1. Overview
The SINAMICS G120 is a modular low-voltage drive family from Siemens. The CU250S-2 DP (Control Unit) is the PROFIBUS-DP variant and supports Vector Control, sensorless position approximation, and—under extended license—Basic Positioner (EPOS). It is intended for induction motors (asynchronous) and for sensorless operation of permanent-magnet synchronous motors (PMSM/servo), but is not a replacement for a high-dynamics servo system such as SINAMICS S120.
This reference consolidates the three recurring engineering questions for the CU250S-2 DP:
- Can a servo (PMSM) motor be used, and what control mode is supported?
- What is the maximum PZD (process data) word count and how is it mapped?
- How do the BICO qualifiers (BI, BO, CI, CO, CO/BO) and the r54 status word interact with PROFIdrive?
2. Hardware Identification and Variants
| Feature | CU250S-2 DP | CU250S-2 PN | CU240E-2 DP |
|---|---|---|---|
| MLFB | 6SL3246-0BA22-1PA0 | 6SL3246-0BA22-1FA0 | 6SL3244-0BA22-1PA0 |
| Fieldbus | PROFIBUS DP | PROFINET / EtherNet/IP | PROFIBUS DP |
| Control modes | V/f, SLVC, Vector with encoder, EPOS* | Same | V/f, SLVC only |
| EPOS (Basic Positioner) | License required | License required | Not supported |
| Configurable DOs | 4 | 4 | 2 |
| Encoder interface | HTL/TTL (onboard) | HTL/TTL (onboard) | None |
* EPOS = Easy Positioning. Activated via license key on the SD card slot of the Control Unit. Without the license, position-mode telegrams (e.g., telegram 110) operate as speed setpoints.
Source: SINAMICS CU250S-2 DP product page (Siemens SiePortal).
3. Servo Motor Compatibility — What the CU250S-2 DP Will and Will Not Do
3.1 Synchronous (PMSM) Motor Operation
Yes, the CU250S-2 DP can be parameterized for a permanent-magnet synchronous motor. The firmware supports the following motor types when paired with the appropriate Power Module (PM240-2, PM250, PM260):
- Induction motor (asynchronous, ASM) — full feature set.
- Permanent-magnet synchronous motor (PMSM) — supported, with the restrictions below.
- Reluctance motor (SyRM) — supported on firmware ≥ V5.1 with auto-tuning.
3.2 Sensorless Vector Control (SLVC) Limitation
The defining limitation: PMSM control on the CU250S-2 DP is sensorless only when the positioner is not licensed. The drive estimates rotor angle from the EMF/back-EMF model. This imposes hard practical limits:
| Limit | Value / Behavior |
|---|---|
| Lowest stable operating speed (typical) | ≈ 5–10 % of rated speed with load; ≈ 2 % at no load |
| Zero-speed holding torque | Not guaranteed — rotor may unlock and step |
| Position accuracy (sensorless, EPOS) | ± 0.5 ° to ± 5 ° electrical, load-dependent |
| Reversal transients | 0.5–2 s settling, can produce audible cogging pulses |
| Auto-tuning requirement | Mandatory (p1910 / p1960) for PMSM; skip leads to F07900 |
3.3 PMSM Commissioning Checklist
- Set p0300 = 2 (PMSM) and enter motor nameplate into p0301, p0304, p0305, p0307, p0308, p0310, p0311.
- Enter p0314 (motor pole pair number). Verify:
p0314 = round(60 * p0310 / p0311). - Set p1300 = 20 (sensorless vector control) for sensorless operation, or 21 (vector control with encoder) if an HTL/TTL encoder is wired.
- Run stationary measurement p1910 = 1, then rotating measurement p1960 = 1, both with the motor decoupled from the load.
- For EPOS, install license and select telegram 110 (4 PZD) or telegram 111 (12 PZD).
