Problem Definition: Bridging PROFIBUS DP to Ethernet Across 600 m
A field installation uses an ET 200S IM151-8 PN/DP (order number 6ES7151-8AB01-0AB0 or successor 6ES7151-8AB02-0AB0) as the head-end for a small remote I/O cluster. The interface module exposes a downstream PROFIBUS DP master port to talk to distributed slaves, and an upstream PROFINET/Ethernet port back to the controller. The operator PC, located in the Central Control Room (CCR) approximately 600 m away, has no PROFIBUS interface, only Ethernet. The existing copper PROFIBUS segment is running at 187.5 kbit/s and is being used as a long-haul data highway back to the CCR.
The objective is to terminate PROFIBUS DP near the field, convert the cyclic data to standard Ethernet frames (PROFINET or S7 communication), and then transport those Ethernet frames the remaining distance to the operator PC. Because 100BASE-TX twisted pair is limited to 100 m per segment (IEEE 802.3u Clause 25) and the existing copper PROFIBUS cable cannot be re-pulled, the conversion point must be paired with a fiber-optic media conversion in series with the gateway.
Physical-Layer Constraints: Copper vs Fiber, Bit Rate vs Distance
Before selecting a gateway, the distance budget must be validated against the protocol limits. The PROFIBUS segment lengths specified by IEC 61158-2/EN 50170 and the PROFIBUS & PROFINET International (PI) installation guidelines are:
| Baud rate | Max segment length, copper (Type A, 3-wire, shielded) | Max segment length, plastic fiber (POF/PCF) | Max segment length, glass fiber (62.5/125 µm, 9/125 µm) |
|---|---|---|---|
| 9.6 kbit/s | 1 200 m | — | — |
| 19.2 kbit/s | 1 200 m | — | — |
| 45.45 kbit/s | 1 200 m | — | — |
| 93.75 kbit/s | 1 200 m | — | — |
| 187.5 kbit/s | 1 000 m | 50 m (POF) / 300 m (PCF) | ≤ 15 km with OLM |
| 500 kbit/s | 400 m | 50 m (POF) / 300 m (PCF) | ≤ 15 km with OLM |
| 1.5 Mbit/s | 200 m | 50 m (POF) / 200 m (PCF) | ≤ 15 km with OLM |
| 3 / 6 / 12 Mbit/s | 100 m | 50 m (POF) / 100 m (PCF) | ≤ 15 km with OLM |
For the application at hand, the PROFIBUS leg from the IM151-8 PN/DP to the gateway will operate at 187.5 kbit/s, which permits 1 000 m of copper in a single segment. The bottleneck is the 600 m Ethernet leg from the gateway to the PC. Standard Cat5e/Cat6 reaches only 100 m, so the Ethernet segment must be broken by a fiber pair and a media converter or managed switch.
Three Architectures for the Conversion
Three solutions solve the problem. The first is the canonical one (gateway + fiber switch), the second replaces the copper PROFIBUS with fiber PROFIBUS and keeps the gateway at the field end, and the third uses a managed industrial Ethernet switch pair to carry the PROFINET side of the IM151-8 directly to the PC.
Architecture A: IE/PB Link PN IO + SCALANCE X Fiber Switch
The PROFIBUS DP master port on the IM151-8 is connected to a Siemens IE/PB Link PN IO (6GK1411-5BB00). The IE/PB Link translates DP frames to PROFINET IO on its Ethernet side. The Ethernet side of the link is then uplinked to a SCALANCE X204-2 (6GK5204-2BB00-2AF2) in the field. A multi-mode glass fiber pair (62.5/125 µm or 50/125 µm, 1300 nm) runs 600 m to a second SCALANCE X204-2 in the CCR. The PC terminates on the CCR switch with a standard RJ45 patch cable.
Architecture B: PROFIBUS OLM G12 Fiber Link + IE/PB Link
The 600 m PROFIBUS copper segment is replaced with a fiber pair using two OLM G12 modules (6GK1502-3CB10). PROFIBUS DP at 187.5 kbit/s now rides on 62.5/125 µm glass fiber. The IE/PB Link is installed in the CCR, converts DP to PROFINET locally, and the operator PC connects via a 2 m patch cable. This is the cleanest topology because it removes the fiber/Ethernet media question entirely from the field.
Architecture C: SCALANCE X Pair with PROFINET Socks
No gateway is used at all. The IM151-8 PN/DP is configured as a PROFINET IO device and talks directly to a PROFINET IO controller. The 600 m fiber is terminated by two SCALANCE XB-008 or XC-208 switches (6GK5208-0BA00-2AF2) in a ring or point-to-point topology. The PC runs a PROFINET supervisor or WinCC Runtime. This option requires the upstream controller to host the IM151-8 as an IO device; if the existing controller is PROFIBUS-only, the IE/PB Link must be re-inserted.
