Resolving PC Adapter USB A2 Missing from SIMATIC Manager PG/PC

Problem Description

Engineers report that after installing the Siemens SIMATIC PC Adapter USB A2 (catalog number 6ES7972-0CB20-0XA0) on a programming device, the adapter is fully recognized by the Windows operating system, yet it does not appear in the dropdown list inside SIMATIC Manager → Options → Set PG/PC Interface. The interface list either shows only PC Adapter (MPI) or PC Adapter (Auto) without any USB variant, or it shows PC Adapter (PPI) only.

Confirmation that the driver is installed but not registered for STEP 7 is obtained by verifying these three facts:

• Windows Device Manager lists SIMATIC PC Adapter USB under the “SIMATIC” or “Universal Serial Bus controllers” branch with no yellow warning icon.
• Add or Remove Programs (Windows XP) or Programs and Features (Windows 7 / 10) shows the “SIMATIC PC Adapter USB” or “S7USB” driver as installed.
• Adapter LEDs illuminate correctly when the USB cable is plugged into the PC and the MPI/PROFIBUS connector is seated on the PLC.

When the interface does not appear in the SIMATIC Manager dropdown, the engineer cannot establish an online connection to the S7-300 or S7-400 CPU, cannot download hardware configuration, and cannot run diagnostic functions such as PLC → Monitor/Modify. Restoring this entry is a prerequisite for any online engineering workflow.

Background: PC Adapter USB A2 Hardware and STEP 7 Architecture

The PC Adapter USB A2 is Siemens’ second-generation USB-to-fieldbus programming adapter. It supersedes the legacy RS-232 PC Adapter (6ES7972-0CA20-0XA0) and supports MPI, PROFIBUS DP master class 1/2, PPI, and Freeport (RS-232 level) protocols from a single Type-A USB 2.0 host interface.

STEP 7 V5.5 communicates with the adapter through a layered architecture. The Windows kernel driver S7USB.sys exposes the adapter to user mode, where the S7USBAPI.dll provides the application interface. SIMATIC Manager and the Set PG/PC Interface tool enumerate available interfaces by reading the registry tree under HKLM\SOFTWARE\Siemens\AUTSW (32-bit Windows) or HKLM\SOFTWARE\Wow6432Node\Siemens\AUTSW (64-bit Windows). If the driver is installed in the wrong bitness context, the registry tree is missing, and the dropdown list will be empty for the USB variant.

MPI/PROFIBUS 9-Pin Sub-D Connector Reference

Because the symptom is sometimes confused with a cabling issue, keep the following pinout handy when triaging on-site. The PC Adapter USB A2 ships with a captive cable terminated in a 9-pin female sub-D plug.

The bus segment must be terminated at both physical ends with 220 Ω resistors between pins 3 and 8, with a 390 Ω pull-up to pin 6 and pull-down to pin 5. Active PROFIBUS connectors (e.g. 6ES7972-0BA30-0XA0) embed this termination; passive drop connectors do not.

Root Cause Analysis

The symptom “driver installed but invisible to SIMATIC Manager” has four documented root causes. Apply the troubleshooting matrix below to triage before applying solutions.

Pre-Diagnostic Checklist

Confirm each item before opening the registry. The total time for this checklist is typically under five minutes.

1. Open Windows Device Manager and expand SIMATIC or Universal Serial Bus controllers. Verify “SIMATIC PC Adapter USB” appears without a yellow bang.
2. Right-click the device → Properties → Driver. Note the Driver Version and Provider (“SIEMENS AG”). Expected versions: 6ES7 972-0CB20 driver ≥ V2.0 for STEP 7 V5.5 SP4; ≥ V2.2 for TIA Portal V13+.
3. Confirm the version of SIMATIC Manager: open Help → About. The build number should be ≥ 5.5.0.0 (with SP4 = 5.5.4.0 or higher).
4. Try a different USB port, preferably directly on the motherboard (avoid USB hubs and docking stations). USB 3.0 ports in legacy mode are usually compatible, but some KVM switches block bulk transfers.
5. Plug the adapter into a known-good PLC or MPI repeater and verify the yellow Active LED blinks within five seconds.
6. Verify the OS bitness: Control Panel → System → System type. If “64-bit Operating System” is reported, the issue is most likely the 32/64 mismatch covered in Solution 1.

Step-by-Step Diagnostic Procedure

Follow this ordered sequence to identify the failing layer quickly.

