SCALANCE XB004-1LD PROFINET Communication with S7-1200 Controllers
The SCALANCE XB004-1LD is an unmanaged Industrial Ethernet switch from the Siemens SIMATIC NET SCALANCE XB-000 family, frequently deployed as a low-cost segment coupler in PROFINET cells where a single PROFINET IO controller (for example, an S7-1200) must exchange process data with one or more PROFINET IO devices (additional S7-1200 CPUs) over a longer-reach glass fiber link. This reference consolidates the configuration requirements, conformance class boundary, fiber specifications, and the practical limits of using an unmanaged switch in a PROFINET cell.
1. Problem Statement and Target Topology
The target topology is a linear PROFINET cell where:
- PROFINET IO controller = SIMATIC S7-1200 (e.g., CPU 1214C DC/DC/DC, firmware V4.x or later) on Port 1 of switch A.
- PROFINET IO device = SIMATIC S77-1200 (e.g., CPU 1215C DC/DC/DC) on Port 1 of switch B.
- Switch A = SCALANCE XB004-1LD, Switch B = SCALANCE XB004-1LD.
- Uplink between the two switches = SC port, single-mode or multi-mode glass fiber (10/125 µm) patch cord.
Because the XB004-1LD is an unmanaged device, the question that always arises is: Will PROFINET RT run across two of these switches with a glass fiber uplink, and what features are lost? The short answer: PROFINET RT Class 1 traffic will run, but LLDP-based topology and the diagnostic functions that depend on it will not.
2. SCALANCE XB004-1LD Hardware Reference
The SCALANCE XB004-1LD is the variant of the XB-000 line that provides an integrated SC fiber socket for 10/125 µm single-mode glass fiber (in practice, multimode 50/125 or 62.5/125 fibers with the appropriate SC patch cords are accepted on the optical port, since the optical budget tolerates both). The full datasheet is in the SIMATIC NET SCALANCE XB-000 Operating Instructions (PDF).
| Parameter | SCALANCE XB004-1LD |
|---|---|
| Article number (MLFB) | 6GK5004-1BD00-1AB2 (typical European catalog number) |
| RJ-45 ports (electrical) | 4 x 10/100 Mbps, MDI/MDIX auto-crossover |
| Optical port | 1 x SC duplex, 100BASE-FX, 10/125 µm glass fiber |
| Link distance (optical) | Up to 26 km on 9/125 single-mode (model-specific); 3 km typical for the 1LD variant on single-mode 10/125 |
| Power supply | 24 V DC (18 to 32 V) and now 24 V AC per the Siemens Support entry 109481776 |
| Power consumption | Approximately 3.6 W at 24 V DC |
| Operating temperature | −10 °C to +60 °C |
| Protection class | IP30 housing, DIN rail mount |
| Management | Unmanaged – no Web UI, no CLI, no PROFINET device model |
| Switching method | Store-and-forward, 1 K MAC address table (sufficient for an S7-1200 cell) |
3. PROFINET Conformance Class Boundary
PROFINET switches are graded into Conformance Classes (CC-A, CC-B, CC-C) per the PI (PROFIBUS Nutzerorganisation) PROFINET Installation Guide. The class determines which PROFINET services are guaranteed to function through the switch.
| Conformance Class | Required Switch Functions | XB004-1LD Status |
|---|---|---|
| CC-A | 100 Mbps, full-duplex, store-and-forward, auto-crossing, auto-negotiation, auto-polarity, VLAN priority (IEEE 802.1Q), no blocking of PROFINET frames | YES – XB004-1LD meets CC-A |
| CC-B | CC-A + LLDP forwarding, prioritized handling of PROFINET RT/IRT frames, port statistics, SNMP/diagnostics | NO – XB004-1LD does not forward LLDP per port topology; the switch is transparent to LLDP frames in practice, but does not originate them |
| CC-C | CC-B + cut-through switching for IRT, jitter < 1 µs, bandwidth reservation | NO – IRT not supported |
For the target application – PROFINET RT (not IRT) – CC-A is sufficient. PROFINET RT Class 1 (the default update class for S7-1200 PROFINET IO) is a soft real-time class with a typical update time of 1 ms to 512 ms; it tolerates store-and-forward latency and is unaffected by the absence of LLDP forwarding.
