SINAMICS G120 CU230P-2 USB Driver: Install Without Power Module

Problem Overview

Engineers commissioning a SINAMICS G120 drive equipped with a CU230P-2 Control Unit (CU230P-2 HVAC, CU230P-2 DP, CU230P-2 PN, or CU230P-2 BT) frequently report that the USB commissioning cable fails to enumerate on the PC even though STARTER (or Startdrive) is already installed. Windows Device Manager typically displays the generic SINAMICS G120 device family driver, but no virtual COM port appears, and STARTER cannot establish an online connection to the Control Unit.

The problem is most acute when the Control Unit is on the engineer's desk while the Power Module remains bolted into the customer cabinet. A pre-delivery bench test must therefore be run from a CU that is physically separated from its PM. Adding to the confusion, the SINAMICS G120 Operating Instructions state that the USB driver is supplied on the installation DVD shipped with the drive, which most field engineers never receive when a CU is ordered as a spare or replacement part. This article documents the field-proven procedure to install the missing USB-serial adapter driver, assign the correct PG/PC interface, and bring a CU230P-2 online without ever connecting a Power Module.

Hardware Identification and Variants

Before troubleshooting, confirm the exact Control Unit variant. The CU230P-2 family shares firmware architecture and USB behavior, but fieldbus interfaces differ and influence which commissioning parameters you can edit offline.

The CU250S-2 variants (also part of the G120 family) share the same USB stack and use the identical driver set described below; the procedure is interchangeable.

Prerequisites

Before starting, verify the following:

• Commissioning software: STARTER V4.1.5 or higher (V5.x recommended for current firmware), or Startdrive V15 or higher in TIA Portal. STARTER can still be downloaded as the legacy commissioning tool from the Siemens Industry Online Support entry at STARTER commissioning tool (entry ID 10804985).
• Operating system: Windows 7 SP1, Windows 10 (1809 or later recommended), or Windows 11. Windows 8/8.1 also works but signed-driver behavior changed significantly with Windows 10 1607.
• USB cable: Standard USB 2.0 A-to-Mini-B cable, 3 m or shorter. Active cables or hubs may prevent enumeration.
• 24 V supply for the CU: External 24 V DC (0.5 A minimum, 1 A recommended) wired to terminals 1 (+24 V) and 2 (0 V) on the Control Unit. The CU must be powered independently of the Power Module.
• Administrator rights on the PC, required to install the unsigned or WHQL-signed USB driver and to register the PG/PC interface.

Root Cause: Why the USB-Serial Driver Is Missing

The CU230P-2 Control Unit exposes two USB Human Interface Devices on its Mini-USB port: a generic SINAMICS G120 HID-class device and a USB-to-serial bridge based on the FTDI (or, in newer firmware, the Silicon Labs CP210x) chipset. STARTER installs the HID driver automatically when the installer detects a supported Siemens drive family, but the virtual COM port driver is packaged separately inside the STARTER DVD under:

STARTER Installation DVD
 └── Driver
      └── USB
           ├── CP210x_VCP_Win_XP_S2K3_Vista_7
           └── ftdi2xx.inf / ftdibus.inf
└── Starter.exe

If the engineer installs STARTER from a network share or downloaded ISO without selecting the "Install USB driver" custom option, only the HID portion is registered. Windows Device Manager will then show SINAMICS G120 under Human Interface Devices, but Ports (COM & LPT) will be empty and STARTER's Accessible nodes search will return nothing.

A second failure mode occurs on Windows 10 1607 and later: Microsoft disabled automatic installation of unsigned drivers. If the CP210x or FTDI driver on the DVD predates the Windows version (typical for pre-2017 DVDs), Windows silently rejects it. The device appears as Unknown device in Device Manager.

Step-by-Step: Install the USB Driver Without the Installation DVD

The procedure below works whether or not the original installation DVD is available. It uses only files already present on a STARTER installation or downloads from the chipset vendor's signed Windows driver catalog.

1. Verify STARTER is installed. Open the Start menu and confirm SIMATIC Manager or STARTER appears. If absent, run the STARTER setup as Administrator.
2. Connect the CU230P-2 to 24 V at terminals 1 and 2. Wait for the RDY LED to settle (steady green or slow orange, no fault blink).
3. Plug the USB cable from the CU to the PC. Windows will attempt to enumerate two devices.
4. Open Device Manager (devmgmt.msc). Expand Human Interface Devices – you should see SINAMICS G120. Expand Ports (COM & LPT) – if no Siemens USB-Serial Converter (COMx) appears, the virtual COM driver is missing.
5. Locate the driver package:
   • Option A – From STARTER install path: Browse to C:\Program Files\Siemens\Automation\STARTER\Driver\USB or C:\Program Files (x86)\Siemens\Automation\STARTER\Driver\USB. Look for either slabvcp.inf (Silicon Labs CP210x) or ftdibus.inf (FTDI).
   • Option B – From chipset vendor: Download the current signed Windows VCP driver from Silicon Labs CP210x VCP driver or FTDI VCP driver. Pick the x64 build for 64-bit Windows.
   • Option C – From Siemens support: Use the relocation procedure described in SINAMICS G120 CU230P-2 operating instructions (entry 109751321) under "PC connection kit / USB driver relocation".
6. Right-click the unknown device (or the SINAMICS G120 HID entry), choose Update driver → Browse my computer for driver software.
7. Point to the .inf folder selected in step 5. Tick Include subfolders. Click Next.
8. Approve the Windows security prompt to install the driver. If Windows reports a code 52 (digital signature) error, right-click the .inf, choose Properties → Digital Signatures → Details → View Certificate → Install Certificate → Local Machine → Trusted Publishers, then retry.
9. Confirm a COM port is assigned. Device Manager should now show Siemens Automation USB-Serial Converter (COMx) under Ports. Note the COM number.
10. Restart STARTER so it refreshes its interface list.

