Resolving TP177 Micro ProSave Connection Failure with PC Adapter

The Siemens SIMATIC TP177 Micro is a compact 6-inch mono/STN touch HMI panel that remains widely deployed in legacy S7-200, S7-300, and S7-400 installations. Backing up its project (recipe data, screens, alarms, password tables) requires the ProSave utility distributed with WinCC flexible 2008 or earlier. Field engineers frequently encounter a situation in which the PC Adapter USB (6ES7 972-0CB20-0XA0) and the PC Adapter USB A2 (6GK1 571-0BA00-0AA0) work flawlessly against an S7-200 CPU or an S7-300 MPI port, yet cannot establish a connection to the TP177 Micro. This article explains the electrical and protocol reasons for that failure and documents the supported cable alternatives.

1. Problem Statement

Symptom observed in the field:

• ProSave launches and the device type is set to TP 177 Micro (6-inch).
• The Connection dropdown is set to Serial (or Serial (via USB)).
• The Interface parameter points to PC Adapter (PPI) or PC Adapter (MPI).
• After clicking Backup > Restart, ProSave reports: "Connection to device failed," "Error 8010: The interface is not installed," or "Timeout while connecting to HMI."
• Identical cable and PC Adapter combination uploads/downloads from an S7-200 (PPI) without error.

This asymmetry — the cable works on a CPU but not on the HMI — is the diagnostic fingerprint of the missing bus-power issue described in §3.

2. TP177 Micro Hardware and Interface Specifications

The TP177 Micro (MLFB 6AV6 640-0BA11-0AX0 and related variants) is a small-panel member of the SIMATIC HMI family. Relevant interface characteristics for backup operations:

3. Why the Standard PC Adapter USB Fails on the TP177 Micro

Siemens PC Adapters (6ES7 972-0CB20-0XA0, 6GK1 571-0BA00-0AA0, 6GK1 571-1AA00-0AA0 = A2 successor for PROFINET, etc.) are not self-powered from the PC's USB. They derive their bus-side power from the 24 V DC supplied by the S7 CPU across the MPI/DP cable. Concretely:

• Pin 2 / Pin 7 of the Sub-D carry the RS-485 A/B differential pair.
• Pin 6 (or pin 5 + 6, depending on revision) returns the 24 V reference that the CPU sources.
• The S7-200 PPI port sources 24 V, the S7-300/400 MPI port sources 24 V; the TP177 Micro does not.

With no DC link voltage present on the D-sub, the PC Adapter's internal DC/DC converter cannot start, the RS-485 transceiver remains tri-stated, and ProSave either hangs on Searching for device or aborts with an interface-not-ready error. The same ProSave configuration that immediately finds a CPU therefore times out on a panel.

This is not a Windows driver issue and it is not a ProSave version issue — it is an electrical incompatibility. The PPI protocol itself is the same; what is missing is the supply rail that the adapter expects.

4. Compatible Cable Options for TP177 Micro Backup

Siemens explicitly supports two cable classes for transferring ProSave images to/from the TP177 Micro:

4.1 USB-PPI Multi-Master Cable

Order number 6ES7901-3DB30-0XA0. This cable draws its 5 V from the laptop's USB port and generates an internal logic-level supply, so the D-sub does not require external 24 V. The cable is a true multi-master PPI adapter: it can be the only bus master, which is exactly what a stand-alone HMI needs.

4.2 RS-232 / MPI Multimaster Cable

Legacy 6ES7 901-0BF00-0AA0 (RS-232 to MPI, 5 m) or 6ES7 901-1BF00-0AA0 (USB-to-RS232 converter plus 6ES7 901-0BF00-0AA0 in some kits). The original cable requires a real COM port on the PC. Newer laptops without a 9-pin D-sub must use a USB-to-serial converter, but only one that Siemens-tested — third-party converters frequently fail to deliver the required RTS/CTS timing.