4. Required Layer-2 Features Checklist
Confirm each of the following in the XB004-1LD data sheet before commissioning. All of these are listed in the SCALANCE XB-000 Operating Instructions:
- Auto-crossover (MDI/MDIX) – required; XB004-1LD: YES.
- Auto-negotiation – required; XB004-1LD: YES (electrical ports only; SC port fixed at 100 Mbps FD).
- Auto-polarity – required; XB004-1LD: YES.
- Priority (IEEE 802.1Q VLAN tag handling) – required; XB004-1LD: transparent to VLAN tags, will not strip the PCP byte.
- Fast Ethernet 100BASE-TX / 100BASE-FX (IEEE 802.3u) – required; XB004-1LD: 100BASE-TX on RJ-45, 100BASE-FX on SC.
- Full-duplex – required; XB004-1LD: YES, both fixed.
- IEEE 802.1Q (tagged frame forwarding) – required; XB004-1LD: transparent pass-through.
- LLDP forwarding – only needed for CC-B services; XB004-1LD: not required for RT communication.
The XB004-1LD complies with the first seven items, which is the complete set of requirements for PROFINET RT Class 1 with CC-A switches.
5. Why LLDP Is Not Required for PROFINET RT
LLDP (IEEE 802.1AB) is a Layer-2 neighbor-discovery protocol. In a PROFINET cell, it is used by the IO controller and IO supervisory tools to:
- Build the topology view in TIA Portal / PRONETA.
- Detect the actual physical path between controller and device for neighborhood-failure detection (one of the diagnostic features required for CC-B).
- Enable the device replacement without programming device feature, which substitutes a spare device whose name and IP are read by the supervisor from the LLDP-advertised neighbor of the previous device.
None of these are part of the data-plane PROFINET RT exchange. The PROFINET RT frame is a standard Ethernet frame on UDP port 49152 (or configurable) with no LLDP payload. As long as the switch forwards standard Ethernet frames (which XB004-1LD does), PROFINET RT runs. The cost is that:
- Topology in TIA Portal must be drawn manually.
- Device replacement without PG is not supported.
- Port-level diagnostics from the IO controller to the switch are not possible (the switch is not a PROFINET device anyway).
6. Fiber Optic Link Specification (10/125 µm)
The SC port of the XB004-1LD is specified for glass fiber 10/125 µm (single-mode, OS1/OS2). When using 50/125 µm or 62.5/125 µm multimode fiber with the same SC connector, the optical power budget must be checked against the SCALANCE XB-000 data sheet. Patch cords must be SC duplex on both ends and crossed (TX to RX, RX to TX) – this is the standard fiber patch configuration.
| Fiber type | Typical max distance on 100BASE-FX | Notes |
|---|---|---|
| 10/125 µm (SM, OS1) | up to 26 km | Standard rating, lowest attenuation |
| 50/125 µm (MM, OM2/OM3) | up to 2 km (OM2) / 1 km (OM3 for some Siemens FXR variants) | Verify port spec |
| 62.5/125 µm (MM, OM1) | up to 1 km | Verify port spec |
Attenuation budget for 100BASE-FX at 1310 nm is typically 8 dB on single-mode. Always clean the SC ferrule with a fiber optic cleaner before insertion; a contaminated connector is the single most common cause of intermittent PROFINET faults on a fiber uplink.
7. TIA Portal Configuration (V15.1 to V18+)
Because the XB004-1LD is unmanaged and is not registered as a PROFINET device, configuration is on the S7-1200 side only.
7.1 Controller (S7-1200 IO Controller)
- Open the S7-1200 device view in TIA Portal.
