Siemens SIMATIC S7-1500R/H Manual page 35

Interrupts, diagnostics, error messages and system events
4.1 Status and error display of the CPU
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, 11/2019, A5E42011886-AB