Selecting the Correct IE/PB Link Variant
Two IE/PB Link PN IO variants are still in service and supported by Siemens:
| Article number | MLFB | PROFINET ports | PROFIBUS master | Web server | Firmware baseline (FW V3.x) |
|---|---|---|---|---|---|
| 6GK1411-5AB00 | IE/PB Link PN IO | 1 × RJ45 | DP-V0/V1 master | Yes (limited) | FW V3.0.0 and above |
| 6GK1411-5BB00 | IE/PB Link PN IO (current) | 1 × RJ45 (10/100 Mbit/s) | DP-V0/V1/V2 master | Yes (full) | FW V4.0.x and above |
Order the 6GK1411-5BB00 for new installations. It supports DP-V2 clock-synchronization passthrough, has a more recent web diagnostics page (HTTP on port 80, secure via HTTPS with cert upload on FW 4.1+), and accepts firmware updates via the integrated TFTP server at address 192.168.0.10/24. The 6GK1411-5AB00 is end-of-life for spare parts since 2018 but is still firmware-maintained.
SCALANCE X204-2 Fiber Switch Configuration
The SCALANCE X204-2 is a managed Layer 2 switch with four 10/100BASE-TX ports and two 100BASE-FX ports (SC sockets for multi-mode glass fiber). Key configuration data:
- Default IP: 192.168.0.10 / 24, default password:
admin(change on first login) - Web server: ports 80 and 443; Telnet/SSH: 23 / 22
- PROFINET IO device (can be configured as a PN device for diagnostics)
- Fiber range: 0 to 5 000 m on 50/125 µm, 0 to 4 000 m on 62.5/125 µm, 1300 nm, SC duplex
- Power: 24 VDC ±20 %, redundant feed terminals, max 4.5 W consumption
Configure the two SCALANCE X204-2 switches as a transparent point-to-point link. Enable LLDP on all ports, set the PROFINET priority (VLAN tag 0, priority 6) for the port facing the IE/PB Link, and disable Energy Efficient Ethernet (EEE) on the SC sockets — EEE is known to introduce 2-3 ms latency spikes that break PROFINET IRT timing.
TIA Portal Hardware Configuration for the IE/PB Link PN IO
The IE/PB Link PN IO must be inserted into the PROFINET topology as an IO device. The procedure is identical in STEP 7 V5.7 and TIA Portal V16+.
- Open the device configuration of the PROFINET IO controller (the S7-1500 or S7-300 CPU).
- From the hardware catalog, drag Other field devices > PROFINET IO > Gateway > IE/PB Link PN IO > 6GK1411-5BB00 into the PROFINET subnet. Assign a unique device name (for example,
ie-pb-link-01) and an IP address (192.168.0.50 / 24). - Assign the IE/PB Link as a PROFINET IO device under the controller. Set the update time to 1 ms for acyclic slots and 4 ms for cyclic slots if any slaves require it; 1 ms is fine for slow I/O.
- Open the slot configuration of the IE/PB Link. Insert a DP master slot and add the PROFIBUS slaves to the lower-level DP master system. Each DP slave is mapped as a slot on the IE/PB Link, with I/O addresses that the controller can read via PROFINET.
- Compile and download the configuration. Use the PROFINET commissioning wizard in TIA Portal to assign the device name via the MAC address sticker on the link.
Commissioning the 600 m Fiber Link
- Verify the cable plant: glass fiber, 62.5/125 µm OM1 or 50/125 µm OM3, SC duplex connectors. Measure attenuation with an optical light source + power meter (1310 nm). Budget ≤ 6 dB total loss for a 600 m run, including 1 dB per connector pair and 0.4 dB per splice.
- Terminate the fiber at the field SCALANCE X204-2 Port 5 (or 6) and the CCR SCALANCE X204-2 Port 5. Lock the SC connectors with the bayonet; an unseated connector will produce a -40 dBm receive level and the link will flap.
- Power both SCALANCE X204-2 units from separate 24 VDC supplies (A/B feed redundancy).
- Connect the IE/PB Link RJ45 to Port 1 of the field SCALANCE X204-2 using a Cat5e patch ≤ 3 m.
- Connect the operator PC to Port 1 of the CCR SCALANCE X204-2 with a Cat5e patch.
- Power the IE/PB Link. The
SF,BF, andLINKLEDs on the IE/PB Link should settle to green on the PROFINET side within 30 s. - Open the IE/PB Link web page (http://192.168.0.50) and check Diagnostics > PROFINET > AR Status. The Application Relationship should report
AR established, no errors. - Open Diagnostics > PROFIBUS. All configured DP slaves should show
Slave OK, data exchange. Address 0 (master) reserves the master's own bus parameters; slave address 1, 2, 3, ... follow.
