SIMOTION D vs S7-300 with SINAMICS S120 CU320-2: Motion Control

Architecture Overview: Two Paths to Multi-Axis Servo Control

When designing a multi-axis servo system with SINAMICS S120 drive components, engineers face an early architecture decision: pair the S120 cabinet with a separate SIMATIC PLC plus a CU320-2 control unit, or consolidate the PLC, motion control, and drive intelligence into a single SIMOTION D controller. Both architectures are field-proven, both can drive 1FK7 synchronous servo motors through Single Motor Modules, and both can be configured inside the TIA Portal. The decision hinges on axis count, synchronization complexity, programming style, and lifecycle cost. This reference compares the two architectures using a documented S120 configuration: an S7-300 CPU 315-2DP, a CU320-2 control unit, a 16 kW Smart Line Module, five Single Motor Modules, and five 1FK7 servo motors.

Reference Configuration and Component Identification

The reference project assembles a complete SINAMICS S120 booksize drive line-up, controlled by a SIMATIC S7-300 CPU 315-2DP. The components are:

The CU320-2 acts as the central drive controller for the S120 line-up. It hosts the drive firmware, manages DRIVE-CLiQ communication to the Smart Line Module and each Motor Module, and exposes the S120 as a PROFIBUS DP slave to the CPU 315-2DP. Each Motor Module in turn controls one 1FK7 servo motor through a DRIVE-CLiQ cable. The PLC handles the application sequence, while the CU320-2 executes the position, velocity, and current control loops for every connected axis.

CPU 315-2DP Role

The 6ES7315-2AH14-0AB0 (CPU 315-2DP) provides the PROFIBUS DP master interface, the application program in STEP 7, and the I/O scanning. The PLC transmits positioning commands to the CU320-2 over PROFIBUS using standard telegram types (typically telegram 1, 2, 3, or 105 for positioning) and reads back actual position, velocity, and status words. HMI and I/O exchange is handled in the same controller.

Decoding the SINAMICS S120 Order Numbers

Decoding the order numbers clarifies the system capability before any software is loaded:

• 6SL3130-6TE21-6AA3 — Smart Line Module 16 kW, 6-pulse, internal air cooling, with regulated DC bus and line-side thyristor precharge. Supports regenerative feedback into the supply.
• 6SL3120-1TE15-0AA3 — Single Motor Module 5 A, booksize format, internal air cooling, output for one servo motor at 3 AC 400 V.
• 6SL3120-1TE21-0AA3 — Single Motor Module 9 A, booksize format, internal air cooling.
• 1FK7060-5AF71-1DA0 — 1FK7 compact servo, 1.48 kW, 4.70 Nm continuous stall torque, 63 mm axis height, with absolute encoder (multi-turn, 22-bit).
• 1FK7083-5AF71-1DG0 — 1FK7 high-inertia servo, 3.30 kW, 10.50 Nm, 80 mm axis height, with absolute encoder and shaft seal.

Each Single Motor Module pairs with one 1FK7 motor via a pre-fabricated MOTION-CONNECT DRIVE-CLiQ signal cable. The encoder is read through the DRIVE-CLiQ interface, eliminating the need for separate encoder cables back to the CU320-2.

SIMOTION D Architecture Overview

The SIMOTION D platform is a single hardware module that combines the functions of an S7-300 / S7-400 PLC, a CU320-2 drive controller, and a high-performance motion controller. The SIMOTION D4x5-2 series embeds the PLC runtime, the SIMOTION kernel, and the drive intelligence for a connected SINAMICS S120 line-up in a single rack-mounted device. The result is a smaller cabinet footprint, fewer PROFIBUS / PROFINET nodes, and one engineering tool (SCOUT, optionally integrated in TIA Portal V20) for the entire application.

SIMOTION D variants relevant to this comparison:

The D455-2 is the direct replacement candidate for the S7-300 + CU320-2 architecture in machines that need electronic gearing, cam profiling, or cross-axis synchronization at sub-millisecond cycle times. For a step-by-step configuration of a D455-2 DP/PN with a CU320-2 PN over PROFINET IO, see the official TIA Portal SCOUT device configuration guide.

What Integrated Means in Practice

SIMOTION D removes the boundary between PLC and drive. The same project tree contains the PLC program, the axis configuration, the cam editor, and the SINAMICS S120 drive parameters. The TO (Technology Object) axis block compiles directly with the PLC code; there is no PROFIBUS telegram mapping table to maintain. The drive firmware in the S120 line-up remains the standard SINAMICS V5.x, but the configuration download is orchestrated from SCOUT.

Functional Comparison: Single-Axis Position vs Synchronization

The two architectures answer different motion problems. The S7-300 + CU320-2 combination delivers a strong single-axis position controller; SIMOTION D adds native multi-axis synchronization as a first-class function.

In the documented project, all drives run in sequence, single axis only — a classic point-to-point application. The S7-300 + CU320-2 combination is fully capable: the engineer programs a sequential startup in STEP 7, selects traversing block 1, then 2, then 3 inside the CU320-2, and reads the MELDW.3 acknowledgment bit. SIMOTION D would handle the same task but at higher hardware cost and with a steeper commissioning curve.

