Technical data

Network configuration
3.3 Frame transmission time
PROFIBUS Network Manual
System Manual, Edition 04/2009, C79000-G8976-C124-03
65
If the slot time is lower than the minimum slot time, use the minimum slot time according the
table above for the slot time you are configuring.
Note
If the slot time is configured with a value that is too low, this can lead to malfunctions and
error displays on the OLM. The system LED flashes red/green.
3.3.4 Example of configuring the bus parameters in STEP 7
Structure of the network example
The example assumes a redundant optical ring with the following structure:
● 20 OLM G12 modules in the redundant optical ring
● 20 km total ring length
● Transmission speed 1.5 Mbps
● Nodes attached directly to OLMs
● "PROFIBUSDP" bus protocol
Calculating the slot time
For the transmission speed of 1.5 Mbps selected in the example, Section "Cable lengths for
plastic and PCF FO links (Page
52)" lists the following values
a = 351
b = 30
c = 24
From this, the slot time is calculated as follows:
Slot time = 351 + (30 x 20) + (24 x 20) = 1431
Entering the bus parameters
This means that the following 3 bus parameters must be entered for the example:
Slot time (T_slot_Init) = 1431
Number of retries (Retry_Limit) = 3
Highest station address (HSA) = 126 (default setting)
These values are entered in STEP 7 in the "Bus Parameters" dialog for the "UserDefined"
bus profile.