SINAMICS S110 CU305 CAN: RS232 X22 Connection to STARTER

Overview

The SINAMICS S110 Control Unit CU305 CAN (MLFB 6SL3040-0JA02-0AA0) is the CAN-bus variant of the modular single-axis servo drive controller in the SINAMICS S110 family. The unit is identified by the Machine-Readable Product Code on the front-panel nameplate, by the firmware version reported in parameter r0018, and by the three status LEDs (RDY, COM, OPT) on the front cover. The CU305 CAN is typically paired with a SINAMICS PM340 (Blocksize format) power module in the 1AC 230 V, 3AC 400 V, or 3AC 480 V class.

Three practical paths exist for connecting a PG/PC to the CU305 CAN for commissioning:

1. X22 service interface (RS232 / point-to-point / USS) — universal across all CU305 variants, requires only a null-modem cable.
2. X126 (CAN bus, CANopen protocol) — requires a USB-to-CAN adapter such as PEAK PCAN-USB or Vector VN1610.
3. PROFIBUS / PROFINET — not native to the CAN variant. Use a CU305 DP (6SL3040-0JA01-0AA0) or CU305 PN (6SL3040-0JA00-0AA0) variant instead.

This article covers the X22 RS232 service interface path in depth, including cable wiring, USB-to-serial adapter selection, STARTER configuration, and the commissioning workflow. The X126 CANopen path and the safety / STO wiring are covered as secondary topics because they are commonly requested in the same commissioning session.

The authoritative reference for the S110 platform is the SINAMICS S110 Equipment Manual and the product support page at Siemens Industry Online Support for 6SL3040-0JA02-0AA0. Always verify the chapter for your specific firmware version — the pinout and parameter set are stable, but parameter ranges and default values evolve across firmware versions.

Hardware Identification

Confirm the MLFB on the nameplate before connecting. The DP and PN variants look identical from the front but have different firmware images and fieldbus connectors.

Prerequisites

• PG/PC with Windows 7 SP1 / Windows 10 (32-bit or 64-bit), at least one free USB port, or a built-in RS232 COM port.
• STARTER commissioning tool, version V4.5 SP1 or later (V5.5 HF1 is the last version to officially support the S110 device family for legacy reasons). The S110 device description is bundled in STARTER from V4.4 onwards.
• Alternative: Startdrive in TIA Portal V13 SP1 / V14 / V15.1 / V16 / V17. Startdrive replaces STARTER for new installations.
• Null-modem (crossover) RS232 cable, 9-pin D-sub female to 9-pin D-sub female, with TxD and RxD crossed.
• If the PC has no DB9 COM port, a USB-to-RS232 adapter based on a proven chipset (FTDI FT232R or Silicon Labs CP2102N).
• 24 V DC supply at the CU305 X124 terminal (the CU305 is not powered from the PM340 DC link alone — the control electronics require an external 24 V).
• STARTER license. A 14-day trial license can be activated through License Manager → Trial License → Activate Online.

X22 RS232 Service Interface — Pinout

The X22 connector is a 9-pin D-sub male (with pins) on the CU305 front cover. It is wired as a DTE (Data Terminal Equipment) port — the same orientation as a PC COM port. The pin assignment per the SINAMICS S110 Equipment Manual is:

Standard RS232 levels (±3 to ±15 V) are used. Hardware flow-control lines (RTS / CTS) are not implemented on the CU305; a 3-wire null-modem cable is therefore sufficient and is the recommended wiring.

Null Modem Cable Specification

Two DTE devices (the PG/PC and the CU305) cannot be connected with a straight-through cable. A null-modem crossover is required. The minimum wiring is:

Standard commercial null-modem cables (DB9 F/F) are available from any industrial supplier. Recommended part numbers:

• StarTech SCNM9FM (3 m, DB9 F/F, foil-shielded)
• L-com CSF9MF-3 (3 m)
• Siemens 6XV1 840-2AH10 (5 m, factory-prefabricated, recommended for cabinet applications)

Maximum cable length: 15 m at 19 200 bps; 3 m at 115 200 bps. For S110 commissioning at the default baud rate (19 200), 3–5 m is the practical working distance and gives the best noise margin.