Programming Environments: STEP 7 vs SIMOTION SCOUT

The two stacks are configured in different tools. The S7-300 + CU320-2 path is a two-tool workflow: STEP 7 V5.5 (or TIA Portal with S7-300 plug-in) for the PLC, and STARTER or SCOUT for the SINAMICS S120 commissioning. The SIMOTION D path consolidates both into SCOUT (and, since TIA Portal V18/V20, optionally into the TIA Portal SCOUT plug-in).

The MCC (Motion Control Chart) language in SIMOTION is a flowchart-style editor designed for sequencing motion commands. Engineers transitioning from a STEP 7 GRAPH sequence often find MCC more direct for axis coordination. LAD, FBD, and ST remain available inside SIMOTION D for non-motion logic.

Typical SIMOTION D Sequence in MCC

// SIMOTION D MCC example: sequential single-axis positioning
PROGRAM MAIN_SEQUENCE
  IF bStartSequence THEN
    Axis1._MOVE(Position := 200.0, Velocity := 100.0, Acceleration := 50.0);
    WAITFOR Axis1._Status.State = STATE_HALT;
    Axis2._MOVE(Position := 50.0, Velocity := 80.0, Acceleration := 40.0);
    WAITFOR Axis2._Status.State = STATE_HALT;
    bStartSequence := FALSE;
  END_IF;
END_PROGRAM

The equivalent S7-300 + CU320-2 flow requires a STEP 7 FB that triggers traversing block selection on the CU320-2 via PROFIBUS (STW1 bit 13 = 1, STW1 bits 14-15 select block 0..63) and polls the MELDW.3 acknowledgment. The same physical movement takes more code in the PLC + drive split.

Communication Architecture and Telegram Mapping

The reference project uses CPU 315-2DP and therefore PROFIBUS DP at 12 Mbit/s. The CU320-2 in the S120 line-up is a PROFIBUS slave (with a CBP2 or CBE20 communication board depending on variant). SIMOTION D4x5-2 DP/PN variants offer both PROFIBUS DP and PROFINET IO; the -PN suffix exposes an integrated PROFINET interface with two ports (switch) on the SIMOTION D device itself.

For the documented 5-axis system with 16 kW SLM, PROFIBUS DP is fully sufficient. The bus load for 5 telegram 105 frames (servo) at 4 ms cycle is well under 30%. The switch to PROFINET is justified only if IRT synchronization between drives (sub-1 ms) or wider topology is required.

PROFIBUS Telegram Selection

For a 1FK7 servo on a CU320-2 controlled by an S7-300 or SIMOTION D, the standard telegram choices are:

For SIMOTION D integration, select Telegram 105 in the S120 drive configuration. The PZD map assigns STW1 (control word 1) and STW2 to the first two input words, with NSOLL (position setpoint), NIST (actual position), and G1_ZSW (status word) mapped into the remaining words. MELDW (message word) and POS_ZSW (position status word) provide the bit-level handshake the SIMOTION axis expects.

Parameter Read/Write via DPV1

To read or write individual S120 parameters from the S7-300, use the DPWR_DAT / DPRD_DAT pattern over PROFIBUS DPV1:

// S7-300 SCL: read r2560 (following error) from CU320-2
wDB  := 100;       // DP slave diagnostic address
wPKE := 16#1000 + 2560;  // read request for parameter 2560
wIND := 0;          // parameter index 0

// Issue DPV1 write with PKE/IND/PWE; poll DONE bit, then
// DPRD_DAT on the same slot to retrieve the 4-word response.
iRet := DPWR_DAT(LADDR := wDB, RECORD := wPKE_AND_IND_AND_PWE);

Axis Capability and Cycle Times

The CU320-2 in the documented S120 line-up supports up to 6 servo drives (12 V/f) in one control unit. The D4x5-2 SIMOTION variants do not change the underlying SINAMICS S120 limit; the S120 cabinet can be reused identically, the difference is the controller sitting on top.

The drive-side current and speed loops always live in the SINAMICS firmware; they are unchanged by the choice of controller. The position loop sits at the SIMOTION D level (or inside the CU320-2 in the legacy split). For high-bandwidth, multi-axis coordination, SIMOTION D owns the position loop and achieves tighter cross-axis coupling than the PLC + drive split.

System Topology

The two architectures map onto different physical topologies. In the S7-300 + CU320-2 reference, the PROFIBUS cable runs from the CPU to the CU320-2, and DRIVE-CLiQ fans out from the CU320-2 to the Smart Line Module and the five Single Motor Modules.

With SIMOTION D4x5-2, the CPU 315-2DP and the CU320-2 are replaced by a single SIMOTION D module in the same rack. The DRIVE-CLiQ, SLM, and 1FK7 motors remain physically unchanged. On PROFINET, the SLM and the Motor Modules connect to the SIMOTION D -PN port as PROFINET IO devices.

