Siemens SIPROTEC Manual page 17

BACKUP
Redundant slave
SIPROTEC PROFIBUS DP - Bus mapping 6MD662/3/4
C53000-L1840-B011-03
In the BACKUP subsystem, the master device behaves passive in process direction.
Only read access of process data is possible for the BACKUP master.
All data in the output messages are rejected by the BACKUP slave interface.
A Master-Master communication
master devices and for mutual supervision.
In case of a failure of components in the current PRIMARY subsystem, the BACKUP
system can take process control and become PRIMARY for its part (redundancy
switchover).
A redundant PROFIBUS DP slave (e.g. 6MD663 or 6MD664) which can be connected
to the system-redundant communication as shown in Figure 1-2 has the following
characteristics:
• The redundant slave consists of two independent PROFIBUS communication inter-
faces (which are redundant with respect to the protocol firmware and the hardware
interface).
• It exists an internal communication channel (independent from PROFIBUS)
between the two PROFIBUS communication interfaces of the redundant slave.
This communication channel is described as RedCom subsequently and serves for
exchanging of status information as well as for mutual supervision.
• Both slave interfaces have identical PROFIBUS addresses.
• One of the both slave interfaces works as PRIMARY, the other as BACKUP.
Output data of the master device are only evaluated in PRIMARY state.
The decision if a slave interface can become PRIMARY depends on various factors:
• Communication status with the master device ("in data exchange" or "not con-
nected").
• PRIMARY/BACKUP state of the master device.
The master device must inform the slave about its state via PROFIBUS communi-
cation. In the implementation of the redundant slave of the SIPROTEC devices a
byte in the data area of the cyclic data exchange message is used for that (ref. to
chap. 1.4.1.4).
• Operating status of the partner module (partner interface) in the redundant slave.
This contains both the current redundancy state (PRIMARY/BACKUP) and the
hardware state ("operational" or "error").
RedCom communication is used to determine the state of the partner module.
The behavior of the redundant slave of the SIPROTEC devices in case of redundancy
start-up and redundancy switchover is described in chap. 1.6.
1. An arbitrary communication connection between the master devices.
Also a superordinated control system can do this task.
Redundant PROFIBUS DP interface
1
servers for comparison of the process images in the
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