Connecting STARTER to Sinamics S120 via 840D SL NCU 720.3 PN

Problem Overview

Engineers commissioning or servicing a SINUMERIK 840D sl controlled machine frequently need to back up the parameter sets of the integrated and external SINAMICS S120 drives. The most common path is the STARTER commissioning tool connecting to the NCU's service interface (X127) and then routing down to the SINAMICS Control Unit (CU) and Motor Modules. When STARTER cannot browse the drives under "Accessible nodes", the failure is almost always a version mismatch, a missing SINAMICS Support Package (SSP), or an incomplete STEP 7 hardware configuration in NetPro/ProTool/Pro that disables routing.

The failure case described here is representative of a 10-axis horizontal machining center built around an NCU 720.3 PN (6FC5372-0AA30-0AB0) with a SIMATIC S7 317-3 PN/DP PLC, CNC-SW 31.3 with SinOP 4.7 SP3, an NX15.3 numerical control extension (6SL3040-1NB00-0AA0), and a mix of SMM and DMM modules (6SL3120-1TE28-5AA3, 6SL3120-1TE23-0AC0, 6SL3120-2TE21-8AC0). STARTER V4.5.1.0 is installed on the service PG. The NCU reports firmware 4.07.04 on the machine, but STARTER's "Accessible nodes" shows version 4.07.35.84. The PLC connects fine on the same Ethernet cable, so the physical layer is not the problem.

Affected System Identification

Confirm the exact machine configuration before changing software. The combination of components below is the canonical test bench for this fault pattern.

When the actual machine matches this or a similar profile, the steps in the rest of this article apply. If the machine is on a different CNC-SW (for example SinOP 4.5 or 4.8 SPx) the SSP version requirement changes accordingly.

Root Cause Analysis

STARTER reaches the NCU but cannot "see" the SINAMICS drives. The three root causes that produce this exact symptom are listed below in order of probability for an in-service machine that previously commissioned cleanly.

1. Missing or outdated SINAMICS Support Package (SSP) on the CF card. The SSP must match the SINAMICS firmware version installed. Without it, STARTER cannot decode the drive telegrams and the CU never appears as a navigable sub-node in the project tree.
2. STARTER / SSP version mismatch. STARTER V4.5.1.0 was built against a specific SINAMICS firmware baseline. If the CF card's SINAMICS firmware is newer than what the STARTER SSP on the PG knows about, the "Accessible nodes" view will show a version (here 4.07.35.84) that does not match the version STARTER expects (4.07.04) and routing into the CU will be refused.
3. STEP 7 hardware configuration (HW Config) not loaded into the PLC, or the PROFIBUS subnet in NetPro missing the integrated CU. The S7 routing tables are what permit STARTER packets to traverse the NCU/PLC and reach the drive line. If the hardware configuration in STEP 7 does not include the integrated SINAMICS as a station on the internal PROFIBUS, no routing entry exists.

The 4.07.35.84 vs 4.07.04 discrepancy reported by the engineer is a textbook symptom of root cause #2: the STARTER installation on the PG carries the latest published SSP, while the machine's CF card carries a frozen service-pack version. STARTER is therefore asking the drive to negotiate a protocol variant the drive does not know.

Prerequisites

Before touching the project, confirm the following items are in place. Any missing item is itself a probable cause of the connection failure.

• STARTER V4.5.1.0 (or later 4.5.x) installed on the service PG.
• STEP 7 V5.5 SP4 or higher installed on the same PG so that the existing STEP 7 project (which contains the hardware configuration) can be opened.
• Administrator rights on the service PG to install SSP and to set the PG/PC interface.
• Set the network interface of the PG to the plant service subnet (X127 = 192.168.214.x, mask 255.255.255.0, no default gateway). Do not use the X120 PROFINET production network for commissioning traffic.
• A direct Ethernet cable (or a switch on the service network) between the PG and the NCU's X127 port.
• The original CF card image (commissioning archive / STARTUP.ARCHIVE) so the machine can be restored if anything goes wrong.

STARTER Version Compatibility Matrix

Use this matrix to choose the right STARTER / SSP pairing for the installed CNC-SW and SINAMICS firmware.

