Siemens SIMATIC NET 12M Operating Instructions Manual page 10

Introduction
1.2 Description of the product
Segment length and transmission speed
Transmission speed
9.6 - 187.6 kbps
500 kbps
1.5 Mbps
3 - 12 Mbps
Permitted segment lengths
Bus cable for PROFIBUS, standard type (see catalog IK PI).
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 used at a transmission rate of 500 kbps along with several RS-485
bus terminals with a spur line length of 3.0 m, a minimum distance of 5 m of PROFIBUS
cable must be maintained between two RS-485 bus terminals.
You can locate 12M bus terminals anywhere in the segment; there is no minimum distance
between them that needs to be kept to. You can also arrange a 12M bus terminal between
two RS-485 bus terminals with 3.0 m spur lines if you make sure that the PROFIBUS cable
between two RS-485 bus terminals has a total length of at least 5 m.
10
maximum segment length
800 m
400 m
200 m
100 m
Operating Instructions, 07/2013, C79000-G8976-C333-01
12M bus terminal