Verification Tests
Run the following acceptance tests before handing the link over to operations.
| Test | Method | Pass criterion |
|---|---|---|
| PROFINET AR establishment | Web page on IE/PB Link, port 80 | AR state = Established, no alarms, slot 0 diagnostic = 0x0000 |
| DP slave live list | Web page or STEP 7 online > Accessible Nodes | All configured slaves return 0F in their status byte and the bus scan reports 100 % participation |
| Cyclic I/O round trip | Force an output bit on a DP slave, read it back from the HMI | Update time ≤ 4 ms, jitter ≤ 0.5 ms, no dropped telegrams over 10 min |
| Fiber loss | 1310 nm OTDR trace or power meter | Total loss ≤ 6 dB end-to-end |
| PROFINET alarms | TIA Portal online > Diagnostics > Alarms | Zero Station failure or Port link down events in 24 h soak |
| Web diagnostics on PC | Open the IE/PB Link web page from the PC browser | Page loads in ≤ 1 s, no SSL warning if HTTPS enabled |
| Watchdog on DP side | Pull the PROFIBUS connector, observe IE/PB Link BF LED |
BF LED goes red within 1 s, station failure alarm is raised on the controller |
Troubleshooting Matrix
| Symptom | Likely cause | Diagnostic step | Corrective action |
|---|---|---|---|
IE/PB Link BF (bus fault) LED red, SF red |
PROFIBUS wiring break, slave address conflict, or termination missing | Disconnect PROFIBUS at the IE/PB Link, measure A-B line resistance; expected 220 Ω bus termination at each end | Enable terminating resistor on the IE/PB Link (slide switch on bottom); verify one and only one terminator at each end of the segment |
LINK LED off on field SCALANCE Port 5 |
Fiber crossed (TX/RX), dirty connector, or fiber break | Swap fiber pairs at one end; clean connectors with IEC 61300-3-35 cleaning tool; run OTDR | Replace patch cord; re-strap cable; re-terminate if loss > 6 dB |
| PROFINET AR repeatedly drops and re-establishes every 30 s | Watchdog time on the controller too short, or EEE enabled on SC port | Read IE/PB Link web page > PROFINET > AR Statistics | Disable Energy Efficient Ethernet on SCALANCE Port 5/6; raise the PROFINET watchdog to 3 × the configured update time |
DP slaves visible in bus scan but data exchange fails for one slave |
Slave address duplicate, or different baud rate negotiation on that slave | Compare the slave's DIL-switch address with the TIA Portal configuration | Re-address the slave to a free address; ensure all slaves support auto-baud to 187.5 kbit/s |
| Operator PC cannot reach IE/PB Link web page | VLAN mismatch on the SCALANCE or wrong subnet on the PC NIC | Set the PC to DHCP; check ARP table on the PC | Place the PC and the IE/PB Link in the same VLAN (untagged); set the PC NIC to 192.168.0.x / 24 with gateway 192.168.0.1
|
| Long commissioning time (> 60 s) before data exchange | Default PROFINET device name is still in use; controller waits for the name assignment protocol | Run TIA Portal > Online > Accessible Nodes > Assign PROFINET device name | Assign ie-pb-link-01 as the device name to the IE/PB Link MAC |
| Intermittent DP faults when the field cabinet door is closed | EMC coupling into PROFIBUS cable from VFD or contactor | Scan with a spectrum analyzer on the PROFIBUS cable shield | Re-route the PROFIBUS cable ≥ 200 mm from VFD output cables; ground the shield at both ends with 360° EMC glands |
Spare-Parts and Documentation References
- IM 151-8 PN/DP interface module — Siemens Industry Online Support entry for 6ES7151-8AB01-0AB0 (function manual, FW V4.x and V5.x release notes).
- IE/PB Link PN IO (6GK1411-5BB00) — device manual and firmware V4.1.1 release notes; the manual covers PROFINET IO device mode, DP-V1 master, S7 routing, and web server pages.
- SCALANCE X-200 product family — configuration manual for X-200 managed switches, including PROFINET QoS, LLDP, and PROFINET IO device integration.
- OLM G11 / G12 (6GK1502-2CB10 / 6GK1502-3CB10) — operating instructions for the PROFIBUS Optical Link Module, with link-budget calculations and redundant ring topology.
- PROFIBUS Installation Guideline 8.2 — PI (PROFIBUS & PROFINET International) wiring guidelines, the binding document for cable types, segment lengths, and shielding practice.
Field-Proven Caveats
Baud-rate matching. When the IE/PB Link is configured as a DP master, the link auto-negotiates to the highest baud rate supported by every slave. With 187.5 kbit/s slaves, the link negotiates down to 187.5 kbit/s, and the segment length is then 1 000 m. If a 1.5 Mbit/s slave is later added, the link auto-upgrades and the segment length collapses to 200 m. Document the worst-case slave at design time and pin the baud rate explicitly in the IE/PB Link if you cannot guarantee the slave roster.
