Enabling USB on PCU 50 in SINUMERIK 840D HMI Systems

Enabling USB on PCU 50 in SINUMERIK 840D HMI Systems

1. Overview: Why USB on a PCU 50 Is Not a Trivial Task

The SINUMERIK 840D operator panel stack is built around the PCU 50 (Panel Control Unit 50) — an industrial PC that hosts the HMI software, manages the fieldbus connection to the NCU, and serves as the loader for part programs. PCU 50 hardware revisions shipped between 2001 and 2010 fall into two OS families:

• PCU 50 (original) with Windows NT 4.0 Embedded — does not contain a native USB mass-storage class driver. External USB sticks cannot be enumerated as drives. This is by design; Microsoft never released a production-quality USB stack for NT 4.0.
• PCU 50.3 with Windows XP Embedded (XPe) / Windows Embedded Standard 2009 — full USB 1.1/2.0 mass-storage support out of the box, subject to USB filter/lockdown configuration in the XPe image.

If your shop currently loads NC programs via the floppy disk (1.44 MB) on a PCU 50, the bottleneck is the OS, not the connector. The diagnostic question is therefore always: which PCU 50 revision and which OS image are installed? Everything else follows from that answer. This article covers identification, native USB enablement on XPe-based units, OEM-driver workarounds for legacy NT 4.0 units, mandatory image backup before any driver load, and verification steps that meet Siemens acceptance practice.

2. PCU 50 Model Variants and Identification

The rear-panel type plate reveals the Siemens MLFB (order number), BT (Boot version), and SS (Start-up/Software version). These three data points determine whether USB can be enabled without third-party drivers.

MLFB (6FC5210-0DFxx-...)	OS	HMI Software	Native USB Mass-Storage
6FC5210-0DF00-0AA0 / -0DF01-0AA0	Windows NT 4.0 Embedded	HMI-Advanced (≤ 06.03.xx)	No
6FC5210-0DF02-0AA0	Windows NT 4.0 Embedded	HMI-Advanced (07.xx)	No
6FC5210-0DF30-2AA0 / -0DF31-2AA0	Windows XP Embedded SP2	HMI-Embedded / HMI-Advanced 08.x	Yes
6FC5210-0DF32-2AA0 / -0DF33-2AA0	Windows XP Embedded SP3	HMI-Advanced 08.x / 13.x	Yes
6FC5210-0DF34-2AA0	Windows Embedded Standard 2009	HMI-Advanced 13.x	Yes (EHCI)

2.1 Read the Rear Label

1. Power down the operator panel.
2. Locate the type plate on the rear of the PCU 50 housing.
3. Record:
   • MLFB — Siemens order code beginning 6FC5210-0DF
   • BT — Boot version (e.g., BT 06.03.xx)
   • SS — Software/start-up version (e.g., SS 06.03.xx)
4. Cross-reference against the table above. If BT ≥ 06.03.20 and SS reports "WinXP", proceed to Section 4. If SS reports "WinNT", proceed to Section 5.

3. Pre-Work: Mandatory HMI Image Backup

Before any driver change or HMI reconfiguration, create a complete image of the existing boot volume. This is not optional — a corrupted HMI on a PCU 50 forces a return to Siemens repair or a full re-installation of the XPe image using the original Siemens recovery DVD, which requires the matching SS license code.

3.1 Imaging Procedure

1. Boot the PCU 50 to the HMI desktop (service user, password SUNRISE on legacy units, or the OEM service account on XP units).
2. Insert a blank PCMCIA hard-disk adapter or connect an external USB drive containing an imaging tool (on XPe units only; on NT units use the floppy or a network share).
3. Launch the Siemens Service Center application.
4. Select Backup Image and choose Full Image (System + Data).
5. Save the image to the external medium. Verify the file size matches the source partition (typical PCU 50 system C: partition is 4–8 GB).
6. Label the backup with: MLFB, BT, SS, date, and HMI software version.

3.2 Backup Verification

1. Boot from a known-good rescue media (Siemens Service Stick or WinPE 2.0 USB on XPe units).
2. Mount the image file with the imaging tool.
3. Verify the file structure: \Windows\System32\config\SYSTEM present, \mmc2.dir (HMI-Advanced) or \hmisl.dir (HMI-Embedded) present.
4. Only proceed with USB work after verification.