USB-to-RS232 Adapter Selection

Modern PCs and laptops no longer ship with a DB9 COM port. A USB-to-RS232 adapter is required. The adapter chipset directly affects RS232 link stability with Siemens drives; cheap Prolific PL2303 clones (HXA, HXD, TA, RA re-marked chips) are known to corrupt frames at higher baud rates and to lose sync during long parameter downloads.

Adapters to avoid:

• Prolific PL2303 HXA / TA re-marked clone chipsets (Windows 10 may refuse to install drivers).
• WCH CH340 — works at 19 200 bps but is sensitive to ESD and to USB hub transient noise.

Set the assigned COM port to a fixed low number (COM1–COM4) via Windows Device Manager → Port Properties → Advanced → COM Port Number. COM port numbers above 10 occasionally require a registry edit (HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Siemens\Automation\S7WSI\ComUserPort) in older STARTER builds.

Default RS232 Communication Parameters

After a factory reset of the CU305 (p0970 = 1 or p0972 = 1), the X22 service interface operates with the following default values:

Match the COM port settings exactly in STARTER: 19 200 / 8 / N / 1 / no flow control. The drive does not autobaud on X22. If the baud rate is changed in STARTER (parameter p2010 / p2011 in the drive), the new value is only active after a CU305 restart (power off / on, or p0972 = 1 with the standard wait time of 30–60 s).

STARTER vs Startdrive — Tool Selection

Use STARTER when you have an existing S110 project archive, when you need full trace / function generator functionality, or when the drive firmware is below V5.1. Use Startdrive for new TIA Portal installations, for S7-1200 / S7-1500 PLC integration, and for firmware V5.x and above.

Step-by-Step: Connect CU305 to STARTER via X22

1. Bond PE. Connect the cabinet PE to the M6 PE stud on the CU305 front cover using a 10–50 mm² ring cable lug. The M8 PE stud on the PM340 power module takes a max 120 mm² ring cable lug. Reference: SINAMICS S110 Equipment Manual, "PE connection" section.
2. Power the drive. Apply 24 V DC to the X124 terminal on the CU305. Switch on the line voltage (or precharge the PM340 DC link if a Line Module is upstream). The RDY LED will go red, then flash green, then steady green when the unit is ready (typically 5–10 s after power-up). A steady red RDY indicates a fault — read r0947 / r0948 before continuing.
3. Plug the null-modem cable into X22 on the CU305 and the COM port (or USB-to-RS232 adapter) on the PG/PC. Hand-tighten the thumbscrews on both DB9 connectors.
4. Verify the COM port number in Windows Device Manager → Ports (COM & LPT). Note the assigned COM number (e.g., COM3). If the COM number is above 10, change it to COM1–COM4 in the adapter advanced properties.
5. Launch STARTER. Project → New → assign a project name and storage path. In the project navigator, right-click Drive unit → Insert new object → SINAMICS S110. In the device selection dialog, choose CU305 CAN (type designation shown as "SINAMICS S110 CU305 CAN").
6. Configure the PG/PC interface. In STARTER, select Options → Set PG/PC interface. The access point is S7ONLINE (STEP7) → PC serial (RS232, PPI) for the X22 path. Choose the assigned COM port and click OK.
7. Go online. Right-click the S110 drive object → Connect to target system. STARTER will compare the offline project to the drive firmware. On the first connection, choose Upload from target (load to PG) to read the actual drive parameters into the project. After subsequent firmware or topology changes, choose Download to target to write the offline configuration to the drive.
8. Verify the connection. The COM LED on the CU305 should pulse green every time STARTER polls. The status bar at the bottom of STARTER turns green and the active faults / alarms list refreshes. The online version of r0018 (firmware version) should match the version in the offline project.
9. Commission the drive. Run the STARTER commissioning wizard. Set p0010 = 1 (quick commissioning) and step through:
   • Motor type: 1FK7 / 1FT7 / 1PH8 (Siemens motor) or third-party induction / synchronous motor.
   • Encoder type: resolver, EnDat 2.1, sin/cos, TTL, HTL — wired via SMC / SME Sensor Module on the DRIVE-CLiQ chain.
   • Control mode: servo (for 1FK / 1FT / 1PH synchronous), vector (for 1PH / 1LA induction), or V/f (for simple induction motors).
   • Current, speed, and torque limits per the motor nameplate.
10. Save and back up. Set p0010 = 0. Set p0971 = 1 to save parameters to non-volatile memory (RAM → ROM). Right-click the drive → Load to file system to save the project archive. Optionally insert a Siemens memory card in slot X1 and set p0977 = 1 to copy the parameter set to the card for field-replacement backup.