Watchdog vs update time. The PROFINET watchdog on the IO device slot of the IE/PB Link is computed by the controller. Setting a 1 ms update time forces a 3 ms watchdog by default; long fiber paths or noisy EMC environments can cause single missed frames. The conservative rule for a 600 m industrial fiber path is update time ≥ 4 ms with a watchdog of 12 ms (3 × update).
PROFINET conformance class. The IE/PB Link PN IO implements Conformance Class B (CC-B). The SCALANCE X204-2 is also CC-B. Do not connect the field segment to a CC-A only device; PROFINET LLDP and SNMPv2c will fail to negotiate and the link will fall back to legacy mode with degraded diagnostics.
Cybersecurity. Disable the FTP and TFTP servers on the IE/PB Link once commissioning is complete. Change the default admin password. Restrict port 80 to a maintenance VLAN or close it; port 443 with a customer-supplied certificate is the supported secure path on FW V4.1 and above.
Spare strategy. Stock one spare IE/PB Link (6GK1411-5BB00) preloaded with the project configuration. The device's configuration is stored on a pluggable C-PLUG (6GK1900-0AB00). A swap is performed by moving the C-PLUG; the new link boots with the saved configuration in under 60 s.
Can the PROFIBUS cable be left in place and used for Ethernet at 600 m?
No. PROFIBUS DP cable is a shielded 3-wire RS-485 medium and does not support 10/100BASE-TX signaling. You would have to pull new Cat5e/6 twisted pair, and that cable is limited to 100 m. The correct reuse path is to keep the PROFIBUS cable as-is and add fiber for the Ethernet portion of the link, or replace the PROFIBUS copper with PROFIBUS fiber using OLM G12 modules.
Do I need the IE/PB Link if the upstream controller already speaks PROFINET?
Not necessarily. If the S7 controller is PROFINET-native, the IM151-8 PN/DP can be connected directly to the controller as a PROFINET IO device, and the PROFIBUS slaves connect to the IM151-8's downstream DP master port. The IE/PB Link is only required when the controller is PROFIBUS-only or when the operator PC must reach the slaves via Ethernet and no PROFINET controller is available.
What is the difference between IE/PB Link PN IO and DP/DP Coupler?
The IE/PB Link (6GK1411-5BB00) converts PROFIBUS DP to PROFINET IO and acts as a PROFINET IO device. The DP/DP Coupler (6GK1500-3AB00) is a PROFIBUS-to-PROFIBUS bridge that connects two DP masters and exchanges a fixed amount of I/O between them. The DP/DP Coupler does not produce Ethernet frames and cannot be used to reach an Ethernet PC.
At 187.5 kbit/s, can the PROFIBUS segment be extended to 600 m without an OLM?
Yes. The PROFIBUS specification permits up to 1 000 m of copper at 187.5 kbit/s. The IE/PB Link can terminate a 600 m copper segment directly on its 9-pin D-sub PROFIBUS port. The fiber is only required on the Ethernet side, between the IE/PB Link and the operator PC's switch, because 100BASE-TX copper is limited to 100 m.
Which SCALANCE switch should be used for the 600 m fiber link?
SCALANCE X204-2 (6GK5204-2BB00-2AF2) is the standard choice: four 10/100BASE-TX copper ports plus two 100BASE-FX SC ports. For harsh environments, use SCALANCE X208-2 (six copper + two fiber) or the IP65 SCALANCE XR324-12M. The X-200 family supports PROFINET CC-B and is a PROFINET IO device in its own right, which is useful for centralized diagnostics from the controller.
Can the operator PC talk to the PROFIBUS slaves through the IE/PB Link without a PLC in the loop?
Yes, if the operator PC is configured as a PROFINET IO controller and the IE/PB Link is a PROFINET IO device. The PC runs a PROFINET supervisor stack (Siemens Primary Setup Tool, PROFINET Inspector, or a custom application using the PROFINET IO base API). The IE/PB Link then exposes each DP slave as a slot with I/O data. Alternatively, the PC can use the IE/PB Link web server for read-only diagnostics without joining the PROFINET AR.
What is the maximum number of DP slaves behind one IE/PB Link PN IO?
The link supports up to 32 DP-V0 slaves per DP master segment, with a maximum of 244 input bytes and 244 output bytes total per segment. For DP-V1 or DP-V2 slaves with acyclic parameter access, the figure is reduced to 32 slaves / 244 bytes / 32 acyclic records. Practical installations stay well below these limits because of the per-slot PROFINET payload cap of 1 440 bytes per slot and 1 024 bytes per subslot.