Siemens SIMATIC NET PROFIBUS manual What the LED indicators and signaling contacts mean

5 LED Indicators and Troubleshooting 5.1 LED Indicators

LED Indicator		Possible causes
CH1	 lights yellow	Signals are being received on the RS 485 bus line
electric	 not lit	– Bus subscriber is not connected
		– Connected bus subscriber is not switched on
		– One or both conductors in the RS 485 bus line is broken
	 flashes/lights red	Sporadic interference signals because
		– the RS 485 bus line being insufficiently shielded
		– an open RS 485 bus line, i.e. it is only connected to the module at one end
		– the RS 485 segment is not terminated or only terminated at one end
		– an RS 485 bus terminal or terminal connector has been plugged in/ pulled out
		Permanent interference because
		– conductors A and B in the RS 485 bus line have been transposed
		– of an RS 485 bus line short circuit
		– the send time has been exceeded caused by a bus subscriber in a bus
		segment connected to Port 1
		– module and another bus subscriber connected via Port 1 are both sending at
		the same time (e.g. because an address has been assigned twice, the setting
		of the slot time is too low, or during lifting of the segmentation in the optical
		line, see Chap. 3.1.1)
		– RS 485 driver of the module is defective (e.g. after lightning strike)
CH2, CH3	 lights yellow	PROFIBUS frames are being received at the optical port
optical		Operating mode ”Line with optical fiber link monitoring“ and
		”Redundant optical ring“
	 not lit	Transmission rate has not yet been recognized – LED ”System“ flashes red
		– No transmitting bus subscriber present
		– Send and receive optical fibers have been transposed
		– No partner module connected or partner module is not switched on
		– Connected partner module is defective
		Transmission rate has been recognized - LED ”System“ flashes green
		– If the operating mode ”Redundant optical ring“ has been set, the optical port
		works as a stand-by port. There is no malfunction in the OLM or the optical
		fiber.
		– If one of the operating modes ”Line with optical fiber link monitoring …“ has
		been set, no PROFIBUS frames are received at the optical port. There is no
		malfunction in the OLM or the optical fiber.
		Transmission rate has been recognized – LED ”System“ lights green or
	 flashes yellow	flashes red/green
		– No transmitting bus subscriber present (optical fiber connection is OK)
	 lights red	– Send and receive optical fibers have been transposed
		– No partner module connected or partner module is not switched on
		– Connected partner module is defective
		– Send time of connected partner module has been exceeded
		– An optical fiber line is broken
		– Optical fiber link to partner module is too long
		– Loose connection in an optical fiber connector
		– Optical fiber in the optical fiber connector is loose
		– When using a redundant optical ring: if a fault in the optical fiber has been
		corrected but the port LEDs on both of the OLMs concerned still light red,
		check whether parameter HSA has been set as described the in Chap. 3.3.
	 flashes red/yellow	– Fault occurs periodically (see above)
		– Loose connection in an optical fiber connector
		– Optical fiber in the optical fiber connector is loose
		– Only one active bus subscriber is connected, which only sends tokens to
		itself. A fault should not be signaled as soon as a second subscriber is
		activated.
		Operating mode ”Line without optical fiber link monitoring“
	 lights yellow	Signals are received at the optical port.
	 not lit	– No transmitting bus subscriber present
		– Send and receive optical fibers have been transposed
		– No partner module connected or partner module is not switched on
		– Connected partner module is defective

Table 2: What the LED indicators and signaling contacts mean

Signaling contact

no signal no signal

signal

no signal

no signal

no signal

no signal signal

signal

no signal no signal

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