4.3 PC Adapter USB — When It Will Work

The PC Adapter USB (6ES7 972-0CB20-0XA0) and PC Adapter USB A2 (6GK1 571-0BA00-0AA0) can be used to talk to an HMI only when the panel is networked into an MPI segment that already has a powered node. In other words: the bus must be energized somewhere upstream. A TP177 Micro on its own, with no CPU and no active MPI repeater, will not provide that 24 V, and the PC Adapter will not come up. This is why field engineers report a confusing pattern where the same cable works on a populated line and fails on an isolated panel.

5. Cable Selection Matrix

6. Pre-Commissioning Checklist

Before launching ProSave, verify each item below. Skipping one of these items is the most common cause of repeated connection failure.

1. Confirm the panel is powered up and the start-up counter / boot screen has reached the project-loading phase.
2. Set the HMI's MPI/PPI address either to the default (1) or to a known value — the TP177 Micro ships with MPI address 1 and 187.5 kbit/s.
3. Verify the panel's transfer mode is enabled: Start Center > Settings > Transfer > MPI/PPI = ON. If the project locks transfer, you must press the Transfer button on the touch screen until the dialog closes before ProSave can attach.
4. Install the cable's driver. The 6ES7901-3DB30-0XA0 cable installs as a virtual COM port (e.g., COM4). The PC Adapter USB installs as a Siemens-specific PPI/MPI device.
5. Close any other applications that may be holding the COM port (Step 7 Micro/Win, TIA Portal, HyperTerminal, PuTTY).
6. Confirm the laptop is not in a power-saving state that disables USB selectively (Windows Device Manager > USB Root Hub > Power Management > uncheck Allow the computer to turn off this device to save power).
7. For Windows 7/8/10, run ProSave as Administrator if the project lives in C:\Program Files\Siemens\ or another protected folder.
8. If you must use Windows 7 or later, install the legacy PC Adapter USB driver package from the Siemens support page 66579062 — newer Windows builds drop the original 2008-era drivers unless the package is sideloaded.

7. Step-by-Step Backup Procedure with ProSave

This procedure assumes the USB-PPI Multi-Master cable (6ES7901-3DB30-0XA0) and a TP177 Micro on its own (no CPU connected).

1. Connect the cable's USB end to the laptop; allow Windows to enumerate the virtual COM port. Note the COM number from Device Manager.
2. Connect the D-sub end to the TP177 Micro's MPI/DP port. Tighten the screws.
3. Power the HMI (24 V DC). Wait for the Start Center to appear.
4. On the touch screen, press Transfer. The Start Center will close and a status bar reading Waiting for transfer will display. This is mandatory — without this step, ProSave cannot interrupt the running project.
5. On the laptop, launch ProSave (Start > SIMATIC > ProSave > ProSave).
6. In the Device type drop-down, choose TP 177 Micro and confirm the device version matches the panel's firmware (6-inch monochrome or 6-inch color).
7. In the Connection field, select Serial.
8. In the Interface field, select the virtual COM port created in step 1 (e.g., COM4: USB-PPI).
9. Set Baud rate to 187.5 kbit/s (the panel's default MPI baud).
10. Set Node address to 0 for the PC; the panel stays at 1.
11. Choose the Backup tab.
12. Specify a destination folder and file name (default extension *.psb for ProSave backup).
13. Click Start Backup. ProSave establishes the MPI handshake, transfers the project, and reports Transfer complete in the status bar.
14. Verify the backup file size: a typical TP177 Micro project is 200 kB – 1.5 MB. A backup of a few kilobytes indicates a transfer that aborted mid-stream.

