Siemens SIMATIC NET PROFIBUS Instructions d'exploitation télécharger pdf (Page 152)

100

101

Passive Components for RS-485 Networks

4-54

PROFIBUS Networks SIMATIC NET

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

Termination

The termination must be activated on the first and last node on the bus segment. If

termination is activated (termination on), the connection between the incoming (A1,

B1) and outgoing (A2, B20 segment is interrupted. The advantage of this is that if a

bus terminating resistor is activated incorrectly, the stations after the bus terminal

can no longer be accessed. When a segment is started up, you can then make

sure that no bus terminating resistors are activated that are not located at the

beginning or end of the network.

Note

Restriction when using the 12M bus terminal at 500 Kbps

This restriction only affects segments longer than 80 m.

If the 12M bus terminal is operated at a transmission rate of 500 Kbps along with

the RS-485 bus terminal with a 3.0 m tap line (6GK1 500-0AB00), a minimum

clearance of 5 m (= 5 m PROFIBUS cable) must be maintained between the

RS-485 bus terminal with the 3.0 m tap line. The 12M bus terminals can be

arranged at any point in the segment; in other words, no minimum clearance

needs to be maintained. The 12M bus terminal can also be included between two

RS-485 bus terminals with a 3.0 m tap line. The only important point in this respect

is that the PROFIBUS cable between the two RS-485 bus terminals with 3.0 m tap

lines must be a total of 5 m long.

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Siemens SIMATIC NET PROFIBUS Instructions d'exploitation Page 152

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