TP177B PN/DP Recalibration Failure After OS Update Recovery Guide

1. Problem Overview

The Siemens SIMATIC TP177B PN/DP 6" CSTN operator panel (Order Number 6AV6 642-0BA01-1AX0) is reported to enter a non-recoverable state in the touch calibration utility immediately after a Windows CE / HMI image OS update has been performed. The device boots successfully, the calibration cross appears on the screen, and the operator is asked to touch the five calibration points in sequence. However, the panel fails to advance past the calibration routine, loops indefinitely between the touch prompt and the coordinate-assignment step, and never presents the user with the confirmation screen that normally saves the new calibration data to flash.

This behavior has been reproduced on multiple units (three identical panels reported in a single maintenance event) running Image Version B.1.1.1.0 with Windows CE 3.0, after the image was upgraded to B.1.1.2.1 using WinCC Flexible 2008 SP1 HF5 on a Windows Vista Ultimate SP1 engineering station. The same failure mode has also been documented on the larger 6" TP277 6" color panel from the same product family.

2. Affected Hardware and Firmware

The following table summarizes the configuration that has been confirmed to exhibit the failure. Operators working on variants not listed below should still apply the same procedure, but should verify that the WinCC Flexible version supports the target image.

3. Root Cause Analysis

The TP177B stores the resistive touch matrix calibration in a persistent flash region that is overwritten - but not always re-initialized - during a full image update. When the OS update is performed without first transferring a project (which contains the new calibration block), or when the image is applied with the "Reset to factory settings" option disabled, the touch controller retains stale coefficients pointing to a calibration set that no longer matches the physical touch sensor response curve of the freshly flashed image. The result is a calibration routine that registers touches at coordinates it considers invalid and never advances the state machine.

Three contributing factors have been identified in the field:

1. Missing pre-update reset. The standard Siemens recovery procedure requires that the panel be returned to factory defaults before the new image is transferred. Skipping this step leaves orphan calibration records in the registry-equivalent store.
2. Touch-sensor drift after image reload. The analog front end on the 6" CSTN variant is sensitive to the impedance of the bezel adhesive. After a thermal cycle caused by the OS flash (the panel CPU runs hot during image decompression), the resistive values shift by a small percentage. A calibration performed with the "tap and release" method often fails to register five valid samples in a row.
3. Calibration-utility timeout mismatch. The B.1.1.2.1 image reduced the per-sample dwell timer from 1500 ms to 800 ms to support faster boot. On a slow touch contact, the firmware rejects the sample before the algorithm has a chance to integrate it, causing the routine to restart at the first cross position.

4. Mandatory Pre-Update Procedure

Siemens has published a dedicated entry in the Support database that documents the recovery workflow for the TP177B / TP277 / TP377 series after an unsuccessful OS update. The reference number is FAQ ID 19701610, available at the Siemens Industry Online Support portal:

Siemens FAQ 19701610 - Recalibration after OS update on TP177B / TP277 / TP377

Before flashing the new image, the panel must be placed in delivery state. Use the following sequence:

1. Power the panel off.
2. Hold the CE key (the recessed button above the display on the 6" housing) and power the panel back on.
3. Wait for the loader screen, then release the CE key.
4. From the loader menu select Settings > Reset to factory settings. Confirm with the checkmark.
5. Wait for the panel to reboot automatically. The display will remain at the loader menu after the reset.

5. OS Update Execution

With the panel back at the loader screen and connected via Ethernet (PN) or PROFIBUS DP, the new image is transferred using WinCC Flexible 2008 SP1 HF5:

1. Open WinCC Flexible 2008 SP1 HF5 and select Project > Transfer > OS Update.
2. Browse to the supplied image TP177B_PN_DP_B.1.1.2.1.img (or the equivalent for the target hardware).
3. Enter the panel's IP address (default 192.168.0.1, subnet 255.255.255.0) or its PROFIBUS address.
4. Set the transfer mode to Serial / Ethernet / PROFIBUS as appropriate and click Update OS.
5. Confirm the dialog warning that all data on the panel will be overwritten.
6. Wait for the transfer progress bar to reach 100%. Typical transfer time for the 6" image is 6-8 minutes over a 10/100 Mbit link.
7. When prompted, click Reboot. The panel restarts into the loader and then automatically enters the calibration routine.

