Problem Statement
A new fleet of six identical SINAMICS S120 drive systems, each built around a SIMOTICS 1FK7105-5AF71-1PA3 synchronous servo motor and a SINAMICS S120 CU320 Control Unit, cannot establish a working online connection from the STARTER commissioning tool (or the TIA-portal-bound Scout variant) when an engineer opens a backup taken from the S7-300 PLC project. The drive is visible in the STEP 7 hardware catalog and the CU320 node appears in the PROFIBUS topology, but the motor — and in some cases the entire drive object — is marked as not identified, the online/offline compare dialog stays empty, and Load to target device fails with a topology error. Because the issue reproduces on six brand-new units, the root cause is not a single defective component but a configuration or wiring pattern that has been replicated across the line.
System Reference Configuration
Understanding which component owns which data is the first step in any recognition failure. The reported architecture is:
| Component | Role | Identification in Project |
|---|---|---|
| SIMOTICS 1FK7105-5AF71-1PA3 | Permanent-magnet synchronous servo motor, shaft height 100, high-inertia variant | Visible in STEP 7 hardware as a downstream drive, in STARTER as a Servo drive object |
| SINAMICS S120 CU320 (or CU320-2 DP) | Central control unit for the S120 drive line-up; aggregates Motor Modules and I/O via DRIVE-CLiQ | PROFIBUS slave on the S7-300 network |
| SIMOTION / SINAMICS Motor Module (e.g. Double Motor Module) | Power section that drives the 1FK7 | Connected to the CU320 via DRIVE-CLiQ |
| SIMATIC S7-300 CPU 315-2 PN/DP | Higher-level PLC; PROFIBUS DP master | PROFIBUS address 2 (typical) |
| STARTER / Scout | Commissioning and diagnostics tool | Access point routing through CP5512, CP5711, PC USB-PROFIBUS, or Ethernet PN |
Root Cause Matrix
For this specific symptom — backup opens but motor/drive is not recognized — six field-proven root causes explain the overwhelming majority of incidents. Diagnose in the order listed; each step is faster and less invasive than the next.
| # | Root Cause | Symptom in STARTER/Scout | Verification |
|---|---|---|---|
| 1 | Wrong PG/PC access point in STARTER (PROFIBUS vs. S7ONLINE routing) | Target device grayed out; Accessible node empty | Set S7ONLINE (STEP7) -> PROFIBUS or Device access point matching the CP |
| 2 | PROFIBUS address mismatch between STEP 7 and the CU320 DIP switches / p0918 | CU320 visible in HW Config but absent from STARTER online scan | Compare STEP 7 slave address with p0918 and the address switches on the CU320 |
| 3 | Drive object is offline / not inserted in STARTER project | Topology tree missing the Servo or Vector DO | Insert drive object manually (Insert Drive Object) or load factory defaults |
| 4 | DRIVE-CLiQ wiring error (Motor Module or Sensor Module) | Motor LED on CU320 red, A-component state fault | Run Commissioning -> Topology in STARTER and inspect the diagnostic buffer |
| 5 | Firmware on CU320 is newer/older than STARTER supports | Online button stays disabled, version mismatch banner | Check Drive unit version vs. STARTER version, upgrade/downgrade one side |
| 6 | Electronic nameplate could not be read (DQI/EnDat fault) | Drive object present but motor type = not configured | Execute Motor data identification (p1911 / p1900) and confirm p0300 / p0301 values |
Step 1 — Confirm the Physical and Logical PROFIBUS Path
The 1FK7105-5AF71-1PA3 is a low-voltage three-phase permanent-magnet servo motor rated for inverter operation only. It is not connected to the fieldbus directly; the CU320 sits on PROFIBUS, and the motor is wired to the Motor Module over power terminals. Therefore "motor not recognized" almost always means the drive object that owns the motor was not discovered on PROFIBUS, not that the motor itself failed to talk.
- Open STEP 7 HW Config. Confirm the CU320 is configured with the correct GSD file: SIEM8170.GSD for a CU320 DP, or the PROFINET version GSDML-Vx.x-Siemens-Sinamics-S120CU320PN-yyyymmdd.xml for CU320-2 PN. Using the wrong GSD is the single most common reason a Sinamics node is visible in the PLC hardware catalog but invisible to STARTER online access.
