Siemens Automation System S7-400 - Manual (Page 113)

Networking
5-15
Automation System S7-400 Hardware and Installation
A5E00850741-01
5.4 Cable Lengths
Segment in the MPI Network
In a segment of an MPI network, you can use cable lengths of up to 50 m. This
50 m applies from the first node to the last node in the segment.
Table 5-1 Permitted Cable Length of a Segment in an MPI Network
Transmission Rate Maximum Cable Length of a Segment (in m)
187.5 Kbps 50
19.2 Kbps 50
12 Mbps 50
Segment in the PROFIBUS-DP Network
In a segment of a PROFIBUS-DP network, the cable length depends on the
transmission rate (see Table 5-2). These lengths only apply if you connect a CPU
to a PROFIBUS-DP network via an MPI interface configured as a DP interface.
Table 5-2 Permitted Cable Length of a Segment in the PROFIBUS-DP Network
Depending on the Transmisson Rate
Transmission Rate Maximum Cable Length of a Segment (in m)
9.6 to 187.5 Kbps 1000
500 Kbps 400
1.5 Mbps 200
3 to 12 Mbps 100
Longer Cable Lengths
If you have to implement cable lengths which are longer than permissible in one
segment, you must interconnect RS 485 repeaters. The maximum possible cable
length between two RS 485 repeaters is the same as the cable length of a segment
(see Tables 5-1 and 5-2). With these maximum cable lengths, however, note that
no other nodes may be situated between the two RS 485 repeaters. You can
connect up to ten RS 485 repeaters in series.
Note that you must count an RS 485 repeater as a node of the MPI network in the
total number of all nodes to be connected, even if it is not assigned its own
MPI number. The use of RS 485 repeaters reduces the number of nodes.