Replacing SINAMICS S120 DMM with SMM in TIA StartDrive

Problem Statement

A common engineering change in a SINAMICS S120 line-up is the swap of a Double Motor Module (DMM) for a Single Motor Module (SMM) when only one physical axis is actually wired and the freed telegram slots are needed for other I/O in the PROFINET cycle. The typical configuration is a CU320-2 PN control unit together with an S7-1500 controller, configured in TIA Portal V14 with the S120 StartDrive option package installed.

The intuitive question is: can the existing DMM object be edited in place, simply re-typed as an SMM, while keeping the motor data, encoder data, closed-loop parameters and the PZD mapping? The verified answer from Siemens application support is no: a DMM cannot be converted into an SMM in place, and the motor / encoder drive objects must be re-created from scratch. The same restriction applies in the opposite direction: an SMM cannot be silently expanded into a DMM without data loss.

SINAMICS S120 Motor Module Topology: SMM vs. DMM

The SINAMICS S120 booksize / blocksize line-up supports two physically different motor-module form factors that share the DRIVE-CLiQ backplane but expose different drive-object counts and different current ratings.

Because the DMM materialises two drive objects on the CU320-2, the PROFINET telegram configuration allocates two PZD containers. When the DMM is removed and replaced by an SMM, only one telegram remains — the second PZD block is freed up, which is precisely the byte budget that the engineer in the source case wanted to reclaim for additional I/O.

Why Direct DMM → SMM Replacement Is Not Supported

The SINAMICS commissioning environment (STARTER classic and StartDrive in TIA) models the S120 line-up as a tree of drive objects (DOs). The DO tree contains:

• The Control Unit DO (CU320-2 in this case).
• Optional Line Module DOs (Active Line Module / Smart Line Module / Basic Line Module).
• One DO per Motor Module axis: an SMM produces one DO; a DMM produces two DOs (commonly numbered consecutively as Axis_1 / Axis_2).
• Each DO carries its own telegram assignment, PZD extension, safety slot (if used) and a dedicated parameter image (motor data p2900 ff., encoder data p2500 ff., controller data p1400 ff.).

When you change the motor-module catalog entry from DMM to SMM, the tool would have to:

1. Drop one of the two drive objects that was instantiated by the DMM.
2. Re-index all subsequent DO numbers (everything downstream renumbers).
3. Recompute the PROFINET / PROFIdrive telegram mapping table that the S7-1500 reads via SINA_PARA or direct PZD access.
4. Shift all symbolic I/O addresses in the PLC project, breaking every %IW / %QW reference and HMI tag binding.

StartDrive cannot guarantee a consistent result across all four steps without re-running the full Configure drive wizard, which is why the only supported workflow is a delete-and-reinsert.

Affected Versions and Configuration Packages

The restriction is implemented at the StartDrive configuration layer and is not firmware-version dependent, so the procedure below is valid for both V4.x and V5.x SINAMICS firmware generations.

Pre-Replacement: Backup Strategy

Because drive parameters, the DO tree and telegram mapping are all about to be rebuilt, take the following backups before touching the device configuration:

1. TIA project archive. Project → Archive… → select PC archive. Save the .zap14 file to a versioned location (e.g. project_2024-04-12_pre-DMM-to-SMM.zap14).
2. Drive parameter backup via StartDrive. Online → select the CU320-2 → Drive → Commissioning → Backup / restore → Upload to PG. This produces a parameter archive tied to the device serial number.
3. STARTER-style .par backup (if the project was originally commissioned in STARTER): Commissioning → Save to memory card and Load to PG.
4. S7-1500 program archive: CPU → Download to device → Archive if any recipe / technology data lives in the PLC rather than in the drive.
5. Export the symbolic I/O list from the PLC tags so telegram offsets can be re-applied after the swap.

Procedure: DMM → SMM Conversion in TIA Portal V14 (StartDrive)

There is no single-click conversion. The workflow is a delete-and-reinsert followed by manual parameter restoration and PLC-side address updates.

1. Open the project offline. In the TIA project tree, expand Devices & networks → CU320-2 PN → Drive objects.
2. Document the current state. Note the DO numbers of the two DMM axes, their telegram numbers, PZD lengths and slot addresses. Example record:

   DO 3  SERVO   Telegram 105  PZD-in 12 / PZD-out 6   Slot 0  Base  256
   DO 4  SERVO   Telegram 105  PZD-in 12 / PZD-out 6   Slot 0  Base  272