6. Recalibration Recovery Procedure

If the panel enters the calibration loop after the image transfer - showing the cross and then returning to the first coordinate - apply the following procedure. It differs from the standard "tap and release" technique documented in the operator manual.

6.1 Hold-and-hold method (recommended)

1. Position yourself squarely in front of the panel. Rest the heel of your hand on the bezel to stabilize the wrist.
2. Place the pad of your index finger on the first cross.
3. Hold the finger in place - do not lift it - for 3 to 5 seconds. The firmware needs to accumulate enough analog samples to validate the contact.
4. The cross will move to the next calibration point while your finger is still in contact. Slide (do not lift and re-touch) the finger to the new position.
5. Repeat the hold for each of the five calibration points. The sequence is: center, top-left, top-right, bottom-right, bottom-left.
6. After the fifth point is held, the panel will display a confirmation dialog asking to save the calibration. Tap the green checkmark.
7. The panel writes the new coefficients to flash and reboots into the project loader.

6.2 Why "tap and release" fails on B.1.1.2.1

The 800 ms dwell timer introduced in image B.1.1.2.1 is shorter than the typical 1.2 - 1.5 s settling time of the resistive touch sensor after a finger lift. The firmware's debounce logic treats a quick tap as a single noisy sample and discards it. The hold-and-hold method forces the firmware into its continuous-sampling mode, where it integrates the analog signal and accepts the touch as valid.

7. Alternative Recovery Paths

If the hold-and-hold method still does not advance past the first calibration point, the issue is more severe than a debounce problem. Try the following in order:

8. Verification and Acceptance Test

Once the panel returns to the project loader, run the following acceptance checks before placing the unit back in service. They verify that the calibration was saved correctly and that the touch controller is stable across the full display area.

1. Draw test: Open the loader menu's Touch test utility (available in image B.1.1.2.1 and later). Drag a line from each corner to the diagonally opposite corner. The line should track the finger with no more than 2 mm deviation at any point.
2. Dead-zone test: Tap at the four corners and at the center of the display. Each tap must register. Any missed tap indicates a calibration point that was not saved.
3. Project transfer test: Transfer the actual runtime project to the panel and verify that the project boots and that operator inputs on the project screens register correctly.
4. Power-cycle test: Power the panel off and on three times in succession. On each boot, the panel must skip the calibration routine and go directly to the project loader or the configured start screen. If the calibration prompt reappears, the calibration data was not committed to flash and Section 6 must be repeated.
5. Communication test: From the engineering station, use WinCC Flexible's Connectivity Station or the panel's Diagnostics page to verify that the configured PROFINET or PROFIBUS connection is up and that the panel exchanges data with the controller.

9. Known Limitations and Edge Cases

Several edge cases have been documented on the TP177B / TP277 / TP377 family that interact with the calibration behavior described above. Engineers responsible for the panel should be aware of the following:

• TP277 6" color variant (6AV6 643-0AA01-1AX0): The 6" color panel in the 277 series has been reported to exhibit the same "no time-remaining indicator" symptom. The OS update procedure in Section 4 and 5 is identical, but the recovery in Section 6 may require the passive stylus approach (alternative path 1) because the color panel's touch sensor is more sensitive to bezel pressure.
• PROFIBUS DP-only variant (6AV6 642-0DA01-1AX0): The image transfer must be performed over MPI/PROFIBUS, not Ethernet. The transfer dialog in WinCC Flexible automatically detects the panel's communication interfaces; verify that DP is selected before clicking Update OS.
• Mixed firmware on a plant: Do not run a TP177B with B.1.1.2.1 alongside a TP177B with the older B.1.1.1.0 if both panels share a single WinCC Flexible project. The runtime version embedded in the project must match the panel image, or the project will fail to load.
• Vista SP1 + HF5 only: The HF5 hotfix specifically addresses a transfer timeout bug that affects Vista-based engineering stations. Installing only SP1 without HF5 will produce a transfer that appears to succeed but leaves the panel in a partially updated state - this is one of the documented root causes of the calibration loop.

10. Related Operator Panel Variants

The same recovery philosophy applies to the wider 177 / 277 / 377 product line. Engineers familiar with one variant can apply the procedure to the others with minor adjustments. The table below summarizes the most common variants and the specific points to watch for.

For a complete overview of the 177/277/377 series, including commissioning notes, refer to the Siemens SIMATIC HMI Operator Panels manual collection in the Industry Online Support portal. The TP177B device manual in particular contains the official calibration procedure that this article extends.