The setting 0 ms deactivates the monitoring.

BACnet MS/TP

In BACnet, components and systems are considered to be black boxes which
contain a number of objects. BACnet objects only define behavior outside the
device. Internal functions are not determined by BACnet.
Each component is represented by a series of object types and their instances.
8-bit data 1 bit
Parity even
Commissioning
3
Communication
1 bit
Stop
33
CM2G5111en
2014-05-16