SINAMICS G120 CU250S-2 PN Encoder Setup in TIA Portal V14

1. Application Context and Architecture

The SINAMICS G120 is a modular low-voltage drive family. The CU250S-2 PN Control Unit adds a PROFINET interface (2-port switch, ERTEC ASIC), encoder evaluation for two physical channels, and the integrated Basic Positioner (EPOS) for entry-level positioning. The combination of a SIMATIC S7-1200 (in this case the AC/DC/RLY variant) and a SINAMICS G120 with CU250S-2 PN is one of the most common positioning architectures in laboratory, packaging, conveyor, and small-format assembly applications.

For a project with a SIMATIC S7-1200 AC/DC/RLY controlling a SINAMICS G120 CU250S-2 PN over PROFINET and an external encoder wired to the drive, two engineering paths exist. The choice depends on where the closed-loop position controller should run:

• Path A (drive-based position control): The CU250S-2 runs the closed-loop position controller through the integrated Basic Positioner (EPOS). The PLC is the higher-level motion coordinator, sending target positions, velocities, override values, and jog commands through the SINA_POS block (from the Siemens DriveLib library). The encoder feedback is read by the drive and exposed to the PLC as process data. This is the cleaner path for an entry-level positioning axis.
• Path B (PLC-based position control): The S7-1200 hosts a technology object (TO_PositioningAxis or TO_SynchronousAxis) that closes the position loop in the PLC. The drive operates as a speed-controlled actuator (telegram 1 or 3), and the technology object drives the speed setpoint. Useful when the position loop must interact directly with PLC logic, registration marks, or with other axes.

Both paths are covered below. The decision should be made before commissioning because the parameter set, the telegram selection, and the block library differ.

2. CU250S-2 Encoder Interface Topology

The CU250S-2 provides two physical encoder interfaces:

If only one encoder is connected, X9 is used. If two encoders are connected, one is used for motor speed control and the other for position feedback. The combination rules — including which encoder can be assigned to which control function — are described in the Siemens application document "Which encoder combinations can be used on the SINAMICS G120 Control Unit CU250S-2" (entry ID 109813048).

Encoder combinations for SINAMICS G120 CU250S-2 (PDF, Siemens support, 109813048)

3. Compatible Encoder Types

The CU250S-2 firmware evaluates the following encoder protocols. The maximum input frequency applies to the firmware evaluation, not the encoder's own output frequency.

Resolvers are not supported on the CU250S-2. For resolvers, use a different Control Unit family (e.g., a CU240E-2 with the appropriate option module) or a different SINAMICS drive.

For a motor-mounted incremental encoder in the 1024 to 2500 ppr range, the TTL interface on X9 is the most common choice. For SSI absolute encoders (often used in safety applications or to avoid re-homing on power-up), X9 is the only option.

4. Hardware Wiring

4.1 X9 Sub-D Pinout (TTL Incremental, the most common case)

For TTL encoders, the 5 V supply is normally generated inside the encoder from a 24 V input. The encoder's 5 V output is fed back into the drive on pins 1…6. Always verify the actual pinout against the encoder's datasheet; encoder manufacturers do not always follow a single convention.

4.2 X9 Sub-D Pinout (SSI Absolute)

For SSI encoders, the clock signals are output on pins 1/2 (CL+ / CL−) and the data is returned on pins 3/4 (DA+ / DA−). The pin numbering matches TTL, but the protocol is set in p0400 = 12 and the protocol details (clock rate, monoflop time, coding) in p0421.

4.3 X10 Terminal Pinout (HTL / TTL)

X10 is the second encoder channel and is used for an external encoder (machine feedback). It does not evaluate SSI and does not evaluate a zero mark on the terminal block side.

For full pin assignments, refer to the G120 with CU250S-2 Control Units operating instructions (PDF, Siemens support, 99730303).

5. TIA Portal V14 Project Setup

5.1 Prerequisites

The S7-1200 AC/DC/RLY designation in the question refers to the CPU power supply (AC mains input), the internal logic (DC derived from the AC), and the digital output type (RLY = relay). It does not affect the PROFINET interface or the DriveLib functionality. The exact order number of the CPU (for example, 6ES7214-1xxx40-0xB0) should be confirmed in the TIA Portal hardware catalog under "SIMATIC S7-1200 → CPU."