Verification After Online Connection

Before enabling any motion, perform these checks:

• STARTER status bar is green and the drive shows as Online.
• r0018 (firmware version) matches the project version. Mismatch = STARTER may not display all parameters correctly.
• r0020 / r0021 (control / status word 1) — the drive should report Ready to switch on (status word bit pattern 0x...31 in binary) once the enable chain is closed.
• r0947 (fault code) = 0 and r2122 (alarm code) = 0. Any non-zero value must be cleared before motion commissioning.
• p0010 = 0 (drive returns to "Ready" state) before any motion enable.
• r3996 (LED status word) — bit 0 = RDY state, bit 1 = COM state. Used for cross-checking the front-panel LEDs.

Memory Card Backup Procedure

After commissioning, back the parameters up to the CU305 MMC / SD card slot (X1, behind the front cover):

1. Insert a Siemens-approved memory card: 6SL3054-0AA01-1AA0 (8 MB) for S110 firmware V4.x, or 6SL3054-0AG01-1AA0 (512 MB) for V5.x. Third-party SD cards work but are not guaranteed to be compatible with the CU305 bootloader.
2. Set p0977 = 1 (RAM → ROM → memory card). Wait for the CU305 to perform the copy cycle (5–30 s, depending on card size).
3. Verify the copy by reading parameter p9400 / p9401 (card parameter set version) or by removing the card, mounting it in a card reader, and confirming the presence of the SAVE directory and userdata.bin file.

A card with a valid parameter set can be hot-swapped to a replacement CU305 to bring the new Control Unit to the same state as the old one, without needing a PG/PC connection.

Alternative: CANopen via X126

For installations where the CU305 is already wired to a CANopen bus, the X126 port can be used for STARTER commissioning without disturbing the field wiring. Required hardware and settings:

• USB-to-CAN adapter: PEAK-System PCAN-USB (IPEH-002021), Vector VN1610, or HMS Ixxat USB-to-CAN V2.
• STARTER V4.5 SP1 or later (Startdrive in TIA Portal V14 or later) with the CAN device description installed.
• CAN baud rate (default 1 Mbit/s, settable to 10, 20, 50, 100, 125, 250, 500, 800, 1000 kbit/s via p8620).
• CAN node ID (default 1, settable 1–127 via p8621 or the CU305 front-panel DIP switch).
• 120 Ω bus termination at both physical ends of the CAN bus (the CU305 CAN variant does not include an internal termination resistor — install it at the connector if the CU305 is at the end of the segment).

Set the STARTER PG/PC interface to PC internal/PC local → PCAN-USB (or your specific adapter). The connection procedure after this point is identical to the X22 path.

PROFIBUS / PROFINET — Variant Note

The CAN variant of the CU305 (6SL3040-0JA02-0AA0) does not include a PROFIBUS or PROFINET interface. If PROFIBUS-based STARTER commissioning is required, use the CU305 DP variant (6SL3040-0JA01-0AA0). For PROFINET, use the CU305 PN variant (6SL3040-0JA00-0AA0). Do not attempt to connect PROFIBUS or PROFINET cables to X126 — X126 is the CAN bus and the physical-layer voltage levels are incompatible (CAN uses differential 2.7 V / 1.3 V on CAN_H / CAN_L, PROFIBUS uses RS485 ±1 V differential).

LED Status Reference

Fault and Alarm Code Reference

Always read r0947 for the most recent fault, r0948 for the fault time stamp (in 24-hour format from the CU305 real-time clock, which is buffered by the 24 V supply), and r0949 for the fault value.

