Troubleshooting Siemens OP73 OS Update Transfer Connection

Overview

The SIMATIC OP73 micro is a 3-inch monochrome text/graphics HMI panel from the Siemens SIMATIC HMI family. It is a low-cost operator interface used on small machines, often paired with S7-200 (CPU 21x, 22x) and S7-1200 CPUs over PPI/MPI. Despite its simple front-end, the OP73 runs a proprietary real-time operating system stored in flash memory, and that OS is version-stamped against the WinCC Flexible / TIA Portal project that you compile. When the compiled version of device embedded in the project does not match the firmware image flashed on the panel, the panel refuses the download with the diagnostic string: "Download is not possible. The version of the device in your WinCC flexible project and the version of the operating system of the device are not compatible."

The standard recovery path is the OS Update procedure (Project → Transfer → OS Update, with optional Reset to factory settings). The OS Update repaints the panel's flash with the image embedded in the engineering project, and from there the device-version check passes. The catch is that the OS Update itself travels over the same physical cable and protocol stack as a normal project download. If the cable cannot sustain the higher transaction density (or the larger image size) demanded by the OS update, the panel hands you a second fault: "A connection could not be established. Please check your settings, ports, cable etc. The executed action was not successful." This article walks the field engineer through that exact failure chain, isolates the cable-type root cause that the original integrator hit, and lays out a verified OS-update procedure that survives mixed PC/hardware environments.

Problem Symptoms and Error Chain

The reported fault surfaces in three distinct stages. Each stage is generated by a different subsystem, and reading them in order pinpoints the broken layer.

If the panel stops at Stage 1, the OS Update has not even started. The error is informative, not destructive. If the panel stops at Stage 2, the OS Update wiped user flash and is sitting in its bootloader, which means you must finish the transfer; the panel is now an inert terminal until the new OS image is delivered. If the panel stops at Stage 3, the engineering PC cannot bring up a clean PPI/MPI session to the bootloader, and the panel will not auto-recover - the operator will see a blank screen or a stuck boot message until the link is re-established.

Root Cause: Cable Type Mismatch

The reporter was using catalog cable 6ES7 901-3BF00-0XA0, the legacy PC/PPI cable with an integrated RS-232-to-RS-485 converter on the PC end and a PPI/MPI connector on the panel end. The cable itself is not defective; it is electrically correct for PPI, but it behaves poorly in OS-Update mode for two reasons:

1. RS-232 ↔ RS-485 converter latency. The 6ES7 901-3BF00-0XA0 is an asynchronous serial converter with no flow-control handshake. The OS Update pushes a continuous, full-duplex image stream to the panel bootloader. If the PC's COM port is a USB-to-serial bridge (FTDI, CH340, CP210x), the converter's internal buffers overflow under sustained write load and the panel times out the session.
2. PPI mode vs. MPI mode. The OP73 accepts both PPI and MPI on the same DB-9, but the OS Update bootloader negotiates a higher MPI baud rate (187.5 kbaud) by default. The 6ES7 901-3BF00-0XA0 in its default DIP-switch position runs PPI at 9.6 kbaud or 19.2 kbaud. WinCC Flexible's transfer dialog will silently downgrade the connection to the cable's maximum, but the OS bootloader does not always honour the same downgrade and rejects the session.

The original integrator confirmed the diagnosis by switching the engineering environment to WinCC Flexible 2005 and transferring over a true MPI cable (catalog 6ES7 901-2BB00-0XA0 or the modern USB PC Adapter 6ES7 972-0CA10-0XA0) with the panel's MPI/DP port set to MPI mode. The download completed and the OS Update took effect. The same panel, same firmware image, same PC - only the cable and the protocol mode had changed.

OP73 Hardware and Interface Specifications

Before selecting a cable, confirm that the panel you are talking to is actually an OP73 micro. The OP73 micro (catalog 6AV6 640-0BA11-0AX0) is mechanically and electrically distinct from the OP73 mono (3-inch, catalog 6AV6 640-0AA11-0AX0) and from the larger OP77 series. The differences matter for the transfer path.

Two important constraints flow from the table:

• The OP73 micro has only one physical port (IF1). The PC, the S7 PLC, and any other MPI peer all share that bus. If the S7 CPU is connected during an OS Update, the panel bootloader will see the CPU's MPI traffic and abort. Disconnect the PLC tap from the MPI bus before performing an OS Update.
• The panel's flash is 128 KB. The OS image is loaded into a temporary staging area and then committed. If the staging area is corrupted by a power loss, the panel must be re-staged - which requires the same cable that just failed. Plan the OS Update for a window with stable power.

