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Siemens SIMATIC NET PROFIBUS User Manual

Page 96

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Configuring Networks

3-30

PROFIBUS Networks SIMATIC NET

6GK1970-5CA20-0AA1 Release 2 05/2000

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 t

Bit

6 Mbps

2000 t

Bit

3 Mbps

1000 t

Bit

1.5 Mbps

530 t

Bit

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.

3.3.3

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:

S

20 OLM G12 modules in the redundant optical ring

S

20 km total ring length

S

Transmission Rate 1.5 Mbps

S

Nodes attached directly to OLMs

S

“PROFIBUS-DP” bus protocol