4. BICO Parameter System
The BICO system (Binector/Connector) is the signal-routing engine inside SINAMICS. Every parameter that can be interconnected carries a prefix qualifier. The five you will see in the parameter list of a G120 are summarized below; CU250S-2 follows the same definitions as the wider SINAMICS platform.
| Prefix | Name | Signal Type | Direction | Typical Use |
|---|---|---|---|---|
| BI | Binector Input | Digital (1 bit) | Sink (selects source) | Assign a digital signal to a function: e.g., p0840[0] BI: ON/OFF1
|
| BO | Binector Output | Digital (1 bit) | Source (drives consumers) | Source for any BI; e.g., r0052 BO: Status word 1 bit 0
|
| CI | Connector Input | Analog (16/32 bit) | Sink (selects source) | Assign a numeric setpoint: e.g., p1155 CI: Speed setpoint 1
|
| CO | Connector Output | Analog (16/32 bit) | Source | Numeric actual value: e.g., r0021 CO: Actual speed smoothed [rpm]
|
| CO/BO | Connector/Binector Output | Combined (32-bit word containing 32 digital bits) | Source | Status/control words that can be read as a number or bit-indexed: e.g., r0052 CO/BO: Status word 1
|
4.1 CO/BO vs BO — the practical difference
Both BO and CO/BO expose digital bits. The distinction is memory layout:
-
BO = exactly 1 bit. Always addressable as
rXXXX.B00. It is the digital atom of BICO. -
CO/BO = a 32-bit word whose individual bits are aliased as
rXXXX.B00throughrXXXX.B15(or .B31). You can read the entire 16-/32-bit word in one PROFIdrive PZD or re-route individual bits to other BIs.
Therefore r0054 (CU250S-2 control word 1, ZSW1) being displayed as CO/BO means: you can read it as a 16-bit word on PROFIBUS and you can pick individual bits to feed other BIs inside the drive. That is the bridge between PZD and the BICO world.
5. PROFIdrive Communication Profile and PZD Length
On PROFIBUS DP, the CU250S-2 DP is a PROFIdrive Class 1 (single-axis) drive. The drive exchanges process data (PZD = Prozessdaten) cyclically with the PLC:
- PZD receive (PLC → drive): control word (STW1) and setpoints.
- PZD send (drive → PLC): status word (ZSW1) and actual values.
5.1 Maximum PZD Count
The CU250S-2 supports up to 14 PZD words in each direction (per the fieldbus manual, Siemens ID 109482981). With 16 bits per PZD, that is 28 bytes cyclic payload per direction. In practice, you should use the smallest standard telegram that meets your needs and pad the rest with vendor-specific words only if required.
5.2 Standard PROFIdrive Telegrams for CU250S-2
| Telegram (p0922) | PZD Count | Direction Layout (PLC ↔ Drive) |
|---|---|---|
| 1 (default) | 2 / 2 | STW1 / ZSW1 + NSOLL / NIST |
| 2 | 4 / 4 | + NSOLL_B / NIST_B (32-bit setpoint/actual) |
| 3 | 2 / 3 | STW1 / ZSW1 + 1 setpoint / 2 actuals (NIST + IAIST) |
| 4 | 6 / 6 | STW1/STW2 / ZSW1/ZSW2 + extended set/actual |
| 5 | 6 / 10 | STW1/STW2 / ZSW1/ZSW2 + full setpoint / full actual (for 2 encoders) |
| 7 | 2 / 2 | STW1 / ZSW1 + simple positioning (with EPOS license) |
| 9 | 2 / 2 | STW1 / ZSW1 + NSOLL/NIST + MELD_NAMUR (NAMUR status word) |
| 20 | 2 / 6 | STW1 / ZSW1 + setpoints / actuals (SIEMENS-specific) |
| 110 | 4 / 4 | STW1/STW2_POS / ZSW1/ZSW2_POS + EPOS set/actual (with EPOS license) |
| 111 | 12 / 12 | STW1/STW2_POS / ZSW1/ZSW2_POS + EPOS full set/actual (with EPOS license) |
| 999 (free) | 0–14 / 0–14 | User-defined via p2051/p2061, p2080/p2081 |
5.3 Verifying the User's PZD1 / PZD2 Assumption
The user's premise is correct for standard telegram 1 (the default):
- PZD1 (PLC → drive): Control word 1, p2050[0] = r0050 (STW1, CO/BO).