5.2 Project Creation and CPU Addition

1. Open TIA Portal V14 and create a new project.
2. Add the S7-1200 CPU: in the project tree, "Add new device" → "SIMATIC S7-1200 CPU" → select the actual order number from the catalog.
3. Switch to the device view of the CPU. Set the PROFINET interface (X1) IP address (for example, 192.168.0.10) and the PROFINET device name (for example, plc-1200). The device name must be unique on the PROFINET subnet.
4. Connect the CPU to a PROFINET subnet in the network view.

5.3 Adding the SINAMICS G120

Two methods are available:

• Through the TIA Portal hardware catalog (preferred): With Startdrive V14 installed, drag the SINAMICS G120 CU250S-2 PN into the network view. Set the IP address (for example, 192.168.0.20) and the PROFINET device name (for example, g120-cu250s). The PROFINET name is what the S7-1200 uses to address the drive.
• Through GSD import (fallback): Download the GSDML file for the CU250S-2 PN from the Siemens support pages. Install the GSD in TIA Portal under "Options → Manage general station description files (GSD)." The drive then appears in the catalog under "Other field devices → PROFINET IO → Drives → Siemens AG."

With the Startdrive option package, the G120 is configured directly inside the TIA Portal project. This is the recommended path because the parameter assignment, the drive commissioning, and the PLC programming are managed in the same tool, and the DriveLib blocks (SINA_POS, SINA_SPEED) are available as native project elements.

5.4 PROFINET Telegram Configuration

The standard positioning telegram on the CU250S-2 PN is telegram 111. The basic speed-control telegrams are telegram 1 and telegram 3.

In the device view of the G120, navigate to "Properties → PROFINET interface → Telegram configuration." Assign telegram 111 for the positioning path. If the encoder feedback is to be exchanged in a structured form (for example, raw pulse count alongside the position), telegram 999 (free configuration) can be used to map specific process data. For most applications, telegram 111 is sufficient.

6. DriveLib Installation

DriveLib is the Siemens library that exposes drive-specific function blocks for STEP 7 in TIA Portal. The library contains:

To install DriveLib V14:

1. Open TIA Portal V14.
2. Open the project.
3. Select "Options → Global libraries."
4. In the global library pane, click "Open global library" and navigate to the DriveLib archive (downloaded from Siemens support, entry ID 109475016 or the most recent DriveLib V14).
5. Drag the master copies of the required blocks (for example, SINA_POS, SINA_SPEED) into the project's program blocks. The FB types and the corresponding instance DBs are created.

7. SINAMICS Parameter Assignment for Encoder and EPOS

After the project is loaded into the CU250S-2 (through Startdrive online or through the drive's web server), the encoder and EPOS parameters must be set. The minimum parameter set for Path A (EPOS) is shown below.

The parameter list is intentionally minimal. For complete drive commissioning (motor identification, current controller optimization, speed controller optimization, encoder test, referencing mode), the G120 with CU250S-2 Control Units operating instructions (PDF, Siemens support, 99730303) is the authoritative reference.

The encoder combination rules — that is, which encoder is used for speed control and which is used for position feedback when two encoders are connected — are documented in the Encoder combinations for SINAMICS G120 CU250S-2 (PDF, Siemens support, 109813048). The assignment is made through p2506 (EPOS encoder) and the speed/position controller encoder selectors in the firmware.

8. Option A — EPOS in the Drive, SINA_POS in the PLC

8.1 Concept

In Path A, the closed-loop position controller is implemented inside the CU250S-2. The PLC issues high-level commands: "move to position X at velocity V using acceleration A," "jog in the positive direction," "stop," "set reference point." The drive handles the ramp generator, the position controller, the encoder evaluation, and the safety limits. The PLC receives the actual position and the status word as process feedback. This is the simpler of the two paths for an entry-level application and gives the cleanest separation between motion control (in the drive) and machine logic (in the PLC).