PG/PC Interface Assignment (S7USB)

With the COM port present, STARTER still requires the PC to bind it to a logical interface called S7USB. Without this binding, STARTER searches only TCP/IP nodes and never sees the local USB link.

1. Open Control Panel → Set PG/PC Interface (the 32-bit Siemens applet, not the modern Windows one).
2. Click Properties on S7USB. The default selection should be USB.
3. If S7USB is missing, click Select..., scroll to S7USB, and add it.
4. Confirm the COM port shown in Device Manager matches the S7USB assignment.
5. Click OK and close the applet.

In TIA Portal / Startdrive, the equivalent binding is in Online → Accessible nodes. The CU will appear with USB icon once the project is recompiled.

Commissioning the CU230P-2 Without a Power Module

A common misconception is that a Control Unit must be docked to a PM to function. For commissioning purposes the CU only needs:

• 24 V at terminals 1/2 (logic supply).
• EP / Enable Pulses terminal 31 driven high (+24 V). The factory default is no enable, so a CU on the bench will refuse to run even though it powers up.

Apply 24 V to terminal 31 and the CU transitions from Ready (off) to Ready (on). Motor terminals U/V/W remain open-circuit because the IGBTs are inside the PM, which is fine for parameter editing and Modbus testing.

Modbus Parameter Setup Over USB

The CU230P-2 HVAC and CU230P-2 BT expose RS485 Modbus RTU on terminals 29/30. With the drive on the bench, you can fully configure the Modbus map and verify register reads without ever running a motor.

Key parameters:

After writing parameters, perform a Copy RAM to ROM (p0971 = 1) so they survive a power cycle on the customer's cabinet.

STARTER vs. Startdrive vs. TIA Portal

Three commissioning paths exist for the G120 family:

• STARTER (legacy) – best for older firmware (V4.x), supports offline projects that open in Startdrive. Project files use .ssp extension.
• Startdrive in TIA Portal (V15+) – required for firmware V4.7 SP3 and later on the CU230P-2. Adds integrated PLC tag exchange and trace recording. Project files use standard TIA Portal format.
• Web server (SINAMICS G120 Smart Access module) – for the G120C and G120 with Web Server option. Not all CU230P-2 variants support it; check the nameplate for WLAN module ordering data.

If commissioning a brand-new CU230P-2 with firmware V4.7 SP10 or higher, Startdrive in TIA Portal is the only path that includes the latest GSD/GSDML files. Older STARTER projects can be migrated using Project → Migrate to TIA Portal.

Verification and Diagnostics

After driver install and PG/PC binding, run this checklist before declaring success:

1. Device Manager check: Ports (COM & LPT) shows Siemens USB-Serial Converter (COMn). HID section still shows SINAMICS G120.
2. STARTER online search: Project → Accessible nodes → S7USB returns the CU's IP/USB identifier within 5 seconds.
3. Online identification: Click Identify. STARTER should display the CU's article number (e.g., 6SL3246-0AE31-...) and firmware version.
4. Parameter upload: Load to PG should succeed without fault F07012 / F08501.
5. Trace buffer: Start a 1-second trace on r899 (status word) – the trace graph must update, confirming live data exchange.

Troubleshooting Matrix

Field Tips and Caveats

• The USB port on CU230P-2 supports hot-plug, but always disconnect STARTER online session before pulling the cable to avoid corrupted parameter blocks.
• When the CU is later installed in the cabinet and powered through the PM, the 24 V external supply must be removed before applying mains to the PM, or ground loops can damage the USB transceiver.
• Never use a USB cable longer than 3 m without an active repeater. The USB-to-serial bridge is sensitive to voltage drop on VBUS.
• If STARTER is installed under a non-default path, search the entire drive for slabvcp.inf or ftdibus.inf with PowerShell: Get-ChildItem -Recurse -Filter *.inf -Path C:\ | Select-String -Pattern 'cp210|slabvcp|ftdibus'.
• For firmware V4.7 SP10 or later, install the Siemens USB driver package separately from the G120 CU230P-2 operating instructions entry under "Software / Tools"; the modern driver includes both CP210x and FTDI bridges.

FAQ