- PZD1 (drive → PLC): Status word 1, p2051[0] = r0052 (ZSW1, CO/BO).
- PZD2 (PLC → drive): Speed setpoint, p2050[1] = r0062 (CO: speed setpoint pre-ramp, [rpm] × 1).
- PZD2 (drive → PLC): Actual speed, p2051[1] = r0021 (CO: actual speed smoothed, [rpm] × 1).
If you switch to telegram 2, PZD2 becomes a 32-bit speed setpoint/actual (NSOLL_B / NIST_B), and the next two words (PZD3, PZD4) carry the lower 16 bits. The hex frame to a SIMATIC PLC therefore grows from 4 bytes to 8 bytes per direction.
6. r0054 — Status Word 1 Bit-by-Bit
The user's reference to r54 Bit0 … Bit15 corresponds to r0054, which on CU250S-2 DP is labeled ZSW1 (Status Word 1) and qualified as CO/BO. Bit access syntax: r0054.B00 through r0054.B15.
Bits marked with a black quarter (■) in the parameter list are the bits that are automatically wired into the PROFIdrive profile when the drive is in a cyclic PROFIBUS exchange — they appear directly in the PZD without user interconnection. The remaining bits still exist in r0054 but require BICO routing to be re-routed to other BIs.
| Bit | Mnemonic (PROFIdrive) | Meaning (ZSW1) | Auto-mapped to PZD |
|---|---|---|---|
| 0 | RDY_ON | Ready to switch on | Yes (■) |
| 1 | RDY_RUN | Ready to operate (DC link charged, no faults) | Yes (■) |
| 2 | RDY_REF | Operation enabled (drive following setpoint) | Yes (■) |
| 3 | FAULT | Fault active | Yes (■) |
| 4 | NO_OFF2 | No coast stop active (OFF2 absent) | Yes (■) |
| 5 | NO_OFF3 | No quick stop active (OFF3 absent) | Yes (■) |
| 6 | INHIBIT_ON | Switch-on inhibited (acknowledge needed) | Yes (■) |
| 7 | ALARM | Alarm active (non-fatal) | Yes (■) |
| 8 | AT_SETPOINT | Speed deviation within tolerance (p2161) | Yes (■) |
| 9 | REMOTE | Control requested from PLC (parallel interface mastered) | Yes (■) |
| 10 | F_N_REACHED | Speed setpoint reached or exceeded | Yes (■) |
| 11 | I_M_P_LIM | Current / torque / power limit reached | Yes (■) |
| 12 | BRAKE_OPEN | Holding brake released (when configured) | Yes (■) |
| 13 | NO_OVOLT_WARN | No motor over-temperature warning | Yes (■) |
| 14 | FWD_RUN | Motor rotates forward (n_act ≥ 0) | Yes (■) |
| 15 | NO_OTMP_WARN | No power unit over-temperature warning | Yes (■) |
On the CU250S-2 with a normal PROFIdrive telegram, all 16 bits of r0054 are auto-mapped — that is why the user sees a complete status word on the PLC side without configuring any p2051 entries. Manual wiring is only required if you switch to a free telegram (p0922 = 999) and need to restore the status word manually.
7. Free Telegram Configuration (p0922 = 999)
If you set p0922 = 999, you take responsibility for wiring the cyclic data. The two key parameter groups are:
| Parameter | Function | Index convention |
|---|---|---|
| p2051[0..13] | PZD send (drive → PLC) word sources | Index = PZD offset 0–13 |
| p2061[0..13] | DSx (drive-to-drive or peer) source words | For peer-to-peer, optional |
| p2080[0..15] | BI multiplexer → word concatenation for sending | Used to pack individual BOs into a custom word |
| p2081[0..15] | BI multiplexer inversions (negate bit) | Bit-level inversion before p2080 |
| p2099 | CI source for a connector to be included in p2080 word | Analog bits |
7.1 Worked Example — Replicating Telegram 1 Manually
- Set p0922 = 999 (free telegram).