8.2 SINA_POS Interface (DriveLib V14, representative call)

// FB SINA_POS — DriveLib V14
// Inputs
iEnableAxis        : BOOL;   // TRUE enables the drive and the positioner
iCancel            : BOOL;   // TRUE aborts the active motion
iIntermStop        : BOOL;   // TRUE ramps to zero (intermediate stop)
iDirPos            : BOOL;   // TRUE jog / MDI positive
iDirNeg            : BOOL;   // TRUE jog / MDI negative
iAck               : BOOL;   // Rising edge clears drive faults
iExecMode          : BOOL;   // TRUE executes the MDI setpoint
iMode              : INT;    // 0 = jog, 1 = MDI relative, 2 = MDI absolute
rTargetPos         : REAL;   // Target position in length units (LU)
rTargetVel         : REAL;   // Velocity in LU/min
rAccel             : REAL;   // Acceleration in LU/s^2
rDecel             : REAL;   // Deceleration in LU/s^2
iAxisNo            : INT;    // Drive axis number (1 by convention)
iHWIDSTW           : HW_IO;  // Hardware identifier of the control word (STW)
iHWIDZSW           : HW_IO;  // Hardware identifier of the status word (ZSW)

// Outputs
rActualPos         : REAL;   // Actual position in LU
rActualVel         : REAL;   // Actual velocity
wAxisStatus        : WORD;   // Drive status word
bError             : BOOL;   // TRUE on error
wErrorID           : WORD;   // Error number

The hardware identifiers (HWIDSTW, HWIDZSW) are obtained automatically when the SINA_POS block is dropped onto the S7-1200 program and the "Call options" dialog is used to connect it to the PROFINET telegram of the G120 in the project tree. The HMI connection is configured in the same step.

8.3 STW1 (Control Word 1) Bit Pattern

EPOS is controlled by the STW1 bits. The SINA_POS block sets these bits automatically; understanding them is necessary for diagnosis.

8.4 ZSW1 (Status Word 1) Bit Pattern

8.5 Reading Encoder Data Without Using EPOS

If the application does not need closed-loop positioning — for example, if the encoder is used only for speed feedback and the position is calculated in the PLC — the actual position in EPOS units (LU) is available on the output of SINA_POS, and the actual velocity in the same block.

For raw encoder counts (pulses per revolution × gearbox ratio), the SINAMICS parameter r0481 (encoder 1 actual position, in pulses) can be read through the standard acyclic parameter read/write mechanism (PROFIdrive parameter channel, record data sets 0xB02E for read, 0xB02F for write). The PLC uses the RDREC and WRREC instructions.

A typical acyclic read of r0481 is performed with:

• Request header: function = 1 (read by parameter number), parameter number = 481, index = 0.
• Response: 4 bytes of encoder position data in big-endian order.

The full acyclic parameter channel format is in the PROFIdrive profile and the G120 operating instructions. For periodic encoder data, the cyclic process data (telegram 111 or telegram 3 with an encoder word) is more efficient than the acyclic channel.

8.6 Commissioning Sequence (Path A — EPOS)

1. Wire the encoder to X9 (or X10) following the pinout. Verify the shield is bonded at the connector backshell.
2. Power up the drive. Confirm the Control Unit is online and PROFINET is connected (LEDs on the CU: "RDY" green, "BF" off, "LINK" on the PROFINET ports).
3. Run the basic commissioning in Startdrive: set the motor data (p0300…p0335), perform motor identification (p1910), and perform speed controller optimization (p1960).
4. Configure the encoder in p0400 (type), p0404 (configuration), p0408 (pulses per revolution). Verify the encoder is detected correctly using r0458 (encoder diagnostics word).
5. Configure the EPOS function: p2502 = 1, p2506 = 1 (or 2 if encoder 2 is used for position), p2503, p2504, p2580, p2581, p2572, p2573.
6. Configure the PROFINET telegram (111) on the drive in the device view.
7. Load the DriveLib blocks (SINA_POS) into the PLC program and call them with valid parameters. Connect the HWIDSTW and HWIDZSW inputs to the hardware identifiers of the drive's PROFINET telegram in the TIA Portal project.
8. Compile and download the PLC project.
9. Run the drive in jog mode first (mode = 0) to verify the encoder direction. The actual position should increment when the motor rotates in the positive direction. If it decrements, swap p0410 to 1 (direction reversal) or swap the A/B phases on the encoder cable.
10. Set the reference point: trigger "Set reference point" from the PLC (STW1 bit 11), or run active referencing through p2593 (start a homing sequence).
11. Run an MDI motion (mode = 2, absolute) and verify the actual position converges to the target position with zero steady-state error. Monitor the following error on the HMI or in the watch table.