8. ProSave Configuration Parameters Reference

9. Windows Operating System and Driver Considerations

The TP177 Micro generation pre-dates the broad Windows 10/11 rollout. The following operating-system caveats apply:

• Windows XP SP3: Full native support for every PC Adapter, every PPI cable, and every legacy ProSave build. Siemens still recommends XP for first commissioning of legacy panels when the project archive may have been written years earlier.
• Windows 7 (32/64-bit): USB-PPI 6ES7901-3DB30-0XA0 works with the in-box USB-serial driver. The PC Adapter USB requires the legacy driver from SIOS entry 66579062. Disable driver signature enforcement if the installer complains.
• Windows 8 / 8.1: PC Adapter USB may refuse to start because the USB-PnP enumeration changed. Use compatibility mode or run the installer in Windows 7 compatibility mode.
• Windows 10 / 11: The PC Adapter USB A2 (6GK1 571-0BA00-0AA0) is the only one with native Win10 in-box drivers. For older adapters, a virtual Windows XP machine (Hyper-V, VirtualBox, or VMware) is the most reliable workaround for a WinCC flexible 2008 toolchain.

Symptom: ProSave on Windows 10 displays the COM port but stays at Searching for device. Resolution: switch the virtual machine's COM port to a USB passthrough of the cable, or move the entire ProSave session to a Windows XP/7 host.

10. Troubleshooting Matrix

11. Alternative Path: Legacy PG with Native RS-232

If the only available machine is a Siemens Field PG (e.g., Field PG M2 / M3 / M4) with a real RS-232 port, the original RS-232 Multimaster cable 6ES7 901-0BF00-0AA0 will operate the TP177 Micro without needing any bus-power source from the panel. The cable draws its 5 V from the PC's PS/2 or USB tap on some revisions. Steps:

1. Plug the 9-pin female end of the cable into the Field PG's COM1.
2. Plug the 9-pin male end into the TP177 Micro.
3. Run Set PG/PC interface and select PC/PPI cable (PPI).
4. Set the baud rate to match the panel (default 9.6 kbit/s for PPI, 187.5 kbit/s for MPI).
5. Run ProSave and follow the standard backup procedure.

This is the configuration the original poster attempted and reported as still failing. In that scenario the most common residual cause is that the cable was not the multimaster variant but a non-Siemens USB-to-serial adapter. Always use the genuine Siemens MLFB for legacy panel work.

12. Verification

To confirm a successful backup:

1. Compare file size of *.psb against a known-good project: deviation > 20 % usually indicates partial transfer.
2. Open the *.psb in WinCC flexible using Project > Retrieve to confirm the file is uncorrupted.
3. Cross-check the panel's Start Center version string against the project header to confirm a bit-exact match.
4. Run the restored project in the simulator: Start > Simulation in WinCC flexible. If screens and tags populate, the backup is good.

To confirm the cable itself: connect the USB-PPI Multi-Master cable to an S7-200 CPU. If Micro/WIN uploads a project, the cable is functional. If Micro/WIN also fails, the cable is defective — not the panel.

13. Field-Proven Best Practices

• Keep one USB-PPI Multi-Master cable (6ES7901-3DB30-0XA0) in the field service kit. It is the lowest-friction path to any legacy SIMATIC panel.
• When a customer has no original project, immediately capture a backup before any firmware change or re-compile. The panel's internal project can be reloaded, but if the panel is bricked, only the *.psb file can save the situation.
• Always store the backup in a project-versioned folder: PSAVE_PANELNAME_YYYYMMDD.psb. Multiple captures from the same panel often differ by recipe data and runtime version.
• Document the panel's MPI address and baud rate on the cabinet door. A field engineer arriving cold will lose an hour otherwise.
• If the customer PC has neither serial nor legacy USB, the cleanest path is a Windows XP virtual machine with native COM-passthrough, not a Windows 10 host with third-party serial converters.

14. Summary of the Resolution

Yes — the cable 6ES7901-3DB30-0XA0 (USB-PPI Multi-Master) is the correct choice. It is bus-powered from the PC's USB and does not depend on the 24 V supply that the TP177 Micro does not provide. The original PC Adapter USB (6ES7 972-0CB20-0XA0) and PC Adapter USB A2 (6GK1 571-0BA00-0AA0) fail in this topology because the panel is electrically passive on its D-sub. Once the USB-PPI Multi-Master cable is in use, the ProSave backup proceeds as documented in §7.