Siemens CPU 1518-4 PN/DP ODK Manual page 35

Meaning of LINK RX/TX LED
Each port has a LINK RX/TX LED. The table below shows the various "LED scenarios" of
ports for the CPU 1518-4 PN/DP ODK.
Table 4- 2
LINK TX/RX LED
LED flashes green
LED flickers yellow
CPU 1518-4 PN/DP ODK (6ES7518-4AP00-3AB0)
Manual, 09/2016, A5E35681108-AA
Meaning of the LEDs
There is no Ethernet connection between the PROFINET interface of the
PROFINET device and the communication partner.
LED off
No data is currently being sent/received via the PROFINET interface.
There is no LINK connection.
The "LED flashing test" is being performed.
There is an Ethernet connection between the PROFINET interface of your
PROFINET device and a communication partner.
LED lit green
Data is currently being received from or sent to a communications partner
on Ethernet via the PROFINET interface of the PROFINET device.
Interrupts, error messages, diagnostics and system alarms
4.1 Status and error display of the CPU
Meaning
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