ABBAC 800M PROFIBUS DP Configuration

• PROFIBUS master unit CI854A

• PROFIBUS slave unit

• PROFIBUS line.

Depending on your needs each type of redundancy can be configured independent 

of each other. Also mixed configurations are supported. You can configure for 

example a redundant PROFIBUS installation consisting of a redundant CI854A 

master unit and redundant PROFIBUS lines and have connected redundant and nonredundant slave units in parallel. 

A special mixture of redundancy is the so called combined slave and line 

redundancy. A slave provides two slave units supporting the PNO slave redundancy 

and each slave unit only provides one PROFIBUS interface. This is a one error 

tolerant solution. The slave unit will only have communication on one PROFIBUS 

line at a time and a single error on the PROFIBUS line will lead to a switchover of 

the slave units. But the big advantage of this solution are the reduced cost. Therefore 

it is a very popular solution. It is used for example for S800 I/O with CI840 and 

S900 I/O with CI920.

Master Redundancy

The CI854A supports PROFIBUS master redundancy. Two CI854A connected to 

one controller can be configured to work in a redundant configuration. The 

configuration for redundancy is done via configuring the CI854A in the hardware 

tree of the Project Explorer. For configuration of redundancy please refer to Add 

Redundancy for Master Unit on page 41.

Primary and backup CI854A need different node addresses on PROFIBUS. While 

the primary node address is configured via the settings in the HW Configuration 

Editor the node address for the backup module is defined by the fixed offset -1 to the 

node address of the primary module. Therefore you cannot configure the node 

address 0 on PROFIBUS with CI854/CI854A. This is reserved for redundancy.

During normal operation only the primary CI854A has communication with the 

slave units. The backup unit is in hotstandby mode. It is configured by the controller 

and synchronized by the primary unit. If there is a failover because of for example a 

disturbed PROFIBUS communication, primary and backup module change the node 

addresses. During failover the former primary module will get reset. 

After download and successful configuration the availability of the backup unit is 

monitored. This includes the balancing of current data and the communication links 

via PROFIBUS and CEX-Bus as well. In case of no error the DUAL LEDs on 

primary and backup unit will be lit. If the backup unit is not ready to takeover the 

DUAL LEDs will get off on both units. The error will be indicated in the unit status 

and a potential redundancy switchover will be inhibited in this case. 

Reasons to perform a switchover are for example that the primary unit has lost the 

communication to all connected slaves “All slaves failed” because of for example a 

cabling problems or a “Fatal error” on the primary CI854A itself was detected. 

Slave Redundancy

The CI854/CI854A supports the PROFIBUS slave redundancy like specified by the 

PROFIBUS User Organization (PNO). The specification can be found at 

http://www.profibus.com. 

A redundant slave has two PROFIBUS interfaces, one for the primary and one for 

the backup slave. If line redundancy is used, one of the interfaces is connected to 

line A and the other to line B. If not, both interfaces are connected to the same 

PROFIBUS cable. The PROFIBUS address of the backup slave is always the 

address of the primary slave plus 64. The configuration in the Control Builder 

ensures, that both addresses are available when the slave is set redundant. If a 

redundancy switchover of a slave occurs, also the PROFIBUS addresses are 

switched. That means, the primary slave always has the assigned address and the 

backup slave always has the address + 64 regardless of who is the primary and who 

is the backup. This kind of redundancy is called "flying redundancy". 

Only the primary slave can transfer process data and diagnostic information on the 

PROFIBUS. Therefore the status of the primary slave also contains the information 

of the backup slave. Please refer to the slave documentation for the details.

Although the backup slave has no active data transmission with the master the 

CI854/CI854A is able to monitor the backup slave. The backup slave is available in 

the Livelist and if redundancy is configured the monitoring will be activated. If the 

backup slave fails, the information "Redundant slave does not exist" will be set in 

the ExtendedStatus of the primary slave.

To allow the slave a failover in case of an error the CI854/CI854A has a special 

monitoring function. If the redundant slave gets disturbed the CI854/CI854A waits 

for (2* watchdog time + 1) before connection down will be indicated for the slave. 

During this time the slave can perform a switchover and proceed with the normal 

data exchange without interrupting the communication.