9. Option B — Technology Objects in the S7-1200

9.1 Concept

In Path B, the S7-1200 hosts a positioning axis technology object. The technology object closes the position loop in the PLC. The drive operates in speed-controlled mode (telegram 1 or 3), and the drive's speed setpoint is set by the technology object. This approach is useful when the position loop must interact with other PLC logic (registration marks, master encoder, camming, multi-axis coordination) and the engineering team prefers to keep all motion in the PLC.

9.2 Technology Object Configuration

In the S7-1200 program, add a new technology object:

• "Technology objects → Add new object → Motion Control → TO_PositioningAxis."
• Name: Axis_G120.
• Assign the PROFINET telegram of the drive (telegram 1 or telegram 3).
• Configure the mechanics: load distance per motor revolution, gearbox ratio.
• Configure the encoder source: choose "Encoder on PROFINET IO." The drive's encoder is the source, and the position is read from the drive's status word.
• Configure the limits: maximum velocity, maximum acceleration, maximum jerk.
• Configure the homing procedure: active homing with reference cam and zero pulse, or passive homing through a digital input.

The technology object is connected to the drive through the "Axis" interface in the technology object view. The drive's speed setpoint and enable signals are wired automatically. The MC_Power, MC_MoveAbsolute, MC_MoveRelative, MC_MoveVelocity, MC_Home, and MC_Stop instructions are available as standard PLCopen motion control blocks.

9.3 Encoder Source in Technology Object

For the SINAMICS G120 case, the drive's encoder is the encoder source. The technology object reads the actual position from the drive's process data and computes the speed setpoint, which is sent back to the drive through the same telegram.

9.4 MC_Power and Axis Enable

The MC_Power instruction enables the axis. The Enable input must be TRUE and the drive must be ready (the technology object polls the drive's ZSW1 bit 2 "Operation enabled"). The StopMode input selects the response to a stop request (0 = immediate, 1 = emergency stop with ramp, 2 = emergency stop with jerk-limited ramp).

A typical configuration is:

// MC_Power — enable the axis
MC_Power_inst(
    Axis         := Axis_G120,
    Enable       := bEnableAxis,
    StopMode     := 1,    // 1 = emergency stop with ramp
    Status       => bAxisEnabled,
    Busy         => bAxisBusy,
    Error        => bAxisError,
    ErrorID      => wAxisErrorID
);

10. Homing Procedures

Homing is the procedure that establishes a known position reference for the axis. The SINAMICS G120 EPOS supports several homing modes:

After power-up, the reference point is retained only for absolute encoders (SSI multi-turn, or a multi-turn encoder on the motor). For incremental encoders, the homing sequence must be re-executed on every power-up. The PLC must wait for the "reference point reached" status bit (ZSW1 bit 10) before issuing MDI moves.

11. Process Data and Telegram Mapping (Telegram 111)

In the CU250S-2 with telegram 111, the process data words are mapped as follows. The exact mapping is firmware-dependent and should be verified against the drive's telegram documentation in the operating instructions.

The position setpoint and the actual position are 32-bit signed integers. The scaling is configured in the drive (p2900) and in the technology object (mechanics → load distance per motor revolution). When the two scalings are consistent, the position values are in the same length unit (LU).

12. Reading Encoder Data into PLC Tags

The simplest way to make encoder data visible in a TIA Portal V14 program is to map the drive's actual position to a PLC tag through the SINA_POS block. The block exposes the actual position as a REAL output, which can be assigned to a tag in the PLC's data block.