1. Check the “Set PG/PC Interface” dropdown contents: open SIMATIC Manager → Options → Set PG/PC Interface. Read every entry exactly as displayed. If “PC Adapter (USB)” appears but is greyed out, the driver is loaded; the problem is the access point mapping (Root Cause 4).
2. Inspect the registry tree: open regedit. On a 64-bit OS, launch the 32-bit registry editor from C:\Windows\SysWOW64\regedit.exe so the Wow6432Node tree is visible. Navigate to HKLM\SOFTWARE\Siemens\AUTSW\PGPCInterface (32-bit OS) or HKLM\SOFTWARE\Wow6432Node\Siemens\AUTSW\PGPCInterface (64-bit OS). If the Interfaces subkey is missing, the driver was not registered through STEP 7.
3. Compare bitness: in 64-bit Windows, open File Explorer → C:\Windows\System32 and confirm the file PGPCInterface.exe is present. Also check C:\Windows\SysWOW64. The version of STEP 7 V5.5 is always 32-bit; the executable in SysWOW64 is the one SIMATIC Manager actually uses. If the System32 copy was launched by mistake from the Start menu, no USB entries will be visible.
4. Verify the S7USB driver file: in %SystemRoot%\System32\drivers (32-bit OS) or %SystemRoot%\SysWOW64\drivers (64-bit OS), confirm S7USB.sys exists with a version stamp ≥ 2008. A missing file indicates the kernel-mode component was never installed.
5. Check the Windows event log: Event Viewer → Windows Logs → System. Filter for source S7USB or DeviceInstall. Errors with codes 51, 52, or 53 indicate resource conflicts (typically IRQs) that prevent the kernel driver from binding.
6. Test with a clean user profile: create a local Windows user, log in, install STEP 7 only, and try the dropdown. If the USB entry appears, the original profile has corrupted registry overrides under HKCU\Software\Siemens.

Solution 1: Resolve the 32-bit vs 64-bit PG/PC Interface Mismatch

This is the single most common cause of the symptom on any Windows version above XP. STEP 7 V5.5 is a 32-bit application regardless of the host OS. The PG/PC Interface tool that it invokes must therefore be the 32-bit build. On 64-bit Windows, two PG/PC Interface executables exist:

The Windows Start menu shortcut Start → SIMATIC → STEP 7 → Set PG/PC Interface should launch the correct (32-bit) executable. If the user or another tool has overridden the shortcut or if a 64-bit shortcut was pinned by mistake, the wrong binary is launched. Verify by right-clicking the shortcut → Properties → Target. The target must point to PGPCInterface.exe inside the STEP 7 installation path, typically C:\Program Files (x86)\Siemens\Automation\SimaticManager\PGPCInterface.exe or C:\Program Files\Siemens\… on a 32-bit OS.

If the target is correct and the dropdown is still empty, force the correct binary:

1. Close SIMATIC Manager.
2. Open an elevated command prompt (Run as Administrator).
3. Launch the 32-bit tool directly: "C:\Program Files (x86)\Siemens\Automation\SimaticManager\PGPCInterface.exe"
4. Confirm the dropdown now contains PC Adapter (USB).
5. If yes, recreate the Start-menu shortcut to point to this binary.

On 64-bit Windows, the corresponding registry path that STEP 7 uses to enumerate interfaces is HKLM\SOFTWARE\Wow6432Node\Siemens\AUTSW\PGPCInterface\Interfaces. Missing or mismatched subkeys in this 32-bit view will not be visible to Set PG/PC Interface even when the 64-bit view appears correct. Use the SysWOW64 regedit.exe to confirm the entries are present:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Siemens\AUTSW\PGPCInterface\Interfaces\PC Adapter (USB)]
"DLL"="s7ubpapx.dll"
"Device"="S7USB"
"BaudRate"=dword:00007530
"Timeout"=dword:00007530

Edit the baud rate (default 0x7530 = 30 000 decimal, the internal “auto-detect” marker) and timeout in decimal when configuring manually. Do not modify this key unless the STEP 7 setup cannot be re-run; a typographical error here will silently break the dropdown.

Solution 2: Reinstall the USB A2 Driver Through STEP 7 Setup

The driver must be installed via the STEP 7 setup wizard, not through Windows Update or a standalone INF. Installing outside the wizard registers the kernel driver but does not populate the STEP 7 registry tree or the “Access Point” configuration.

1. Open Control Panel → Add or Remove Programs (XP) or Programs and Features (Windows 7 / 10).
2. Uninstall SIMATIC PC Adapter USB if present.
3. Unplug the USB A2 from the PC.
4. Insert the STEP 7 V5.5 DVD (or mount the ISO). Run Setup.exe with administrator rights.
5. Select Install → Select user-defined installation.
6. In the component tree, expand SIMATIC Software → STEP 7 → PC Adapter / USB and ensure “SIMATIC PC Adapter USB” is checked. The tree on a fresh install lists: PC Adapter (MPI) → PC Adapter (PROFIBUS) → PC Adapter (PPI) → SIMATIC PC Adapter USB. The last item is the USB A2 entry; the previous three are protocol mappings for the legacy RS-232 PC Adapter.
7. Complete the wizard and reboot when prompted.
8. Plug the adapter back in. Windows should detect the device and use the driver installed in step 6.
9. Reopen SIMATIC Manager → Set PG/PC Interface and verify the dropdown now lists PC Adapter (USB).

