Siemens SIMATIC NET PROFIBUS manual Configuring Redundant Optical Rings with OLMs

Configuring Networks

3.3.2Configuring Redundant Optical Rings with OLMs

The following configuration conditions must be satisfied in redundant optical rings:

1.Configuration of a Non-Existent Node

2.Raising the retry value to at least the value 3

3.Checking and adaptation of the slot time

To set the parameters under point 2. and 3., use the user-specific profile of the configuration tool. There is an example of adopting the bus parameters in STEP 7 at the end of this section.

Configuration of a Non-existent Node

The value of the HSA (Highest Station Address) parameter must be set on all DTEs so that there is at least one address in the network between bus address 0 and the value of HSA that is not used by a node; in other words, there is an address gap. You can obtain this address gap simply by increasing the value of the HSA parameter by one higher than the highest node address in the network.

Note

If this condition is not or is no longer satisfied, the optical bus will no longer close to form redundant optical ring following segmentation. The fault message (LED and signaling contact) of the two OLMs affected is not canceled even after the fault has been eliminated.

Raising the Retry Value to at Least the Value 3

If a fault occurs requiring a switchover to the redundant system (for example wire break), there is a switching time during which correct data transmission is not possible. To ensure a “bumpless” switchover for the application, it is advisable to set the number of frame retries on the PROFIBUS master to at least 3.

PROFIBUS Networks SIMATIC NET	3-27
6GK1970-5CA20-0AA1 Release 2 05/2000