Compatible Cable Catalog Numbers

Siemens ships several physically similar but logically distinct transfer cables. The wrong choice is the single most common reason for a Stage-3 connection failure on the OP73.

Pre-Transfer Configuration Checklist

Before launching the OS Update, validate the following eight items. Each is a one-minute check that has been field-proven to break the OP73 OS Update silently.

1. Panel power supply is stable. The OP73 draws ≈ 200 mA at 24 V DC. Brown-outs during the staging write brick the panel. Verify with a multimeter at the panel's power terminals (rated 24 V DC ±20%).
2. PLC is disconnected from IF1. Pull the MPI cable from the PLC side or the panel side. The OP73 must be the only MPI peer during the OS Update.
3. Cable DIP switches (if any) are set for the correct mode. On the 6ES7 901-3BF00-0XA0, switch 1 selects PPI vs. free-port, switches 2-3 select baud, switch 4 selects master/slave. For an OS Update set: switch 1 = OFF (PPI), switches 2-3 = ON-ON (19200), switch 4 = ON (master) - or follow the silkscreen on the back of the cable.
4. COM port is real or bridged cleanly. In Windows Device Manager, confirm the COM port assigned to the cable is shown without a yellow warning. If you are on a USB bridge, set the COM port's Latency Timer to 1 ms in the FTDI/CH340 advanced properties; this is the single largest cause of Stage-3 failures.
5. WinCC Flexible transfer channel is set to IF1 / PPI / 19200 (or MPI / 187500). The dialog is at Project → Transfer → Transfer Settings. The PC station address must be unique on the bus (default 0 works). The panel station address must match the address in the project's connection table (default 1).
6. Windows firewall and any COM-port-locking utility (e.g., Hyperterminal, PuTTY left open) is not holding the COM port. Close every other process that may have opened the port.
7. The project on the PC contains the matching version of device. Open Project → Device Version and note the value. Compare to the panel's Control Panel → Info → OS Version screen. They must match exactly for the post-update project download to succeed; the OS Update itself will accept either direction (upgrade or downgrade).
8. Set the panel's Control Panel transfer channel to match. On the panel: Control Panel → Transfer → Channel 1 → PPI, 19200, Address 1 (or MPI, 187500, Address 1). The panel and the engineering tool must agree on at least two of {protocol, baud, address}.

Step-by-Step OS Update Procedure

The procedure below uses WinCC Flexible 2008 as it was the version on the original failure report. Substitute the menu paths for your toolchain if you are on a newer release.

1. Open the project that targets the OP73. Verify that the Devices & Networks editor shows the OP73 with the correct order number (6AV6 640-0BA11-0AX0) and the correct firmware version (for example V01.02.00.00_02.33 as in the original report).
2. Compile the project: Project → Compiler → All (Rebuild). A clean compile is required because the OS image is embedded in the compiled download file (\*.fwx or \*.pwx).
3. Open the transfer dialog: Project → Transfer → Transfer Settings. Set the mode to Serial (USB-PPI or PC Adapter USB), select the COM port, and confirm the baud and protocol match the panel.
4. Test the connection: Project → Transfer → Available Nodes / Status. The OP73 should appear as a node with its MPI address. If it does not, stop and re-do the cable checklist before proceeding to the OS Update.
5. Open the OS Update dialog: Project → Transfer → OS Update. Tick Reset to factory settings only if you want the panel's user flash to be wiped (recipes, passwords, project) at the same time. For a first attempt leave it un-ticked; you can always re-run with the tick enabled.
6. Confirm the prompt. WinCC Flexible will warn that the panel will reboot. Click Update.
7. Reboot the panel when prompted ("Please boot the HMI device..."). On the OP73, this is a power-cycle: turn the 24 V supply off for 5 seconds, then on. The panel will come up in its bootloader with a blank or "Waiting for OS Update" screen.
8. Click Update OS in the WinCC Flexible dialog (it becomes active once the panel reports ready). The progress bar advances; the typical transfer takes 60-180 s depending on the cable and baud.
9. Wait for the panel to reboot automatically into the new OS. The OP73 splash screen will display the new version of device.
10. Run a normal project download: Project → Transfer → Transfer. The original Stage-1 error should be gone.