4. Native USB Enablement on PCU 50 with Windows XP Embedded

If identification confirms a Windows XPe image, USB mass-storage works without driver installation. The remaining work is configuration — disabling USB filters, granting access to non-admin service accounts, and choosing a compatible USB stick.

4.1 Verify USB Stack Status

1. Boot to the XPe desktop.
2. Open Device Manager (right-click My Computer → Manage → Device Manager).
3. Expand Universal Serial Bus controllers. Expected entries:
   • USB Root Hub
   • USB2 Enhanced Host Controller (on units with EHCI)
4. Insert a USB stick. The drive should enumerate within 2–3 seconds; My Computer shows a new drive letter (typically E: or F:).

4.2 Disable USB Write Filter (EWF / FBWF)

XP Embedded on PCU 50.3 typically runs the Enhanced Write Filter (EWF) or File-Based Write Filter (FBWF). The filter protects the C: volume from writes — including any new driver or registry entry from USB enumeration.

Filter	Detection	Disable Command
EWF	ewfmgr c: shows enabled overlay	ewfmgr c: -disable
FBWF	fbwfmgr /displayconfig	fbwfmgr /disable

1. Open Command Prompt (Admin).
2. Run the appropriate disable command.
3. Reboot. The C: volume is now writable; HMI writes will persist.
4. If you must keep write protection, schedule ewfmgr c: -commit after USB operations instead of disabling permanently.

4.3 Configure USB Stick Compatibility

XPe on PCU 50.3 supports FAT16 and FAT32 natively. NTFS-formatted sticks work for read but may fail for write due to missing NTFS write components in the embedded image.

1. Format the USB stick as FAT32 on a separate Windows PC.
2. Use sticks ≤ 32 GB; larger sticks require a different partition table (GPT) that the embedded USB stack does not parse.
3. Prefer sticks with a known USB controller (Phison SMI, or Sandisk OEM controllers). Some low-cost sticks use controllers that misreport on cold boot and are re-enumerated only after warm reset.

4.4 Part-Program Transfer Workflow

1. Insert stick into front-panel USB port of the PCU 50.
2. Wait for the "Found New Hardware" balloon (XPe) and confirm Drive is now ready.
3. Open the HMI-Advanced Services → Network / Data Storage area or HMI-Embedded program manager.
4. Browse to the new drive letter. The default NC program directory is D:\MPF\ (for main programs) and D:\SPF\ (for subprograms) on the HMI drive partition, not C:.
5. Copy .MPF and .SPF files to the local D: partition using the HMI file manager (never Windows Explorer while NCK is online, to avoid file locking conflicts).

5. PCU 50 with Windows NT 4.0 — OEM USB Driver Workarounds

NT 4.0 has no USB stack. Microsoft never published a production USB driver set for NT 4.0; only Windows 98 and later shipped with native USB support. For PCU 50 units running NT, the options are limited and carry real risk.

5.1 The Two Documented OEM Paths

1. Dell OEM USB NT 4.0 driver package — Dell released an NT 4.0 USB supplement for legacy server and workstation lines; some shops have adapted it for PCU 50 hardware. Recognized as "at your own risk" by every installation report on record.

5.2 Pre-Flight Checks Before NT USB Driver Install

1. Confirm the image backup from Section 3 is verified and stored offline.
2. Disconnect the PCU 50 from the NCU network — the driver install can hang the network stack and interrupt NCK communication.
3. Record the current HMI-Advanced version. Compatible versions typically run 06.03.20 through 07.06.xx on NT 4.0.
4. Verify at least 200 MB free on C: for driver staging.

5.3 Installation Sequence

1. Copy the OEM driver package to C:\INSTALL\USB\ from the floppy or network share.
2. Open Control Panel → SCSI Adapters / USB Devices (the exact entry depends on the OEM package).
3. Add USB Open Host Controller and USB Root Hub.
4. Reboot. The system will reload NT 4.0 with the USB stack.
5. Insert the stick. If enumeration fails, try the rear-panel USB ports (different root hub in some PCU 50 layouts).

