Siemens SIMATIC NET PROFIBUS - Manual (Page 425)

6.1 Configuration of optical line and star topologies
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6 Configuration
Version 1.0 8/00
6 Configuration
During configuration, the PROFIBUS network parameter "Slot time" must be adapted to the network coverage,
network topology and the data rate due to frame delays caused by lines and network components, as well as by
monitoring mechanisms in the network components.
6.1 Configuration of optical line and star topologies
The following configuration conditions must be fulfilled in the redundant optical ring
(for details see Chap. 3.3 ”Redundant optical ring“, p.13):
Ⅲ
(1) Configuration of a non-existent bus subscriber
Ⅲ (2) Increasing the retry value to at least 3
Ⅲ
(3) Checking and adjusting the slot time
Use the user-specific profile of the configuration tool to set the parameters under (2) and (3).
Calculate the slot time with the following equation:
Slot time = a + (b
.
Length
OF
) + (c
.
Number
OLM
)
Ⅲ ”Slot time“ is the monitoring period in bit times
Ⅲ
”Length
OF
“ is the sum of all the optical fiber lines (segment lengths) in the network.
The length must be given in km!
Ⅲ
”Number
OLM
“ is the number of PROFIBUS OLMs in the network.
The factors a, b and c are dependent on the transmission rate and are listed in the tables below.
6.2 Configuration of redundant optical rings
The PROFIBUS network is configured, e.g. with SIMATIC STEP 7 (V5) or COM PROFIBUS (V5). The number of OLMs
(Number
OLM
) and overall line lengths can be entered in an input mask. The configuration tools control whether the
slot time in the selected communications profile can be retained. If this time is exceeded as a result of additional OLM
and optical fiber line runtimes, an error message is issued and the parameters are adapted accordingly.