- Select the PROFINET interface of the CPU.
- Assign an IP address, e.g., 192.168.0.1, subnet mask 255.255.255.0.
- Enable Use this interface as PROFINET IO controller.
- In PROFINET interface > Port 1 disable the port assignment of the switch (no partner port) – the switch is not a PROFINET device, so the topology editor will show Other or no node.
7.2 Device (S7-1200 as IO Device)
- Open the S7-1200 IO device device view.
- Assign a unique IP address, e.g., 192.168.0.2, subnet mask 255.255.255.0.
- Assign a PROFINET device name, e.g.,
io-device-1. - In the IO controller project tree, add the IO device to the controller.
- Configure the update time. For an RT Class 1 cycle, use the default factor; for the 2-second application referenced in the source, set the update time to 2 ms × 1000 = 2 s, or select Send clock = 1 ms and Reduction ratio = 2000.
7.3 Cabling and Link Check
- Connect controller to XB004-1LD switch A, Port 1 (RJ-45) of switch A.
- Connect IO device to XB004-1LD switch B, Port 1 (RJ-45) of switch B.
- Connect SC port of switch A to SC port of switch B with a 10/125 µm duplex SC patch cord (crossed: TX-A → RX-B, RX-A → TX-B).
- Apply 24 V DC or 24 V AC to the redundant power terminals of both XB004-1LD units (per the 24 V AC support update).
- Check the green port LEDs – link LED on each RJ-45 and on the SC port confirms physical link.
8. Update-Time Calculation for the Source Application
The original application uses 10 bytes of I/O data per direction with a 2-second cycle. The minimum update time for PROFINET RT Class 1 is bounded by:
T_update = T_sendclock × Reduction_ratio
With the S7-1200 default send clock of 1 ms, the reduction ratio for 2 seconds is 2000. The IO payload of 10 bytes (well under the default 256-byte I/O data record limit) requires no special configuration. The store-and-forward latency of the XB004-1LD is below 10 µs per hop – negligible compared to the 2 s update.
For a 1 ms update on the same 10 bytes (the realistic minimum for S7-1200 with PROFINET RT, not IRT), the XB004-1LD is still sufficient. The switch becomes a constraint only when IRT with cut-through (CC-C, jitter < 1 µs) is required – in which case a SCALANCE XC-200, XC-300, or XR-500 managed switch is mandatory.
9. Limitations and Trade-Offs
| Feature | XB004-1LD (CC-A) | SCALANCE XC208 (CC-B) |
|---|---|---|
| PROFINET RT (1 ms to 2 s) | Yes | Yes |
| PROFINET IRT (high-performance, < 1 ms isochronous) | No | No (CC-C required) |
| LLDP forwarding / topology | Transparent only | Yes, with diagnostics |
| Port statistics / SNMP | No | Yes |
| Device replacement without PG | No | Yes |
| Web management | No | Yes |
| Approximate cost (catalog) | ~ €300 | ~ €1000 |
For a 2-second, 10-byte exchange between two S7-1200 stations, the XB004-1LD meets the technical requirement. The decision driver is therefore the lifetime diagnostic and service value of the application, not the data-plane capability.
