Siemens SIMATIC S7-1500R/H

LINK TX/RX LED Meaning
Flashes green
The CPU performs an LED flash test.
Illuminated green
There is a connection between the interface of the device and a communication partner.
The redundancy connections are OK.
LED flashes
yellow/green
Data is currently being received or sent by a communication partner via the interface of the
device.
NOTE
"LED" instruction
You can read the status (e.g. "On" or "Off") of LEDs of a CPU or a module using the "LED"
instruction. Note, however, that it is not possible to read the LED status of the LINK RX/TX
LEDs on all S7-1500 R/H CPUs.
You can find additional information on the "LED" instruction in the STEP7 online help.
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CPU1517H-3PN (6ES7517-3HP00-0AB0)
Equipment Manual, 11/2022, A5E42011886-AD
Interrupts, diagnostics, error messages and system events
5.1 Status and error display of the CPU