Solution 3: Repair the USB Driver Stack and Windows INF Cache

If the adapter is visible in Device Manager but the dropdown remains empty, the kernel driver may have a stale binding or a corrupted INF cache. Apply the following in order:

1. Unplug the adapter.
2. Open Device Manager → View → Show hidden devices.
3. Under Universal Serial Bus controllers, uninstall any greyed-out “SIMATIC PC Adapter USB” instances.
4. Under SIMATIC, uninstall any entries referring to the USB adapter.
5. Delete cached files: %SystemRoot%\INF\setupapi.dev.log (do not delete the setupapi directory itself). Also remove %SystemRoot%\System32\DriverStore\FileRepository\s7usb*.inf_* directories.
6. Reboot. Reconnect the adapter. Windows Plug-and-Play will rediscover it.
7. Re-run Solution 2’s STEP 7 setup if Device Manager still reports the driver generically or as “Unknown device”.

For deeper corruption, run the Microsoft Program Install and Uninstall Troubleshooter to scrub residual driver entries, then reapply Solution 2. On Windows 7 64-bit systems that have been upgraded in-place from XP, leftover XP-signed driver packages frequently prevent the newer S7USB driver from binding—a clean reformat and reinstall is sometimes faster than incremental repair.

Solution 4: Manually Register the Access Point and Interface Assignment

If the dropdown shows entries other than USB, or the USB entry is present but greyed out, manually remap the access point “S7ONLINE” to the USB interface using the PG/PC Interface dialog:

1. Open Set PG/PC Interface from SIMATIC Manager.
2. Select Interface Parameter Assignment Used → PC Adapter (USB).
3. Click Properties… and configure the parameters below.

4. Click OK → OK to confirm. STEP 7 will write the new mapping to HKLM\…\AUTSW\PGPCInterface\Access Points\S7ONLINE.
5. Restart SIMATIC Manager for the change to take effect on the online dialog.

If the PC Adapter (USB) entry still does not appear, the registry tree itself is missing. The fastest recovery is to import a known-good export from a peer system. Export the Interfaces and Access Points subkeys from HKLM\SOFTWARE\Wow6432Node\Siemens\AUTSW\PGPCInterface on a working machine, then import on the affected PC after uninstalling the driver and re-running Solution 2.

Verification: Going Online and Reading Diagnostics

After applying any of the solutions above, verify the fix by performing an online test.

1. Connect the USB A2 to the PC and to the MPI/PROFIBUS port of the S7-300 CPU. Power on the PLC.
2. Open SIMATIC Manager → Options → Set PG/PC Interface. Confirm PC Adapter (USB) is the selected access point.
3. Open the STEP 7 project for this PLC. From the project tree, right-click the S7-300 station → Target system → Online → Display.
4. The Online view should populate within 5–10 seconds at 187.5 kbps. If a “Connection to partner cannot be established” message appears, the bus is not the issue—return to Solution 4.
5. Open PLC → Diagnostic / Setting → Operating Mode. Confirm the CPU reports its expected order number, e.g. 6ES7 315-2EH14-0AB0 V4.x.
6. Click Accessible Nodes (PLC → Accessible Nodes). The CPU’s MPI address (default 2) should appear in the list within the configured timeout.

For a hardware-level verification independent of STEP 7, run the Siemens PC Adapter USB Diagnostics Tool (separate install, available from the STEP 7 Tools folder under Start → SIMATIC → STEP 7 → NCM S7 → PC Adapter USB Diagnostics). The tool loops a test pattern over MPI and reports PASS/FAIL plus signal quality, isolating cable, connector, and bus-termination issues from the driver configuration.

Working with Multiple Adapters on One PC

When a single engineering workstation drives more than one bus (e.g., an MPI machine network and a separate PROFIBUS DP segment), STEP 7 supports up to four PC Adapter USB instances simultaneously. Each instance is differentiated by a USB serial number rather than a COM port.

1. Open Set PG/PC Interface and select PC Adapter (USB).
2. Click Properties… → tab Adapter.
3. Tick Different adapter for each access point and assign each access point (e.g., S7ONLINE_MPI, S7ONLINE_DP) to a specific adapter by serial number.
4. Create additional access points from Options → Set PG/PC Interface → Access points → Add.