- Read the PROFIBUS slave address from HW Config (typical values 3-15 for an S120 CU320) and physically verify the same value on the address switch of the CU320, or in the drive parameter
p0918[0]if the address is set via software. - Use the S7-300 CPU 315-2 PN/DP integrated DP master (MPI/DP port, X2) to scan the bus. In HW Config, select PROFIBUS -> Master system -> Accessible nodes. The CU320 must appear with its slave address. If it does not, the bus is broken at the connector, shield, or terminator level and no software fix will help.
Step 2 — Configure the STARTER / Scout Access Point Correctly
STARTER uses a separate access point chain from STEP 7. A typical misconfiguration is to leave the access point on TCP/IP -> Network card while the project archive specifies S7ONLINE (STEP 7) -> PROFIBUS. The result is that STARTER opens the backup offline and the online tree shows no devices.
- Close STARTER. Open Start -> SIMATIC -> SIMATIC Manager -> Set PG/PC Interface (or Control Panel -> PG/PC Interface on modern Windows).
- Select the access point that matches your cabling:
- USB-PROFIBUS adapter (CP5711, CP5512): S7ONLINE (STEP 7) -> PC USB-PROFIBUS Adapter
- Direct PROFIBUS cable on a CP5622/CP5623: S7ONLINE (STEP 7) -> CP5622/CP5623 PROFIBUS
- Ethernet PROFINET access: S7ONLINE (STEP 7) -> Network card (TCP/IP)
- Onboard MPI/DP of the CPU 315-2 PN/DP: S7ONLINE (STEP 7) -> MPI/DP
- Open the S7 project, right-click the drive in the component view, and select Target device -> Online -> Accessible nodes. The CU320 should appear at the configured slave address.
- If no node is found, run Accessible nodes with the broadcast address and confirm the bus is alive. A green box per node means the CU320 is talking PROFIBUS but STARTER is still pointed at the wrong access point if the device shows as unclassified rather than CU320.
Step 3 — Insert the Drive Object and Load the Correct Topology
The CU320 hosts multiple Drive Objects (DO) in software. A CU320 DP typically supports 1 Control Unit, up to 6 Servo or 6 Vector drive objects, plus 8 Terminal Modules. If the backup was exported at a time when the engineer had partially deleted a Servo DO, the offline project contains a drive object that the real CU320 does not have, and Load to target device aborts with F01317 "Topology comparison failed".
- Right-click the CU320 in the STARTER project tree and choose Insert drive object. Select Servo for the 1FK7 synchronous motor.
- Assign the DO to the correct DRIVE-CLiQ port of the Motor Module (typically port X5 on a Double Motor Module). Topology mismatch is the dominant cause of Unknown component at this stage.
- For each drive object, run Commissioning -> Drive navigator -> Motor identification -> Automatic identification. The SINAMICS S120 will energize the Motor Module briefly to measure the encoder offset, commutation angle, and stator resistance. The 1FK7105 has an absolute EnDat encoder, so p0400 = 2 (encoder type = EnDat) and p0401 = 8192 or 16384 depending on resolution must match the encoder type plate.
- Save the project to the PG, then perform Target device -> Load to target device -> Save to EEPROM. The motor type, encoder configuration, and electronic nameplate are written to the CU320 CF card.
Step 4 — Check the Motor Electronic Nameplate and DRIVE-CLiQ
SIMOTICS 1FK7 motors are factory-commissioned with their motor and encoder data stored in the encoder memory. STARTER reads this when the DRIVE-CLiQ link between the Motor Module (or a Sensor Module Cabinet-mounted SMCxx) and the motor is intact. Verify:
| Parameter | Expected Setting for 1FK7 with EnDat | Meaning |
|---|---|---|
p0300 |
2 (synchronous servo motor) | Motor type |
p0301 |
auto, or motor code (e.g. 1FK7xxx) | Motor code from the electronic nameplate |
p0304 |
Rated voltage (from nameplate) | Line-to-line RMS voltage of the motor |
p0305 |
Rated current (from nameplate) | Motor rated current |
p0307 |
Rated power (from nameplate) | Mechanical rated power |
p0311 |
Rated speed (from nameplate) | Mechanical rated speed |
p0400 |
2 (EnDat absolute encoder) | Encoder type |
p1911 |
Execute and wait for completion | Automatic motor data identification |
If p0301 is 0 or 9999, the CU320 did not read the electronic nameplate. The most common cause on a brand-new 1FK7105 is a missing or loose DRIVE-CLiQ cable between the Sensor Module and the motor, or a Sensor Module that is not configured (e.g. an SMC10 paired with an EnDat 2.1/2.2 encoder that requires an SMC20). Re-seat the DRIVE-CLiQ cables, then re-run Load to target device.
