User´s Guide Power Rail Booster
Version 12/2005
Copyright
©
Siemens AG 2005 All rights reserved.
6ES7 972-4AA02-0XA0
Page 23 of 49
5.3 Configuration of the Bus Parameters
Because of the way the PRB functions (see Chapter
3.2.4 „Signal regeneration“), the
network parameters for the DP master segment must be configured depending on
topology. This is done using the Hardware Configuration in STEP 7 or COM
PROFIBUS in STEP 5.
5.3.1 Configuring the Parameter: „Number of OLMs “
Fig. 13: Configuring the network parameters in Step 7´s Hardware Configuration
In the screen form shown above, the number of OLMs (Optical Link Modules) must
be entered on the “Fiber Optics” line. The following applies:
-
One OLM is equivalent to one PRB
-
The line length remains unchanged
The configuration tools then check to see whether the Slot Time parameter in the
selected communications profile can be left unchanged. If the slot time were to be
exceeded due to additional delays caused by Power Rail Boosters, a warning
message is issued and the parameters are modified accordingly.
The number of OLMs to be entered as the equivalent of the existing PRBs depends
on the selected topology. The minimum number of OLMs to be configured when
using PRBs is 2.
The following computational rule is applied to cascade configurations:
Number of OLMs = Number of PRBs connected in series
The delay level is:
T
v
(in Tbit) = 2 *Number of OLMs in series * 6Tbit
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