Rule of thumb: the SSP on the PG must be the same major/minor version that the machine's SINAMICS firmware was built from. Service packs are absorbed via HMI or CF-card update; cross-major versions (for example 2.x talking to 4.x) are not supported.

Step 1 - Install the Correct SINAMICS Support Package

The SSP is the integration layer that teaches STARTER how to interpret the drive objects on a 840D sl. Without the right SSP, STARTER can talk to the NCU shell but the SINAMICS sub-tree stays empty.

1. Locate the SSP for the installed CNC-SW. For CNC-SW 31.3, use the SSP shipped on the install media under \SINAMICS\SSP. For CNC-SW 31.4 / 4.8 SP2, retrieve it from the official Siemens support entry SINAMICS Support Package for 840D sl CNC-SW 4.8 SP2.
2. Close all running STARTER and STEP 7 instances.
3. Run the SSP installer on the PG. The installer places the new drive object types under the STARTER option packages and refreshes the device library used by HW Config.
4. Restart the PG to clear the COM/DCOM cache; STARTER loads device catalogs at startup.
5. Open STARTER and verify the installed version under Help → About → Installed option packages. The new SSP must appear here.

Step 2 - Match the Firmware Version on the Service PG

Even with the right SSP, the PG-side SINAMICS firmware image must equal the image burned into the CF card of the machine. The CF card is the source of truth.

1. On the HMI, navigate to Commissioning → SINAMICS → Drive system → Version overview. Record the SINAMICS FW version exactly as displayed (here: 4.07.04).
2. On the service PG, open the same SINAMICS firmware image in STARTER without going online. Compare the version string character-for-character.
3. If the versions differ, do one of the following:

• Reflash the service PG's library to the older version that matches the machine, OR
• Upgrade the machine's CF card using a service pack on a USB stick. The standard procedure is to copy the SINAMICS firmware folder from the install media to a USB stick, plug it into the HMI, and use Commissioning → SINAMICS → Firmware update to load it. This must only be done with the spindle and feeds in a safe, de-energized state.

Step 3 - Configure the PG/PC Interface for X127

The X127 service interface on the NCU 720.3 PN is a fixed 192.168.214.1/24 address, and the TCU/MCP sit on the same subnet. Configure the PG so it can be seen by all of them.

1. Open Control Panel → Set PG/PC Interface on the service PG.
2. Select the Ethernet adapter that is wired to the NCU X127 port.
3. Assign the PG a static address: 192.168.214.250 / 255.255.255.0, no default gateway. This guarantees the PG is on the same /24 as NCU (192.168.214.1), TCU1 (192.168.214.10), TCU2 (192.168.214.12) and MCP (192.168.214.11).
4. From a command prompt, ping 192.168.214.1. A reply confirms the physical layer; the engineer in this case already confirmed this with the PLC online connection, so the PG/PC interface is known to be correct.

Step 4 - Verify STEP 7 Hardware Configuration

Routing from the PG through the NCU/PLC down to the integrated SINAMICS is built on the STEP 7 hardware configuration that lives inside the STEP 7 project loaded on the PG. STARTER can only see what STEP 7 can route to.

1. Open the machine's STEP 7 project on the PG.
2. Open NetPro or HW Config.
3. Verify that the project contains, in this order: S7 317-3 PN/DP → PROFINET subnet → NCU 720.3 PN (with the integrated SINAMICS as a sub-module on the internal PROFIBUS) → NX15.3 → external SINAMICS S120 drives.
4. Verify the integrated CU is inserted under the NCU's PROFIBUS interface as a station. The integrated CU typically has PROFIBUS address 3 or 4 on the internal PROFIBUS (default in HW Config).
5. Compile and download the hardware configuration to the PLC using PLC → Download to Target System. The routing tables are written at this step.