A minimal example (Path A, EPOS):

1. Add a global DB called DriveData with a REAL tag ActualPosition, a REAL tag ActualVelocity, and a BOOL tag AxisReady.
2. Call SINA_POS in OB1 with the inputs tied to your application logic.
3. Wire the SINA_POS output ActualPosition to DriveData.ActualPosition, ActualVelocity to DriveData.ActualVelocity, and the bit pattern of AxisStatusWord to a AxisReady tag (bit 0 = "ready to switch on", bit 1 = "ready to operate", bit 2 = "operation enabled").
4. Compile, download, and go online.
5. In the watch table or on a HMI screen, observe the value of DriveData.ActualPosition as the motor moves. The value increments and decrements in length units.

A more advanced pattern is to expose the actual position to a HMI (for example, a SIMATIC KTP1200) through a text field with the format %.0f LU, or to an OPC UA server for higher-level monitoring. With TIA Portal V14 and a SIMATIC HMI, the tag is automatically available on the HMI when the HMI connection is configured in the HMI device's "Connections" editor.

13. Verification and Diagnostics

13.1 Online Diagnostics in TIA Portal

13.2 Verifying the Encoder is Connected

1. In the TIA Portal project, open the drive's online view.
2. Navigate to "Diagnostics → Encoder."
3. Read r0458 (encoder actual value). The value should increment when the motor is rotated in the positive direction.
4. If the value does not change, the encoder is not connected correctly. Check the wiring, verify p0400 matches the encoder type, and verify the encoder supply voltage on X9 pin 13 (+24 V) and pin 14 (0 V).
5. If the value changes but in the wrong direction, swap p0410 to 1 (direction reversal) or swap the A and B phases on the cable.
6. Use the control panel to command a small jog motion (in EPOS mode) and verify the actual position follows the setpoint without a following error.

14. Fault Code Reference

The most common encoder- and PROFINET-related faults on the SINAMICS G120 are listed below. The full list is in the G120 with CU250S-2 Control Units operating instructions (PDF, Siemens support, 99730303).

Alarms (Axxxx) are warnings that do not stop the drive; faults (Fxxxx) stop the drive and require acknowledgment (rising edge on STW1 bit 6, or the SINA_POS AcknowledgeFaults input).

15. Troubleshooting Matrix

16. Field-Proven Caveats

Firmware-dependent encoder support. The CU250S-2 firmware version controls which encoder types are supported and what parameters are available. For SSI encoders, firmware V4.5 or higher is recommended. For HTL encoders with cable lengths over 50 m, use a 24 V push-pull driver at the encoder and route the cable away from VFD power cables.

PROFINET update time. The default PROFINET update time is 1 ms. For positioning accuracy in the 0.1 mm range with a 1024 ppr encoder, 1 ms is acceptable. For higher accuracy, increase the update time on the IO controller to 0.5 ms. Note that not all PROFINET IO controllers support 0.5 ms; the S7-1200 supports it on the PROFINET interface of most CPU variants.

Reference point retention. The CU250S-2 retains the reference point across power cycles only for multi-turn absolute encoders. For incremental encoders, the homing sequence must be re-executed on every power-up. The PLC must wait for the "referenced" status bit (ZSW1 bit 10) before issuing MDI moves.

Following error handling. A persistent following error indicates a mechanical issue or a mis-tuned position controller. The drive's p2544 (following error tolerance) and p2546 (following error timeout) are the standard parameters. For a project with a learning curve, set p2544 to a large value (for example, 10000 LU) initially, and tighten it once the motion is working.

Earthing and shielding. Encoder cables must use twisted pairs with an overall shield, and the shield must be bonded to the cabinet ground at the drive end only. Floating shields are a common source of noise-induced encoder faults (F31117, F31136).

TIA Portal V14 compatibility. DriveLib V14 is the correct library for TIA Portal V14. DriveLib V13 SP1 may also be used, but the block interfaces might differ slightly. For TIA Portal V15 and higher, a newer DriveLib is required. Mixing libraries and TIA Portal versions is a common cause of compile errors.