Troubleshooting Matrix

EMC and Shielding Best Practice

For a reliable RS232 commissioning link in an industrial cabinet:

• Use a shielded cable and connect the shield to cabinet ground only at the drive end to avoid ground loops. If the drive is more than 5 m from the PG/PC, use a separate PE run between the PG chassis and the cabinet PE.
• Keep the RS232 cable at least 200 mm from any 400 V power wiring, and never run it in the same cable tray as motor power leads.
• Do not route the cable parallel to motor power leads for more than 1 m; cross at 90° if crossing is required.
• The CU305 PE stud (M6) must be bonded to cabinet PE with a ring lug sized for the installation (10–50 mm² per the SINAMICS S110 Equipment Manual). The PM340 PE stud (M8) accepts a max 120 mm² ring lug.
• If the drive is fed by an ungrounded IT line supply, install a residual-current monitoring device (RCM) upstream, and use a 4-pole contactor so that all phases are isolated on stop.

Watch Tables and Trace — First Diagnostics

Once online, two STARTER tools are used for 90% of first-day diagnostics:

• Watch table (right-click the drive → Watch table): a tabular view of any parameter (read-only or read/write) that updates in real time. Add r0020, r0021, r0026, r0027, r0031, r0032, r0080, r0082 for a real-time motion / current view. Save the watch table to the project so it loads automatically on next connection.
• Trace (Drive → Trace): time-sampled recording of up to 8 parameters at sample times from 1 ms to 60 s. The trace is downloaded to the drive, runs on the drive firmware (not on the PG/PC, so it is robust against PC timing jitter), and the result is uploaded back to STARTER for graph display. Use the trace to capture step responses, current spikes, and encoder noise.

For S110 firmware V4.x and V5.x, the trace buffer is limited to 2 048 samples per channel. For longer captures, reduce the sample time or use the function generator in STARTER to drive a periodic test signal.

Firmware Update Procedure (Reference)

Firmware updates for the CU305 are performed via STARTER ("Drive → Load firmware to drive") or via a memory card containing the new firmware. Always read the release notes for the new firmware version on the Siemens product support page linked above before updating — some firmware versions require a specific upgrade path (e.g., V4.4 SP3 → V4.5 SP1 → V5.1 SP1) and may not be downgradeable without a service request.

1. Back up the current parameter set to a memory card (p0977 = 1) and to a project archive (right-click → Load to file system).
2. Set p0010 = 0 to ensure the drive is in "Ready" state, not commissioning.
3. In STARTER, right-click the drive → Load firmware to drive. Select the firmware file (*.upd) matching the MLFB and current firmware version.
4. Confirm the version change. The CU305 will restart automatically after the load. Do not power off during the update — the RDY LED will fast-flash green and red for 30 s to 5 min, depending on the firmware size.
5. After the restart, go online, verify r0018 matches the new firmware, and reload the project (Upload from target).

Integration with S7 PLCs (Quick Reference)

For PLC → drive integration, the CU305 CAN is connected to the PLC via CANopen. The S7-300 / S7-400 require a CP 340 or CP 341 module, and the S7-1200 / S7-1500 require a CM CAN module. Drive-side, the following parameter ranges are used for the CANopen profile (DSP 402 / CiA 402):

Refer to the SINAMICS S110 Equipment Manual, "CANopen communication" chapter, for the full parameter list and EDS file integration.

Field Replacement of a Failed CU305

1. Power down the drive (24 V removed, line contactor off, DC link discharged — wait at least 5 min after power-off before touching terminals).
2. Remove all connectors from the failed CU305: X22, X126, X100/X101 encoder, X124 24 V, DRIVE-CLiQ, motor cable, memory card (if present).
3. Insert the memory card from the failed unit into the new CU305 of the same MLFB.
4. Apply 24 V DC. The new CU305 will detect the memory card and load the parameter set from userdata.bin within 30 s. The RDY LED will go steady green when loaded successfully.
5. Reconnect all cabling in the original order.
6. Go online with STARTER. Verify r0018 firmware version matches the memory card version. Verify r0947 = 0 (no faults) and r0021 = 0x...31 (Ready to switch on).

If the memory card is corrupted or missing, the new CU305 will boot with factory defaults. Re-commission via the STARTER wizard as described in the step-by-step section above.

Frequently Asked Questions