Siemens Sinamics S120 Function Manual page 597

Master and slave
● Master and slave properties
Table 10- 54 Master and slave properties
As bus node
Send messages
Receive messages
● Master
● Slaves
Bus access method
PROFIBUS uses the token passing method, i.e. the active stations (masters) are arranged in
a logical ring in which the authorization to send is received within a defined time frame.
Within this time frame, the master with authorization to send can communicate with other
masters or handle communication with the assigned slaves in a master/slave procedure.
PROFIBUS telegram for cyclic data transmission and acyclic services
Each drive unit that supports cyclic process data exchange uses a telegram to send and
receive all the process data. A separate telegram is sent in order to perform all the acyclic
services (read/write parameters) under a single PROFIBUS address. The acyclic data is
transmitted with a lower priority after cyclic data transmission.
The overall length of the telegram increases with the number of drive objects that are
involved in exchanging process data.
Drive functions
Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
Properties
Masters are categorized into the following classes:
– Master class 1 (DPMC1):
Central automation stations that exchange data with the slaves in cyclic and acyclic
mode. Communication between the masters is also possible.
Examples: SIMATIC S7, SIMOTION
– Master class 2 (DPMC2):
Devices for configuration, commissioning, operator control and monitoring during bus
operation. Devices that only exchange data with the slaves in acyclic mode.
Examples: Programming devices, human machine interfaces
With respect to PROFIBUS, the SINAMICS drive unit is a slave.
10.2 Communication via PROFIBUS DP
Master
Active
Permitted without external
request
Possible without any restrictions Only receive and acknowledge
Communication
Slave
Passive
Only possible on request by
master
permitted
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