- Set p2079 = 4 (4 PZD per direction = 2 receive + 2 send).
- Set p2051[0] = r0052 (ZSW1, CO/BO → PZD1 send).
- Set p2051[1] = r0021 (actual speed, CO → PZD2 send).
- Set p2060[0] = 1001 (PZD1 receive default = control word 1 source).
- Set p2060[1] = 1002 (PZD2 receive default = speed setpoint source).
Note: the receive path is normally handled automatically by the PROFIdrive stack; p2050 is a display parameter (r2050) on most SINAMICS drives for receive, while p2060[ ] is the signal sink routing. In SINAMICS V5.x firmware, p2050 is read-only and p2061/p2063 represent the send-side sinks. Refer to the CU250S-2 Control Units manual for the exact firmware version-specific mapping.
8. Direction-of-Operation State Diagram (ZSW1 / STW1)
The standard PROFIdrive state machine is replicated inside the CU250S-2 DP. The four core states (S1 Not ready, S2 Ready to switch on, S3 Ready to operate, S4 Operation enabled) are reflected in ZSW1 bits 0–2. Transitions are driven by STW1 bits 0 (OFF1), 1 (OFF2), 2 (OFF3), 3 (Enable), 7 (Acknowledge).
9. Quick Parameter Reference Card
| Parameter | Name | Default / Range | Notes |
|---|---|---|---|
| p0010 | Drive commissioning parameter filter | 0 (Ready) / 1 (Quick) / 30 (Restore factory) | Set to 1 to enter quick commissioning |
| p0015 | Macro drive unit | 0 (no macro) – 31 | Select a factory macro for I/O + telegram |
| p0100 | Motor standard | 0 (IEC/kW) / 1 (NEMA/hp) | Sets p0304 / p0305 units |
| p0300 | Motor type | 1 = IM, 2 = PMSM, 6 = SyRM | PMSM requires p1910 + p1960 |
| p0301 | Motor code (from nameplate list) | 0 (manual entry) | 1xxxx typical for Siemens 1FK/1FT/1PH |
| p1300 | Open-loop/closed-loop control mode | 0 = V/f, 20 = SLVC, 21 = VC+encoder | 21 requires HTL/TTL encoder wired to X9 |
| p0922 | PROFIdrive telegram selection | 1 (default), 2, 3, 4, 5, 7, 9, 20, 110, 111, 999 | 110/111 require EPOS license |
| p2051[0..13] | PZD send word n source | Default telegrams auto-fill | Edit only if p0922 = 999 |
| p2080[0..15] | BI → PZD bit packer | 0 | Pack 16 BOs into a custom word |
| p2099 | CI source of connector for p2080 | 0 | One analog word via BICO bits |
| r0020 | CO: Speed setpoint before RFG [rpm] | — | Signed integer |
| r0021 | CO: Actual speed smoothed [rpm] | — | Default PZD2 send |
| r0050 | CO/BO: Control word 1 (STW1) | — | Mirror of last received STW1 |
| r0052 | CO/BO: Status word 1 (ZSW1) | — | Auto-mapped to PZD1 send |
| r0054 | CO/BO: Status word 1 alternate (CU250S specific mapping) | — | Same bit semantics as r0052 on this firmware |
On firmware ≥ V5.1, parameter r0054 is the CU250S-2-specific status word. The user’s reference to r54 → r0054 is therefore correct and can be used as the PROFIdrive status word 1 source if you wire p2051[0] = 0054.
10. Verification Procedure After Configuration
- Connect the SINAMICS G120 to the PROFINET/PROFIBUS master (S7-1200, S7-1500, ET200S IM151, or any PROFIdrive Class 1 master). Download the GSD file
SIEM8190.gsd(or newer) into the PLC hardware catalog. - Slot the CU250S-2 into the Power Module. Power on, run
p0010 = 1, p3900 = 1to perform quick commissioning (or use STARTER / Startdrive). - Configure GSD slot 1 to the desired telegram (default 1). Map the drive's PIW/PQW to PLC tags.
