Siemens SIMATIC NET PROFIBUS Owner's Manual page 382

Infrared Link Modul (ILM)
9 Displays
POWER
green LED not lit
lit green
TX
yellow/orange LED not lit
lit yellow
lit orange
RX
yellow LED not lit
lit yellow
LOW
red LED not lit
lit red
ERROR
red LED not lit
lit red
Copyright by Siemens
No power supply or internal power supply defective or ribbon ca-
ble not plugged in.
Power supply OK
Data not sent optically
Data are sent, acknowledgment bit correctly received or acknow-
ledgment bit mechanism not activated.
Data being sent, acknowledgment bit activated but not correctly
received.
Data not optically received
Data optically received
Receive level OK (RX LED lit)
no receive level (RX LED also not lit)
Data optically received, the level is however low (RX LED also lit)
risk of data errors
Infrared level at receiver is not critical
Infrared level at receiver is critical, risk of data errors
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