Emerson Bettis XTE3000 Installation, Operation And Maintenance Manual page 14

Section 6: Slave Redundancy (DP-V2)
March 2022
The PROFIBUS DP communication with a redundant slave will be done in the following way:
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At the start up (and every time it is necessary), the Master sends the PRM commands to two slave
interface cards in order to determine which is the Primary and the Backup.
The Primary slave sends the complete diagnosis information of the Redundant slave.
The monitoring of the PROFIBUS communication ability of the Redundant slave is done by the
redundancy of the master with standard PROFIBUS mechanisms. Therefore, all communication parts
of the Backup slave shall be fully operable. They shall be connected to the bus, the driver shall be
enabled, and the PROFIBUS ASIC is initialized and running.
If the master redundancy detects a communication failure to the Primary slave, it will issue a
command to the Redundant slave to inform it about that fact. The Redundant slave performs a
redundancy switchover.
The monitoring of the PROFIBUS communication by the master will work also for a single line failure.
That means, when only the receive-line or the transmit-line of the Primary slave has a failure, the
Master will also detect this and the command will be sent to the Redundant slave.
One of the key features of the Slave redundancy is that the process input and output signals are stable
during a redundancy switchover. From the process point of view, a redundancy switchover is invisible.
The master or the master application is responsible to keep the input signals of a Redundant slave
stable during the switchover.
The hardware implementation of the Slave Redundancy for the PROFI2000v4 is shown in Figure 7.
Figure 7
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MS0 (cyclic): The primary slave uses the cyclic communication to send and receive the
process values. In addition, the primary slave sends all diagnosis information about itself
and the backup slave.
The backup slave also sends and receives data with the MS0 services, but these data is not
relevant and shall be ignored by the backup slave and the master.
MS1 (acyclic): Only the primary slave receives and transmits MS1 services.
When the backup slave receives a MS1 service, it responds negative.
MS2 (acyclic): Both the primary and the backup slave receive acyclic MS2 services. Both
slave interface cards process these services to allow an individual communication with the
specific device.
PROFIBUS
RS485
Transceiver
PROFIBUS
ASIC
microcontroller
Red extensions
Internal comm.
channel
Internal comm.
channel
Installation, Operation and Maintenance Manual
PROFIBUS
PROFIBUS
RS485
Transceiver
PROFIBUS
ASIC
microcontroller
Red extensions
Internal comm.
channel
Internal comm.
channel
Actuator
base card
MDE 256 Rev. 1
Slave Redundancy (DP-V2)