Equivalent procedure with ProSave (alternative host)

If the OS Update is required as a one-off and you do not want to license a full WinCC Flexible seat for the panel, use the standalone ProSave utility (shipped with WinCC Flexible / TIA Portal, also available as a free download with the panel's HSP). ProSave gives the same OS Update command without the project overhead.

1. Launch ProSave, select OP73 micro as the device type, set the COM port, baud and protocol.
2. Click Device → Reboot to put the panel into the bootloader.
3. Click OS Update → Update OS and select the OS image file (extracted from the WinCC Flexible install media, typically under ...\Support\Images\OP73\).
4. Wait for completion. The official Siemens knowledge base entry Operating System Update (OS Update) (entry ID 19701610) covers the ProSave flow in chapters 2 and 3 and is the authoritative reference for any connection-establishment question during the update.

WinCC Flexible Project Device Version Compatibility

WinCC Flexible 2008 - the version the original report used - was the first release to introduce explicit version of device stamping on the OP73. The two values available in the dialog were v1.3.0.0 and v1.4.0.0. The mapping to the actual panel firmware is:

WinCC Flexible 2005, the version that ultimately succeeded in the original report, does not have the device-version check at all - it always pushes the embedded OS image and then the project. That is why the Stage-1 error disappears when you re-compile the same project in 2005. For a clean engineering lifecycle, modernise the toolchain to TIA Portal V17 or later with the corresponding HSP, which carries the OP73 in its compatibility list and removes the legacy 2005/2008 ambiguity.

Verification and Commissioning Tests

After the OS Update completes and the project downloads cleanly, run the following four checks to confirm that the panel is fully recovered.

1. Version parity check. On the panel: Control Panel → Info → OS Version. On the PC: Project → Device Version. The two values must match exactly. A drift of a single digit means the OS Update accepted but the project is still pinned to an older image; re-run the normal project download.
2. Cyclic PLC tag test. Create a single Tag in the project mapped to a MW0 in the connected S7 CPU, attach it to a numeric I/O field on the OP73, and watch the value change online. The OP73 ↔ S7 link over PPI is the most sensitive test of the bus termination; if this works, the rest of the project will work.
3. Recipe round-trip (if the project uses recipes). Save the recipe to the panel, power-cycle the panel, and verify the values reload. The OS Update wipes user flash on a Reset-to-factory-settings run, so this is a positive test of the new image's persistence layer.
4. Alarm log persistence. Trigger a configured alarm, acknowledge it, power-cycle, and confirm the alarm re-appears in its last state. If the alarm is gone, the OS image lost the persistent-alarm flag - re-run the OS Update with Reset to factory settings to reinitialise the alarm subsystem cleanly.

Troubleshooting Matrix

The matrix below maps the most common OP73 OS Update symptoms to the layer in the system that is actually at fault and the corrective action.

Field-Proven Caveats and Engineering Notes

• Never mix two transfer sessions. Closing the WinCC Flexible transfer dialog and re-opening it does not always release the COM port cleanly. A second OS Update attempt on the same COM port can hang the host driver. Fully exit WinCC Flexible between attempts.
• The PC Adapter USB is hot-pluggable; the PC/PPI is not. Always plug the USB cable into the PC before opening the transfer dialog, and let Windows finish enumerating the COM port (the audible USB chime and the Device Manager refresh) before clicking Transfer.
• Siemens support entry 19701610 (Operating System Update - PDF) is the canonical reference for the OS Update procedure on the OP73 / OP77 / TP170-class panels. The entry also covers the Stage-3 "connection could not be established" error and lists the cable requirements verbatim.
• WinCC Flexible 2008 is end-of-life. Use it only for legacy rebuilds. New projects should be created in TIA Portal with the latest HSP for the OP73 micro. The OS Update procedure is identical in TIA Portal: Online → HMI Device Maintenance → OS Update.
• Forgotten panel passwords are resolved with the Reset to factory settings tick on the OS Update. There is no other password-recovery path; the OP73 has no hardware reset button.
• Bus topology. The OP73 has a single DB-9 with pinout conforming to the Siemens PPI/MPI standard (pins 3 = data B, 8 = data A). Standard PROFIBUS cable (6XV1 830-0EH10, violet) is the right cable to use, even for PPI, because of its defined impedance (150 Ω) and shielding.

Inline diagnostic flow

FAQ