Siemens Simatic S7-300 CPU 31xC Series Installation And Operating Instructions Manual page 63

RS 485 repeater
Type
RS 485 repeater
Purpose
RS485 repeaters are used to amplify data signals on bus lines and to couple bus segments.
You require this RS 485 Repeater in the following situations:
• more than 32 network nodes
• when interconnecting a grounded with an ungrounded segment
• when exceeding the maximum line length in a segment
Longer cable lengths
If you want to implement cable lengths above those permitted in a segment, you must use
RS485 repeaters. The maximum cable length possible between two RS 485 repeaters
corresponds to the cable length of a segment. Please note that these maximum cable
lengths only apply if there is no further node interconnected between the two RS 485
repeaters. You can connect up to nine RS 485 repeaters in series. Please note that you
have to add the RS 485 repeater when you determine the number of nodes in your subnet,
even if it is not assigned its own MPI/PROFIBUS address.
Reference
• Technical data about the RS 485 repeater can be found in the product information.
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
Configuring
4.11 Planning subnets
Order number
6ES7 972-0AA00-0XA0
4-39