Siemens SIMATIC NET PROFIBUS manual Example of Configuring the Bus Parameters in Step

Configuring Networks

Note

The slot time calculation takes into account only the optical network and the attachment of nodes to the OLM in each case via a maximum 20 m long RS-485 bus segment. Longer RS-485 bus segments must be included by adding them to the length FOC.

With the OLM/G11-1300 and OLM/G12-1300, the minimum slot times shown in the following table must be maintained at transmission rates of 12 Mbps, 6 Mbps, 3 Mbps and 1.5 Mbps.

Table 3-11 Minimum Slot Time for

OLM/G11-1300 and OLM/G12-1300

Transmission rate		Minimum slot
		time
12	Mbps	3800 tBit
6	Mbps	2000 tBit
3	Mbps	1000 tBit
1.5	Mbps	530 tBit

When configuring the slot time, use the minimum slot time as shown in Table 3-11 if the calculated slot time is less than the minimum slot time.

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.

3.3.3Example of Configuring the Bus Parameters in STEP 7

Structure of the Network Example

The example assumes a redundant optical ring with the following structure:

S20 OLM G12 modules in the redundant optical ring

S20 km total ring length

STransmission Rate 1.5 Mbps

SNodes attached directly to OLMs

S“PROFIBUS-DP” bus protocol

3-30	PROFIBUS Networks SIMATIC NET
	6GK1970-5CA20-0AA1 Release 2 05/2000