Step 5 — Firmware and Software Compatibility
STARTER and the CU320 firmware must be within a compatible band. Typical S120 firmware trains in the field are V4.x, V5.x, and V6.x. A V5.2 CU320 with STARTER V5.1 SP1 will refuse to read the device's online configuration; the symptom is an empty Accessible nodes list even though the bus scan in STEP 7 finds the slave.
- Read the firmware version on the CU320: Parameters -> r0964 displays the current SINAMICS firmware version.
- Match the STARTER version: Help -> About -> STARTER shows the version, and the Installed software tab in the project tree shows the target firmware.
- If a mismatch is found, either upgrade STARTER (the newer tool supports older firmware) or request the firmware version of the CU320 CF card from Siemens Support. Do not downgrade firmware on a brand-new unit without confirming the Motor Module can accept the older version.
Step 6 — Six-Unit Fleet Commissioning Pattern
When six identical cabinets are commissioned in sequence, the fastest path is to fully commission the first unit, save the project, then use Load to target device -> Restore factory settings + load on the remaining five. This produces a uniform image on every CF card and isolates the failure mode: if five out of six commission cleanly, the failing one has a hardware issue (typically a backplane connector, DRIVE-CLiQ cable, or a missing terminating resistor on the PROFIBUS drop). If all six fail in the same way, the problem is in the project, the GSD, or the access point — not the drives.
Verification Procedure
- After Load to target device, the CU320 diagnostic LEDs should show:
- RDY (green, steady) — control unit ready
- DP (green, blinking) — PROFIBUS cyclic communication
- For the 1FK7 drive: Drive object online and Servo enable = no faults in the STARTER fault buffer.
- Check the drive's fault buffer (Diagnostics -> Faults/warnings). Expected result: no active faults.
- Open Control panel in STARTER, enable the drive at low speed (≤ 50 rpm), verify encoder feedback actual speed value matches speed setpoint.
- Run Trace on p0015 (drive configuration) and r0020 (speed setpoint smoothed) for at least 2 s to capture a controlled acceleration profile.
- From the S7-300 CPU 315-2 PN/DP, request a free telegram 1 / standard telegram 5/6 (depending on the S120 firmware) and confirm the cyclic PROFIBUS frame is exchanged with the CPU at the configured bus cycle time.
Frequently Asked Questions
Why does STARTER see the CU320 in the project tree but not online?
The PG/PC access point is set to a different interface than the one physically connected. Open Set PG/PC Interface and select S7ONLINE (STEP 7) -> PROFIBUS for a CP5622/CP5711, or TCP/IP -> Network card for a PROFINET CU320-2 PN. Re-opening the project tree after the access point change forces STARTER to re-scan through the correct adapter.
The motor nameplate does not match p0300 in the drive object. Which one is correct?
For a 1FK7 synchronous servo, set p0300 = 2 (synchronous motor) and either accept p0301 from the electronic nameplate read, or enter the motor code from the type plate (e.g. 1FK7105-5AF71-1PA3). The nameplate do not override these — the parameters must match the motor you have physically wired, otherwise the regulator constants and torque limits will be wrong.
Is PROFIBUS DP or PROFINET the right bus for a CU320-2 in this architecture?
Both are supported. A classic CPU 315-2 PN/DP pairing with a CU320-2 DP uses PROFIBUS DP at 1.5 or 12 Mbit/s, with the CU320 acting as a slave. A CU320-2 PN on PROFINET gives the same cyclic and acyclic services, plus a cleaner migration path to TIA Portal. Functionally, the choice has no impact on whether STARTER recognizes the drive — the GSD/GSDML and the access point must both be consistent.
The DRIVE-CLiQ port LED on the Motor Module is red after a power cycle. What next?
A red DRIVE-CLiQ LED indicates either a wiring error or a component mismatch. Check the cable to the Sensor Module and the motor, confirm the Sensor Module (SMC10/SMC20/SME) is the one Siemens lists for the 1FK7105 encoder, then re-seat and re-power. If the LED stays red, run Topology in STARTER to view the offline compare against the online scanned topology; the diagnostic buffer entry F01317 will name the missing or wrong component.
Can I bypass STARTER and configure the SINAMICS S120 from TIA Portal instead?
Yes, for a CU320-2 PN with the Startdrive add-in or for SIMOTION D4xx with Scout in TIA. For a classic CU320 DP, the supported path is still STARTER. Mixing tools (commissioning the drive in TIA, then trying to read it from STARTER) is the most common source of "project not recognized" errors in mixed-version plants, so commit to one toolchain per fleet.