10. Troubleshooting Matrix
| Symptom | Likely cause | Check | Remedy |
|---|---|---|---|
| No link on SC port | TX/RX crossed incorrectly on patch cord, dirty ferrule, or wrong fiber type | Verify SC patch cord TX → RX; clean ferrule; check 10/125 µm spec | Replace patch cord; clean with one-click cleaner |
| Link up, PROFINET IO device not reachable | Wrong IP or duplicate PROFINET name in the cell | Ping 192.168.0.2 from the controller's programming port; check device name in the IO controller project | Assign unique IP and PROFINET name |
| Intermittent IO device faults (yellow SF LED on CPU) | Cable near VFD or unshielded section; aging SC connector; S7-1200 PROFINET name not yet assigned at startup | Replace fiber, check shielding, check device name assignment | Use shielded Cat 5e/6 on RJ-45 legs; pre-assign PROFINET name |
| TIA Portal shows "Partner port unknown" on controller | XB004-1LD is unmanaged – expected | Confirm this is informational, not an error | Either accept the warning or migrate to a managed switch if topology is required |
| PROFINET frame loss on long fiber | Optical budget exceeded (km, splices, dirty connectors) | Measure optical power with a 1310 nm FO power meter | Re-spec fiber type, replace splices, clean connectors |
| IO device shows "Device replaced" but no IO data | PROFINET device replacement feature used, requires CC-B switch | Verify switch class in PROFINET diagnostics | Use a CC-B switch (e.g., SCALANCE XC208) or assign name via PG manually |
11. Verification Procedure
- After configuration, compile and download to the IO controller.
- In the TIA Portal Online & Diagnostics view of the controller, open the PROFINET diagnostics – both the controller and the IO device should show Operational.
- Force a tag in the IO controller's watch table; observe the corresponding tag in the IO device's watch table (and vice-versa).
- Run PRONETA or Topology Editor and confirm the IO device is reachable – the XB004-1LD will not appear as a node, but the IO device should be visible as an end station.
- Log off, power-cycle both switches, and verify the IO device re-establishes without manual intervention (validates store-and-forward behaviour and PROFINET name persistence on the IO device).
12. Field-Proven Caveats
- Do not mix the SCALANCE XB-1LD (fiber) and XB004-1 (electrical) variants in the same cell without verifying the copper cable length – a cell that mixes a fiber uplink and long copper runs can exceed the 100 m copper limit if the remote switch sits more than 100 m from the field device.
- The XB004-1LD does not buffer frames during a broadcast storm; in a flat PROFINET cell with many IO devices, a single faulty device flooding ARP requests can affect the entire cell. Use managed switches in larger cells.
- Power supply: the support entry 109481776 confirms 24 V AC support, but verify the AC ripple under the load of the 24 V AC source – a heavily loaded AC transformer can introduce frame errors on the PROFINET cell.
- The XB004-1LD has no MAC address filtering or port security. For a cell that connects to a higher-level network, do not connect the XB004-1LD directly to the office VLAN; cascade through a managed boundary switch.
FAQ
Can PROFINET RT run between two S7-1200 stations across two SCALANCE XB004-1LD switches?
Yes. PROFINET RT Class 1 is a standard UDP/Ethernet data exchange on port 49152 and only requires a CC-A switch with 100 Mbps full-duplex, store-and-forward, auto-crossing, auto-negotiation, and IEEE 802.1Q transparency – all of which the XB004-1LD provides.
Does the SCALANCE XB004-1LD forward LLDP frames?
It forwards LLDP frames transparently as standard Ethernet multicast, but it does not originate LLDP, does not maintain a per-port LLDP neighbor table, and does not report port statistics. PROFINET CC-B services that depend on per-port LLDP (topology, device replacement without PG) therefore do not work through this switch.
What is the maximum update time I can use through the XB004-1LD?
There is no fixed upper bound from the switch. For S7-1200 PROFINET RT, the practical maximum update time is 512 ms with the default settings and up to several seconds when the reduction ratio is increased. The source application uses a 2-second update, which is well within the switch's capability.
Is the 10/125 µm SC port on the XB004-1LD single-mode or multimode?
The datasheet specifies 10/125 µm glass fiber (single-mode) with a typical reach of several kilometers at 1310 nm. 50/125 µm and 62.5/125 µm multimode patch cords can be used provided the optical power budget is respected and the SC connectors are SC duplex on both ends with TX/RX crossed.
Can I power the XB004-1LD from 24 V AC instead of 24 V DC?
Yes. Per the Siemens Support entry 109481776, the XB004-1, XB004-1LD, and XB005 variants support both 24 V DC and 24 V AC. Verify the AC source ripple and grounding to avoid PROFINET frame errors on the cell.