PLC firmware. The S7-1200 AC/DC/RLY used in this project must have firmware V4.2 or higher to support the required DriveLib blocks. Older firmware versions do not support some motion control instructions and will reject the SINA_POS call with a type error.

Encoder cable length. The maximum cable length for HTL encoders on the CU250S-2 is approximately 100 m at 24 V. For TTL encoders, the maximum is approximately 50 m at 1 MHz. For longer cable runs, a signal repeater or a line driver is required.

Two-encoder configuration. When two encoders are connected (one to X9, one to X10), the speed controller uses one encoder (typically the motor-mounted encoder on X9) and the position controller uses the other (the external machine encoder on X10). The assignment is made through p2506 and the speed/position controller encoder selectors. The combination rules are documented in the Encoder combinations for SINAMICS G120 CU250S-2 (PDF, Siemens support, 109813048).

17. Worked Example: From Power-On to First MDI Move

The following sequence summarizes a first-time commissioning of a SINAMICS G120 CU250S-2 PN with a TTL incremental encoder on X9, controlled by an S7-1200 through SINA_POS, on TIA Portal V14.

1. Hardware. Wire the encoder to X9: A+ to pin 1, A− to pin 2, B+ to pin 3, B− to pin 4, +24 V to pin 13, 0 V to pin 14. Bond the shield to the connector backshell. Connect PROFINET port 1 of the CU to the S7-1200 PROFINET port.
2. Project creation. Create a new TIA Portal V14 project. Add the S7-1200 CPU and the G120 CU250S-2 PN. Assign IP addresses (PLC: 192.168.0.10, drive: 192.168.0.20) and PROFINET device names.
3. Telegram. Configure telegram 111 on the drive's PROFINET interface.
4. DriveLib. Install DriveLib V14. Drag SINA_POS into the PLC program. Open the call options and connect the block to the drive's PROFINET telegram. The HWIDSTW and HWIDZSW inputs are populated automatically.
5. Drive parameters. With Startdrive, go online to the drive. Set p0015 to the EPOS macro (typically macro 7, verify against the firmware). Set p0300…p0335 to match the motor. Set p0400 = 2 (TTL), p0408 = 1024 (encoder ppr). Set p2502 = 1 (EPOS enable), p2506 = 1 (encoder 1 for position), p2580 = −1000000, p2581 = 1000000 (software limits in LU).
6. Commissioning. Run p1910 (motor identification) and p1960 (speed controller optimization). Save the parameters to the drive's non-volatile memory (copy RAM to ROM, p0971 = 1).
7. Encoder test. Open the drive's online view in TIA Portal, navigate to "Diagnostics → Encoder." Read r0458. Rotate the motor by hand and verify the value increments. If it decrements, set p0410 = 1.
8. PLC program. In OB1, call SINA_POS with the application logic. Set Mode = 0 (jog) and PositiveDirection = TRUE briefly. Verify the motor rotates in the expected direction. Set Mode = 0 and NegativeDirection = TRUE briefly. Verify the motor rotates in the opposite direction.
9. Homing. Execute active homing through p2593, or set p2596 = 1 from the PLC to set the current position to p2503. Verify ZSW1 bit 10 ("Reference point reached") is TRUE.
10. First MDI move. Set Mode = 2 (MDI absolute), Position = 1000 (LU), Velocity = 1000 (LU/min), Acceleration = 1000 (LU/s²). Pulse ExecuteMode. Verify the motor moves to position 1000 LU and the actual position in the watch table converges to 1000.
11. Error handling. Read the drive's fault buffer (r0947) and alarm buffer (r2110) after any unexpected behavior. Clear faults by pulsing the SINA_POS AcknowledgeFaults input.

18. References to Official Siemens Documentation

G120 with CU250S-2 Control Units operating instructions (PDF, Siemens support, 99730303) — primary commissioning manual for the CU250S-2 Control Unit, including encoder wiring, parameter assignment, and fault diagnosis.

Encoder combinations for SINAMICS G120 CU250S-2 (PDF, Siemens support, 109813048) — application note describing the supported encoder combinations and the assignment of two encoders to speed/position control.