Siemens SIMATIC NET PROFIBUS - Manual (Page 93)

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