3. Disconnect the PLC tags. Open the PLC tag table used for telegram data and either delete or rename the affected tags so they become available for re-binding after re-insert.
4. Delete the DMM. Right-click the DMM entry in the topology → Delete device. Confirm that StartDrive will also remove its two drive objects. Tick Also delete associated drive objects if the dialog offers it.
5. Delete the orphan drive objects. If any SERVO / VECTOR objects remain in the drive-object tree, delete them as well. The topology and the DO tree must be in a consistent empty state before re-insert.
6. Insert the SMM. In the hardware catalog, navigate to Drives & starters → SINAMICS S120 → Motor Modules → Single Motor Module. Drag the correct article number (e.g. 6SL3120-1TE21-8AA4) onto the free slot of the CU320-2 DRIVE-CLiQ line.
7. Configure the new axis. Run Configure drive on the newly inserted SMM: select the motor from the catalog (or enter motor code), assign encoder (DRIVE-CLiQ or SSI/EnDat via SMC), set control mode (Servo / Vector), select telegram (e.g. Siemens telegram 105, 106 or standard telegram 3), and confirm safety integration (Extended / Advanced / disabled).
8. Restore parameters from backup. Online → Drive → Commissioning → Restore from PG. Browse the .par / .bak archive saved in step 2 of the backup section and confirm. Note: only the single-axis parameter image is restored; the second-axis image no longer exists.
9. Compile and download the project. Right-click the S120 device → Compile > Hardware and software (rebuild all). Resolve any compilation warnings about telegram mapping. Download to the CU320-2.
10. Re-bind PLC tags. Update the tag table to point at the new telegram base address (typically the base will shift if the second DMM axis was using slot bytes after the kept axis).

Telegram Re-Mapping and I/O Address Recalculation

The PROFINET telegram slot allocation is the part of the change that most often catches engineers out. The table below shows a typical before / after for a CU320-2 PN serving two SERVO axes through a DMM (telegram 105 / 105) and then the same axis served through an SMM.

The byte saving is exactly what made the original swap attractive in the source case — the engineer wanted those bytes relocated to a different I/O region rather than reassigned to the second axis.

PLC Program Adjustments on the S7-1500 Side

After the SMM is online and the S7-1500 has downloaded the new hardware configuration, the following PLC-side changes are typically required:

• Update device references. Any FB that referenced the second axis by its hardware identifier (HWID) must be re-targeted. In TIA V14, the HWID for the deleted axis shows up as invalid in the tag table after compile; search the program for these HWID literals and clear them.
• Re-map the symbolic I/O. If the second-axis PZDs were consumed by user FBs (e.g. SINA_PARA, SINA_SPEED, SINA_POS), the unused FBs should be disabled or deleted to free PLC resources.
• Re-evaluate watchdog and OB1 timing. Removing one telegram slot reduces the PROFINET IRT frame payload; the S7-1500 PROFINET stack usually recovers automatically, but verify that the send clock (typically 1 ms / 0.5 ms) and reduction ratio are still within the configured PROFINET domain.
• Tech objects in S7-1500 Motion Control (if used). The TO_Axis / TO_SynchronousAxis / TO_ExternalEncoder associated with the deleted axis must be deleted from the technology object tree, otherwise the S7-1500 will raise Technology object configuration error (2003 / 2004) at startup.

Reverse Direction: SMM → DMM Conversion

The same restriction confirmed by Siemens application support applies in reverse. Converting an SMM into a DMM is treated as a topology addition, not a parameter change:

• The original axis keeps its DO number, motor data, encoder data and telegram mapping.
• A second drive object is created on the new DMM but starts in an un-commissioned state.
• Motor ID, encoder ID, mechanical system data and all controller parameters (current, speed, position loops) for the new axis must be entered from scratch.
• PLC-side, an additional PZD slot appears at the next free address; all subsequent tags shift and must be re-bound.

Plan a half-day to one commissioning window for the new axis including encoder adjustment (p1990), commutation-angle calibration (p1996 or automatic with encoder code), and acceptance test of any safety functions assigned to the new axis.

Verification and Re-Commissioning

1. Offline consistency check. Right-click the S120 device → Compile > Hardware (only). Expected: zero errors and zero warnings. Warnings about unused telegram slots indicate the previous DMM mapping was not fully cleaned up.
2. Topology check. Online → Devices & networks → Topology view. Verify the DRIVE-CLiQ port of the new SMM matches the physical port number (e.g. port X2.3 of the CU320-2). A mismatch produces fault F0135 (topology violation) at first power-up.
3. Online telegram check. Online → Drive object → Communication → Telegram configuration. Confirm the active telegram number and PZD length match the PLC hardware configuration.
4. Cyclic PZD test. In the S7-1500, use a watch table with the new input addresses (e.g. %IW256) and force a small setpoint. The drive should report the setpoint back in the corresponding status word without F08501 (PROFINET communication fault) or F08502 (sign-of-life timeout).
5. Safety acceptance (if PROFIsafe is in use): run the S7-1500 F-CPU acceptance test for the modified F-device list. The acceptance report must list the deletion of the prior F-device.
6. Trace recording. Capture a 5-second STARTER / StartDrive trace of the speed controller output, current setpoint and actual value. Compare against the pre-conversion trace to confirm equivalent dynamic behaviour.

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