Profibus DP Mk2 Option Card Installation Manual
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Publication PUB088-005-00_1017
4.3.1
Flying Redundancy Slave to Master Connection
With FR (Flying Redundancy) the aim is to protect against a failure of the Profibus Interface. The data
highway is considered to be more reliable than the connection interface. There is a single data
highway and both the Profibus card inputs are connected to it. The card must be set to FR mode and it
then adopts a fixed offset of 64 between the set address (used for primary communication) and the
backup communication address.
When the card is powered ‘on’, Channel 1 will be the Primary channel. If the card does not enter
Configuration Mode within 1 second (because there is no Master present) then Channel 2 will take
over as Primary. Once again, if there is no communication within 1 second, then it will revert to
Channel 1 and now it will wait 2 seconds before Channel 2 assumes Primary status. The switch over
time will increase by a factor of 2 each time until it reaches its maximum of 32 seconds. It will continue
to switch channels using a 32 second switch over time until one channel receives PLC messages.
In the event of a failure of the Primary channel, the Backup automatically changes to use the Primary
address. Hence for all control purposes the Master only uses the Primary address. The Backup
address can be used for exchanging data but any commands to move the actuator directed to the
backup address will be ignored. If a configuration message is sent to the Backup address that is
different to the one sent to the Primary address it will be accepted, but not actioned. The data
exchanged between the Master and the Primary includes information on the status of the device and
hence the availability of a Backup should the Primary fail.
Single Data Highway, two communication ports
Channel 1 is Primary on power up
Default method is SR mode; to achieve FR parameter 15 must be altered
Fixed offset of 64 between Primary and Backup addresses
Backup automatically adopts Primary address if Primary fails
V0 cyclic Commands to Backup ignored
Reports the status of Primary and Backup to the Master
Configuration and Parameterisation changes only over the Primary address
Fig 15: Profibus DP (Mk2) Flying Redundancy Connection
Backup Master
Primary Master
Primary
Backup
Slave
n
64+n
FR
