Configuring SINAMICS Link Between Two CU320-2 PN for Torque

1. Problem Definition: Drive-to-Drive Torque Coupling Without a Master Controller

Motion-control installations that use multiple SINAMICS S120 drive line-ups sometimes require drives connected to two physically separate Control Units to share load (motoring or regenerative) in real time. Typical examples are mechanically coupled gantry axes, winder/unwinder pairs, twin-motor test stands with a common shaft, and cross-CU master/follower arrangements in which a torque setpoint generated on one CU320-2 PN must be distributed to a drive that lives behind a second CU320-2 PN.

The question that immediately comes up in this scenario is: if there is no SIMATIC S7, no TIA PLC, no higher-level controller, and no PROFINET IO controller in the network, how does one CU320-2 PN locate the other on the wire and push a process word into it? The answer from the official SINAMICS S120 Communication Function Manual (SIOS entry ID 109740020, Section 11.6) is to use SINAMICS Link, or, if the firmware is at V4.7 or later and the two Control Units already share a Drive-CLiQ ring, to use OALINK (the "OA application link" cross-CU coupling over Drive-CLiQ).

2. The Two Production-Grade Solutions

Siemens documents two PLC-less methods for cross-CU drive-to-drive communication on SINAMICS S120. Both are designed to be commissioned entirely from the drive engineering tool, with no controller program and no GSDML import.

• SINAMICS Link — a fast, cyclic, peer-to-peer Ethernet protocol designed specifically for drive-to-drive data exchange without a controller. Configured in STARTER or Startdrive, it can carry 16-bit process words from any node to any other node on the same Ethernet segment. The relevant chapter is Section 11.6 of the SINAMICS S120 Communication Function Manual, available as a PDF at S120 Communication Function Manual 06/2019 (en-US).
• OALINK — a Drive-CLiQ-based direct coupling that is part of the OA (Open Architecture) application framework. Available from SINAMICS V4.7 for the CU320-2 PN, it allows two Control Units to exchange data over the same Drive-CLiQ ring that already connects Line Modules and Motor Modules, eliminating the need for an extra Ethernet cable. The OALINK documentation is published under SIOS entry 109477831 and SIOS entry 109475385.

Both options solve the "no master in the network" problem that the original question describes. The choice between them is a hardware-cabling and firmware-version decision, not a performance decision.

3. SINAMICS Link — Technical Fundamentals

SINAMICS Link is implemented in the firmware of every current SINAMICS S120 Control Unit (CU320-2 PN, CU320-2 DP, CU310-2 PN, CU310-2 DP) and uses the onboard Ethernet service interface. The transport is a Siemens-internal Layer-2 broadcast; it is not standard TCP/IP, and it is not PROFINET RT. The relevant engineering facts are summarised in the table below.

The 16-bit granularity is the most important detail for the torque-share problem. A torque setpoint in SINAMICS is a 32-bit N2 (normalized) value, scaled with the torque reference p2003 (in Nm). The high word and low word must be packed into two adjacent SINAMICS Link send slots on the source CU, then unpacked and re-assembled on the destination CU before being routed to the torque setpoint input of the receiving drive.

4. OALINK — Technical Fundamentals

OALINK is not a separate physical interface; it is an application that rides on top of Drive-CLiQ. The two CU320-2 PNs must already be connected in a common Drive-CLiQ topology, which is normally the case when a Line Module feeds Motor Modules on two different Control Units and the CUs are bridged via a DRIVE-CLiQ Hub (DMC20) or a direct coupling cable. The OA runtime exposes additional process-data connectors inside the DCC or OA environment on both CUs.

The advantage of OALINK is the absence of an extra cable run: it reuses Drive-CLiQ. The trade-off is that the receiving side must run a DCC chart (or an OA application block) to de-multiplex the data into the drive's setpoint channel, which is a higher-level programming exercise than the SINAMICS Link dialog.

5. Architecture Comparison

For a two-CU torque-share installation that already uses Drive-CLiQ to bridge the two CUs and runs on a recent firmware, OALINK is the lower-hardware option. For a greenfield installation with two independent cabinets, SINAMICS Link on a dedicated Ethernet segment is faster to commission and easier to document.

6. Hardware Wiring: Which Connector to Use

The CU320-2 PN has the following front-panel connectors relevant to drive-to-drive communication. Identify the correct connector before you start commissioning — wiring SINAMICS Link to the wrong port is the single most common commissioning error in this topology.

For SINAMICS Link between two CU320-2 PNs, wire X140 of CU #1 directly to X140 of CU #2 with a standard Cat5e or Cat6 patch cable. A small industrial Ethernet switch is acceptable on the cabinet, but it must be unmanaged, or managed with the SINAMICS Link ports in a dedicated VLAN with no PROFINET configuration applied.

7. Commissioning SINAMICS Link — Step-by-Step

The following procedure assumes STARTER V5.x with a current SINAMICS support package. Startdrive in TIA Portal is functionally identical; the dialog names match. Both Control Units must be on the same project and online-capable before starting.

7.1 Prerequisites

• Two CU320-2 PN with current firmware (V4.x or V5.x).
• STARTER or Startdrive installed, project open, both drives detected and online.
• Ethernet patch cable between X140 of the two CUs (no switch, or a dedicated Ethernet switch as described above).
• Static IP configuration on X140 of each CU (e.g. 169.254.1.1 and 169.254.1.2, mask 255.255.255.0).
• The two CUs are on the same project with the topology already commissioned (Line Modules, Motor Modules, drives green).