When to Choose SIMOTION D

Use the following decision matrix for projects that start as a simple S7-300 + S120 architecture but are heading toward synchronized motion:

1. Electronic gearing or camming required — Choose SIMOTION D. The _gear, _cam, and _add (additive setpoint) commands in MCC are a fraction of the equivalent STEP 7 + S120 logic.
2. Cross-axis register, mark correction, or print-mark synchronization — Choose SIMOTION D. The _measInput and _cam commands handle this natively.
3. Line-shaft or virtual master — Choose SIMOTION D. The virtual master is a built-in Technology Object.
4. Path interpolation (X-Y-Z coordinated motion) — Choose SIMOTION D with the path object. Not possible on CU320-2 alone.
5. More than 6 axes, deterministic cycle below 1 ms — Choose SIMOTION D. The D455-2 supports 64 axes and 0.5 ms IPO.
6. Simple sequential single-axis point-to-point — Stay with S7-300 + CU320-2. Lower hardware cost, lower training cost, faster commissioning.
7. Mix of motion and large non-motion PLC program — Either architecture works, but S7-300 + CU320-2 keeps the motion and PLC code in familiar editors.

Migration Path and Commissioning

Migrating from S7-300 + CU320-2 to SIMOTION D is incremental, not a rip-and-replace. The cabinet layout, the S120 line-up, the line filter, the line reactor, the Smart Line Module, and the 1FK7 motors all stay. Only the controllers change.

1. Hardware exchange — Remove the CPU 315-2DP and the CU320-2. Install the SIMOTION D4x5-2 in the same rack footprint. The D425-2 and D435-2 use the S7-300 200 mm rail mount; the D445-2 and D455-2 use 300 mm.
2. Wiring review — PROFIBUS DP master moves into the SIMOTION D -DP variant. PROFINET IRT can replace DP if the CU320-2 is replaced with a CU320-2 PN (CBE20 plugged in). DRIVE-CLiQ from the S120 modules to the SIMOTION D -DP/PN remains unchanged.
3. Project conversion — Import the S120 commissioning archive (created in STARTER or SCOUT) into the new SCOUT project. The S120 drive parameters carry over.
4. PLC logic port — STEP 7 LAD and FBD translate cleanly to SIMOTION D LAD and FBD. ST and SCL are virtually identical. GRAPH sequences are typically re-implemented in MCC for motion segments.
5. Commissioning checklist:
   • DRIVE-CLiQ topology correctly auto-detected (all Motor Modules green)
   • Encoder values match the mechanical position
   • Limit switches tested in software (SW-limit) and hardware (HW-limit)
   • Safe Torque Off (STO) wired through the SIMOTION D -PN/DP safety channel or a separate SIRIUS safety relay
   • EMC grounding per SINAMICS S120 booksize manual
6. Acceptance test — Run each axis individually under jog, then under MDI, then under the full MCC sequence with reduced velocity. Confirm MELDW.3 (acknowledgment) and POS_ZSW.0 / .1 / .2 bits.

For the exact steps in TIA Portal V20 — drag a SINAMICS S120 CU320-2 PN from the catalog folder Controller > SIMOTION > SIMOTION drives > SINAMICS S120, drop it into the network view, and connect it to the SIMOTION D -PN port — see the official TIA Portal SCOUT device configuration guide.

Diagnostic and Fault Handling

Both architectures expose the S120 diagnostic buffer, but the access path differs.

Common SINAMICS S120 faults to expect during commissioning of a 1FK7 / 6SL3120 line-up:

• F30002 (DC bus overvoltage) — check Smart Line Module 6SL3130 firmware version, verify line filter 6SL3000-0BE21-6DA0 grounding.
• F31117 (encoder error) — confirm DRIVE-CLiQ cable pinout, replace if damaged.
• F07900 (drive: motor blocked) — tune p2175 (motor blocked speed threshold) and p2177 (motor blocked delay).
• A30016 (load supply switched off) — verify 24 V to the Motor Module from the SLM.

Common SIMOTION D4x5-2 faults:

• 20002 (axis not homed) — execute _homing command before _MOVE.
• 20005 (axis not enabled) — set Axis._Enable := TRUE and confirm drive enable (STW1.0).
• 20130 (cam not interpolated) — verify IPO cycle is shorter than the interpolation step size.

Troubleshooting Matrix

Lifecycle and Spare-Part Considerations

The S7-300 platform entered the phase-out announcement window in 2023, with delivery subject to availability through 2028 in many regions. SIMOTION D4x5-2 DP/PN is currently in active sale and is positioned as the strategic migration path. New greenfield projects that anticipate synchronized motion should design in the D4x5-2 from the start. Existing S7-300 + CU320-2 installations are still serviceable and supported with spares through the announced phase-out window. The SINAMICS S120 booksize platform itself (the line-up used in the reference project) remains a current product and is reused unchanged in SIMOTION D applications.

When buying spare Motor Modules for a SIMOTION D migration, confirm the DRIVE-CLiQ firmware version is compatible with the SIMOTION SCOUT version. A Motor Module running older firmware than the SCOUT expects will fail to commission and emit a topology error at download. The minimum recommended SINAMICS S120 firmware for SIMOTION D4x5-2 DP/PN is V5.2 SP3, with V5.3 or later preferred for new projects.

Frequently Asked Questions