Siemens SIMATIC S7 System Manual page 579

Symptom
Serial communications (RS-485 or RS-
232) are damaged when connecting to
an external device.
Either the port on the external device or
the port on the CPU is damaged.
Other communications problems
(STEP 7-Micro/WIN SMART)
Error handling
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
Possible cause
The communications cable can provide
a path for unwanted currents if all non-
isolated devices, such as PLCs, com-
puters, or other devices do not share
the same network circuit common ref-
erence. The unwanted currents can
cause communications errors or dam-
age to electric circuits.
Debugging and troubleshooting
10.7 Hardware troubleshooting guide
Possible solution
Refer to the wiring guidelines in
•
Chapter 3 and to the network guide-
lines in Chapter 8.
Purchase network isolators or iso-
•
lated RS485-to-RS485 repeaters
when you connect devices that do
not have a common electrical refer-
ence.
Refer to Appendix F for information
about article numbers for S7-
200 SMART equipment.
Refer to Chapter 8 for information
about network communications.
Refer to Appendix C for information
about error codes.
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