5.4 Known Failure Modes on NT 4.0

Symptom	Probable Cause	Remediation
BSOD STOP 0x3E (system exception)	Incompatible OEM driver	Boot to last-known-good; remove driver; restore image
USB stick not enumerated	Power-on surge trips USB polyfuse	Remove stick, wait 10 s, reinsert
Drive letter assigned but "not accessible"	NTFS stick on FAT-only driver	Reformat stick as FAT16
HMI-Advanced hang after stick insert	I/O contention with HMI file watcher	Disable HMI file watcher via HMI config, retry
NCU loses connection after driver load	Driver consumed IRQ shared with fieldbus NIC	Reassign IRQ in BIOS; reboot; verify NCK link

6. Recommended Migration Path: Replace NT-Based PCU 50

For production cells where the floppy drive is the bottleneck, the engineering-correct path is not driver hacking but migration to a PCU 50.3 with Windows XP Embedded and the matching HMI-Advanced license. Siemens provides a documented upgrade procedure:

1. Order PCU 50.3 with the same BT/SS family as the existing NCK to maintain version compatibility (NCK software and HMI software must be in the same BT/SS family — see the SINUMERIK 840D sl Compatibility List).
2. Transfer the CF/HDD and license dongle (if applicable) from the old PCU 50 to the new one.
3. Re-image using the Siemens recovery media matching the new SS version.
4. Connect to NCK, verify operator-panel and machine-control responses.
5. Decommission the old PCU 50; retain it as a spare with the verified image backup.

This approach gives full Siemens-supported USB, network, and CF-card support, and avoids any unsupported driver modification.

7. Alternative: Network-Based Program Transfer

If the PCU 50 cannot be replaced and the OEM-driver risk is unacceptable, transfer programs over Ethernet instead. Both NT 4.0 and XPe units ship with TCP/IP and file-sharing.

1. Configure a static IP on the PCU 50 (e.g., 192.168.1.10, mask 255.255.255.0).
2. Enable File and Printer Sharing on the D: volume (the HMI data partition, not C:).
3. From the engineering PC, map a network drive to \\192.168.1.10\D$ (administrative) or to a shared folder.
4. Copy .MPF and .SPF files directly to D:\MPF\ and D:\SPF\.
5. The HMI auto-detects the new files within a few seconds; the program appears in the program manager.

Network transfer works identically on NT and XPe and is supported by every SINUMERIK service document. It is the lowest-risk route off the floppy drive.

8. Verification Checklist

Run all applicable items after any USB-related change.

1. Image backup verified readable (Section 3.2).
2. USB stick enumerated and assigned a drive letter within 3 s of insertion.
3. Drive is readable in Windows Explorer (XPe) or OEM file manager (NT).
4. HMI-Advanced program manager refreshes within 5 s of new file arrival on D:.
5. NCK link remains UP throughout USB operation (check Service → Overview → NCU Connection).
6. Feed hold and override remain responsive during USB I/O.
7. After stick removal, no phantom drive letter remains in Windows.
8. If EWF/FBWF was disabled, re-enable and commit overlay state.
9. Cycle power on the operator panel; verify clean boot to HMI desktop within 45 s.
10. Run a round-trip test: copy a known MPF to the stick on PCU 50, read it back on the engineering PC, and diff against the source.

9. Safety and Compliance Notes

• USB transfer on a running machine must not interrupt any safety-relevant I/O. Siemens HMI-Advanced disables file services while the machine is in Auto mode on many SS versions; confirm the behavior for your SS build before relying on hot transfers.
• USB sticks are an attack vector. Lock down the XPe USB filter to allow only authorized device IDs (VID/PID whitelist), or use the Siemens USB Whitelist Tool shipped with the HMI-Advanced installation media.
• Any unauthorized driver load on a PCU 50 used on a Safety Integrated machine requires re-validation of the operator panel per EN ISO 13849-1 and IEC 61508. Siemens will not sign off on such a modification.
• Always run an image restore drill after the first successful backup. A backup that has never been restored is not a backup.

10. Field-Engineering Summary

1. Read the rear type plate first — MLFB, BT, SS.
2. Image the unit before any change.
3. On XPe PCU 50.3: enable USB by configuring EWF/FBWF and using FAT32 sticks.
4. On NT 4.0 PCU 50: do not attempt to load OEM USB drivers on a production machine. Use network transfer, or migrate to PCU 50.3.
5. Always verify the round-trip — copy, read back, compare bytes.

For the underlying machine integration and SS-family matching, see the SINUMERIK 840D sl Operator Components Manual (06/2012 edition) and the PCU 50.3 Base Software Commissioning Manual. These documents are the binding references for any modification to a PCU 50 in a SINUMERIK 840D installation.