Siemens SIMATIC NET PROFIBUS, Owner'S Manual, Page: 72 / 490

Configuring Networks
3-6
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Rules
At a transmission rate of 1.5 Mbps, the following rules apply to the permitted
number of nodes and their distribution/layout on a SIMATIC NET PROFIBUS
segment:
1. The maximum permitted number of nodes on any segment is 32.
2. The sum of the values of all the connection elements in a segment must be
≤
25.
3. The rules for the distance between adjacent connection elements are as follows
(distance in this case is the length of the LAN cable):
3.1 If the distance between adjacent connection elements is greater than
10 m, the values of the connection elements can be ignored.
3.2 If the distance between adjacent connections elements is greater than the
sum of the two values of the elements in meters, the layout is not
critical and no additional conditions need to be taken into account.
The value of the PG connecting cable, SIMATIC S5/S7 connecting cable
12 Mbps must be added to the value of the corresponding
connection element.
3.3 If the minimum clearance described in 3.2 is not kept to, this results in
a group being formed and the following additional conditions must be met:
– Attachment elements can be arranged as close to each other as
required providing the sum of their values does not exceed the value 5.
– The distance in meters between two adjacent groups must be at least
as large as the sum of the values of the two groups
.