7.2 Procedure

1. Set the IP address on the service interface. In STARTER, navigate to the drive → Communication → Ethernet interface. Assign a fixed IP address and subnet to X140. Download to the drive. Repeat for the second CU on a different host number. Do not enable DHCP on this port.
2. Activate SINAMICS Link on CU #1. In the project tree, open Communication > SINAMICS Link. Tick Activate SINAMICS Link. Set the Node number to 1 for the source CU. Save and download.
3. Activate SINAMICS Link on CU #2. Repeat the activation on the partner CU with node number 2. Node numbers on a segment must be unique, and values 1–64 are permitted (0 = deactivated).
4. Configure the sender slots on CU #1. The dialog shows a 16-row table. For a 32-bit torque setpoint, reserve two adjacent slots, e.g. row 1 and row 2. In each row, select the BICO source: this is the output on the source drive that carries the torque setpoint (typically r79 "torque setpoint after filter" or r80 "torque setpoint at output of speed controller").
5. Configure the receiver slots on CU #2. On CU #2, open the SINAMICS Link dialog. Tick This drive is a receiver. In the receiver table, point row 1 to source node 1, send slot 1, and route the received 16-bit value to a BICO input on the receiving drive. Repeat for slot 2.
6. Pack the 32-bit torque setpoint. Because each SINAMICS Link slot is 16 bits, the 32-bit torque setpoint must be assembled on the receiver. The standard technique is to send the high word in slot N and the low word in slot N+1 on the source CU, then use a small DCC chart on the receiver to combine them into a 32-bit connector before routing it to p1503 (CI: torque setpoint, supplementary) or to the override input of the speed controller output. Confirm the scaling reference is consistent: both CUs should use the same p2003 value to avoid unit mismatch.
7. Download and persist. Download the configuration to both CUs. Execute Copy RAM to ROM on each so the SINAMICS Link activation survives a power cycle.
8. Verify the telegrams. In STARTER, open the trace or the online watch for the source connector on CU #1 and the corresponding receiver connector on CU #2. Force a small torque setpoint on CU #1 (e.g. via a fixed setpoint in p2200) and confirm it appears on CU #2 with the expected scaling and sign.

8. Commissioning OALINK — Step-by-Step

OALINK is documented in detail in SIOS entry 109477831 and SIOS entry 109475385. The high-level commissioning procedure is:

1. Confirm firmware. Both CUs must run SINAMICS V4.7 SP2 or later. Read the firmware version on the CU with r0018 in the expert list, or via the STARTER online diagnostics overview.
2. Verify the Drive-CLiQ ring. Both CUs must be visible to each other on the Drive-CLiQ topology. If the CUs sit in physically separated cabinets, bridge them with a DRIVE-CLiQ Hub (DMC20) or a DRIVE-CLiQ Coupling cable. The maximum cable length is 100 m on a single segment; refer to the SINAMICS S120 Equipment Manual for the exact topology rules.
3. Load the OALINK application. In STARTER, open the OA-Application slot of CU #1 and load the OALINK runtime (or a user DCC chart that calls the OALINK function blocks). Repeat on CU #2.
4. Configure the OA topology. Assign one CU as the OALINK master, the other as the slave. Set the cycle time base (125 µs or 250 µs) to match the active current-controller sampling rate on both drives.
5. Map the 32-bit torque setpoint. Connect the 32-bit torque setpoint from the source drive to the OALINK send buffer on the source CU, and from the OALINK receive buffer to the torque setpoint input of the receiving drive. Pay attention to the scaling reference (p2003) on both sides.
6. Download and restart the OA runtime. Download the OA configuration to both CUs. Power-cycle the CUs (or restart the OA runtime) to bring the OALINK up cleanly. The new firmware activation is only effective after a restart.

OALINK is the right answer if the customer wants the additional Ethernet cable eliminated and the engineering team is comfortable with DCC / OA programming. For a first-time integration with two cabinets, SINAMICS Link is usually the path of least resistance.

9. Topology Diagram — Two CU320-2 PN with SINAMICS Link

10. Verification Checklist

After commissioning, run through the following checks before releasing the system to production. Each item is a single observation that the engineer can make from the STARTER / Startdrive online view.

• Both CUs report SINAMICS Link active in the diagnostic buffer. No F08501 or F08502 entries are present.
• The link status word on the trace shows continuous bus activity on every 16-bit slot in use.
• A forced torque setpoint on CU #1 (e.g. p2200 with a fixed value) produces the expected mechanical response on the drive connected to CU #2, with the correct sign and magnitude.
• Removing the Ethernet cable between the two X140 ports (SINAMICS Link) — or the Drive-CLiQ bridge cable (OALINK) — produces the expected fault on the receiver side and a controlled stop. The fault is reset cleanly when the cable is reconnected.
• The link survives a CU power cycle: Copy RAM to ROM was executed on both CUs, and on the next start-up the link is active without a fresh download.
• The receiver BICO input (e.g. p1503) shows the expected N2 value with the same p2003 torque reference as the source.

11. Common Fault Codes and Remedies

The following fault and alarm codes are the most common entries seen during SINAMICS Link commissioning. The full list is published in the SINAMICS S120 List Manual.

12. Frequently Asked Questions