Step 5 - Open STARTER and Configure the Online Interface

1. Start STARTER and open the existing project that matches the machine (or create a new offline project mirroring the topology).
2. Right-click the project node and choose Set PG/PC interface → ... → TCP/IP → [Ethernet adapter].
3. Right-click the project node and choose Accessible nodes. STARTER will broadcast a discovery packet on the service subnet. Expect to see the NCU appear with its IP 192.168.214.1 and the TCUs.
4. Click the small arrow to the left of the NCU entry. The integrated CU appears as a child node only if the SSP and routing are correct. If the arrow does not appear, the CU is invisible to STARTER and root cause #1, #2, or #3 is unresolved.

Step 6 - Establish Online Connection and Upload the Project

1. Right-click the integrated CU entry and choose Connect to target system.
2. Confirm the dialog. STARTER transitions the project to "online". The drive LEDs on the SMM/DMM modules stop flashing red and a green state indicator appears in the project tree.
3. Choose Target system → Load to PG (upload from device to project) to mirror the live parameter set into the offline project on the PG.
4. Save the project to the PG's local drive. This is the parameter backup independent of the STARTUP.ARCHIVE file that lives on the HMI.

Step 7 - Take the Parameter Backup (Drive-Side)

Two independent backup paths exist. For a complete protection image, do both.

For the SINAMICS-only backup using the drive's own non-volatile memory, set the following parameters on each drive object before powering off:

• p0977 = 1 - Save all drive parameters to non-volatile memory (NVRAM).
• p7760 = 1 - Activate write protection removal for the safety parameters if the drive uses Safety Integrated.
• For commissioning archive generation, use STARTER Project → Archive → Create and select the SINAMICS sub-tree. Save the .zip file with a machine-specific name and date.

Verification Checklist

Run through this list end-to-end after every change. A green on every line means the connection is healthy.

1. Ping 192.168.214.1 from the PG → reply.
2. STARTER → Accessible nodes shows the NCU at 192.168.214.1 → yes.
3. The integrated CU is visible as a child of the NCU entry → yes.
4. The version string in the project tree matches the version on the HMI's Commissioning → SINAMICS → Version overview → exact match.
5. Right-click the integrated CU → Connect to target system → transitions to online, no fault in the diagnostics buffer.
6. Right-click an SMM/DMM axis → Load to PG → parameter list populates with no "incompatible firmware" warnings.
7. STARTER Project → Archive → Create produces a valid .zip file of non-trivial size (typically 5-20 MB for a 10-axis machine).

Troubleshooting Matrix

Notes on the Internal PROFIBUS Topology

The NCU 720.3 PN has an integrated CU on the internal PROFIBUS that links to the SMM/DMM modules. The NX15.3 (6SL3040-1NB00-0AA0) extends the same internal PROFIBUS to four additional axes. The complete path is:

PG (192.168.214.250) -- Ethernet --> NCU 720.3 PN (192.168.214.1) -- PROFINET --> PLC S7 317-3 PN/DP
    |
    |-- internal PROFIBUS (1.5 Mbit/s, addr 3/4 default) --> integrated SINAMICS CU
            |--> 6 S120 axes (NCU section)
    |--> NX15.3 (6SL3040-1NB00-0AA0) --> 4 S120 axes (extension section)

Drive part-number notes for documentation purposes:

• 6SL3120-1TE28-5AA3 - 85 A Single Motor Module, Booksize, internal air cooling, 3 AC 600 V class.
• 6SL3120-1TE23-0AC0 - 30 A Single Motor Module, Booksize, internal air cooling.
• 6SL3120-2TE21-8AC0 - 18/18 A Double Motor Module, Booksize, internal air cooling (two 18 A axes in one module).

These are all members of the SINAMICS S120 Booksize family and are commissioned through the standard STARTER DCC drive object browser once routing to the integrated CU is functional.

Restoring from the Backup

To verify the backup is valid, perform a dry-run restore on a bench or a planned outage. In STARTER, Target system → Load to target system with the saved project rewrites every parameter, including p0100 (mains voltage), p0340 (motor data calculation), p2000 (reference speed), and the Safety Integrated parameters on drives that use them. Confirm after load that the HMI's Commissioning → SINAMICS → Version overview still matches the project tree and that the drives ramp up without alarm codes A30016 / A30017 (load error during commissioning).

FAQ