Symptom cross-check: if only one of the two adapters shows in the dropdown, the second adapter’s driver has been installed in a non-STEP 7 context (Windows Update). Re-run Solution 2 for the missing instance.

Working with Virtual Machines and Remote Engineering

Engineers increasingly run STEP 7 inside a Windows VM (VMware Workstation, Hyper-V, VirtualBox) hosted on a Linux or modern Windows workstation. The PC Adapter USB A2 must be passed through to the guest OS:

• VMware: VM → Removable Devices → SIEMENS AG SIMATIC PC Adapter USB → Connect (Disconnect from Host). Then install Solution 2 inside the guest.
• Hyper-V: Use Enhanced Session Mode; USB passthrough requires the host to be Windows 10/11 Pro or Enterprise. Add the adapter under Hyper-V Manager → USB settings.
• VirtualBox: install VirtualBox Extension Pack; Devices → USB → SIEMENS AG SIMATIC PC Adapter USB.

Cable, Connector, and Bus Termination Diagnostic

If Solution 1–4 restore the dropdown but the online test still fails, the issue has migrated from driver to physical layer. Use this checklist:

1. Inspect the 9-pin sub-D shell for bent pins (most often pin 4 RTS or pin 7 P24V).
2. Measure >20 V DC between pins 7 and 2 of the bus connector with the PLC powered. The USB A2 cannot supply 24 V; the PLC is the source. A reading below 18 V indicates an under-powered bus or a backplane supply fault.
3. Confirm termination at both bus ends only. A third terminator in the middle of the segment reflects the wave and causes intermittent errors, not a hard “adapter missing” symptom—but combined with a marginal cable it can mask driver issues.
4. Substitute a known-good PROFIBUS cable. Siemens 6XV1830-0AH10 (purple, 1 m) is a useful diagnostic spare.
5. Cycle power on the PC and PLC. Hot-plugging the USB A2 with the PLC in RUN can leave the device in a state that only a cold reboot clears.

Migration Path to TIA Portal

The PC Adapter USB A2 hardware is supported by both STEP 7 V5.5 and TIA Portal V13 onward, but the driver signing and installer changed with TIA V13. If your engineering fleet is moving to Windows 10 / 11:

1. Run the TIA Portal V16 (or later) installation media with user-defined installation; select PC Adapter USB driver in the component tree.
2. Verify the new Set PG/PC Interface (TIA Portal → Options → PG/PC Interface) lists PC Adapter (USB).
3. Retire STEP 7 V5.5 installations from the same machine to avoid dual-driver conflicts (Solution 2 in reverse).
4. If a mixed fleet is unavoidable, install the latest combined driver package (S7USB V2.2 or later) which serves both V5.5 SP4+ and TIA Portal V13+.

For more details on TIA Portal compatibility, consult the official Siemens Industry Online Support portal, where the latest release notes for TIA Portal list the supported operating systems and the bundled PC Adapter USB driver version.

Preventive Configuration and Rollout Standards

To prevent recurrence across an engineering fleet, codify the following as a deployment SOP.

1. Standardise on STEP 7 V5.5 SP4 or later when PC Adapter USB A2 is the programming tool. Earlier service packs lack signed drivers for Windows 7 SP1 64-bit.
2. Always run the STEP 7 setup with “user-defined installation” and explicitly check SIMATIC PC Adapter USB. A typical install path on a 64-bit OS deploys only the 64-bit subset, which leaves the 32-bit registry tree empty.
3. Avoid Windows Update for the USB A2 driver. Pin the SIEMENS-supplied version in the driver store by setting Device Installation Settings → No (“Never install driver software from Windows Update”) under System Properties → Hardware.
4. Document the access point mapping: every engineering laptop should have S7ONLINE mapped to PC Adapter (USB) for direct MPI/DP work, or to TCP/IP → Network card for routing through a NetLink or IE/PB Link. Switching between the two requires only the dropdown selection, not a re-install.
5. Maintain a known-good USB cable for diagnostics: 3 m USB 2.0 A-to-A with ferrite beads at both ends. Cable degradation is a frequent misdiagnosis that mimics a driver problem.
6. For Windows 10 / 11 retrofits, use the TIA Portal V16+ PC Adapter USB driver package. Legacy V5.5 drivers do not load cleanly on Windows 10 1809+. Plan a migration to TIA Portal if the engineering fleet is on Windows 10.
7. Back up the registry tree on every machine after a successful install: regedit → export HKLM\SOFTWARE\Wow6432Node\Siemens\AUTSW (32-bit view) → save as .reg. This backup is the fastest restore path when Solution 4 is required in the field.

Frequently Asked Questions