- Set
STW1 = 0x047E(decimal 1150) in the control word to enter Run state 1 (Ready to switch on). ThenSTW1 = 0x047F(decimal 1151) to enable operation. - Apply a small speed setpoint (e.g., 100 rpm) and verify ZSW1 returns 0x06B7 (decimal 1719) = bits 0,1,2,4,5,6,7,8,9,10 set (Ready, Operation enabled, Inhibit cleared, At setpoint).
- Stop the drive by clearing bit 0 (OFF1) — never by just removing the setpoint; the drive will interpret setpoint = 0 as a valid 0-rpm command, not a stop.
0x0000 as OFF1 — that drops the drive into Coast stop if OFF2 (bit 1) is also 0. The correct OFF1-only sequence is 0x047E → 0x047E (keep all other bits, clear bit 0) or use the OFF1 ramp-down via 0x043E.11. Common Commissioning Faults
| Fault Code | Name | Likely Cause on CU250S-2 DP | Remedy |
|---|---|---|---|
| F07801 | Motor overcurrent | PMSM started in SLVC without p1960; or p0305 wrong | Re-run p1960; verify motor nameplate |
| F07900 | Motor blocked | SLVC with PMSM stalls at low speed under load | Reduce load, raise p1610, switch to VVC+encoder |
| F08501 | PROFIBUS failure | Loss of cyclic PZD; watchdog expired | Check connector, bus terminator, p2040 watchdog time |
| F30002 | DC link overvoltage | Regenerative ramp too fast; missing brake chopper | Extend ramp-down, fit brake resistor, enable p1230 |
| F01910 | p1910 measurement failure | Motor not decoupled, no current flow | Decouple motor, check p0300, p0304, p0305 values |
12. FAQ
Can I use a Siemens 1FK7 / 1FT6 servo motor with a SINAMICS G120 CU250S-2 DP for closed-loop position control?
Only as a sensorless setup. The CU250S-2 DP supports PMSM motors in SLVC (p1300 = 20) and with the EPOS license can command positions, but with no encoder feedback the position accuracy is typically ±0.5° to ±5° electrical. For tight servo position control, use SINAMICS S120 with CU310-2 or CU320-2 and an SMC30 encoder module.
How many PZD words does the CU250S-2 DP support on PROFIBUS?
Up to 14 PZD in each direction (28 bytes cyclic payload), per the fieldbus manual (Siemens ID 109482981). In practice select the smallest standard telegram that meets your need: telegram 1 (2/2), telegram 2 (4/4), telegram 110 (4/4) for EPOS, or telegram 111 (12/12) for full EPOS with all actual values.
What is the difference between BO and CO/BO on a SINAMICS parameter?
BO is a single digital bit (1 bit). CO/BO is a 32-bit word whose individual bits are exposed as rXXXX.B00 through rXXXX.B15. A CO/BO can be read as a complete word in a PZD (e.g., ZSW1 in p2051) or its individual bits can be wired to other BIs. The status word r0054 is a CO/BO on the CU250S-2.
Do I need to manually wire r0054 bits to PROFIBUS to get the status word?
No. With a standard PROFIdrive telegram (1, 2, 3, 4, 5, 7, 9, 20, 110, 111) the drive automatically maps all 16 bits of ZSW1 (r0052 / r0054) into PZD1 send. Manual wiring through p2051 and p2080 is only needed if you select the free telegram p0922 = 999.
Where can I download the official CU250S-2 manual and GSD file?
The CU250S-2 Control Units manual is at Siemens Support (PDF, G120_CU250S2_KBA1_0414_eng_en-US.pdf). The PROFIdrive communication manual is at Siemens ID 109482981. The product page for the CU250S-2 DP is 6SL3246-0BA22-1PA0. The parameter list (List Manual) is in Siemens ID 77498613.