Siemens SIMATIC NET PROFIBUS manual Configuration of optical line and star topologies

6 Configuration 6.1 Configuration of optical line and star topologies

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 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.

6.2 Configuration of redundant optical rings

The following configuration conditions must be fulfilled in the redundant optical ring (for details see Chap. 3.3 ”Redundant optical ring“, p.13):

(1) Configuration of a non-existent bus subscriber

(2) Increasing the retry value to at least 3

(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)

”Slot time“ is the monitoring period in bit times

 ”Length OF“ is the sum of all the optical fiber lines (segment lengths) in the network. The length must be given in km!

”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.

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