MP370 PROFIBUS Baud Rate Reverts to 12 Mb/s Resolving HMI

Overview

The Siemens SIMATIC MP370 is a 12-inch and 15-inch Touch Panel from the Multi Panel (MP) generation that runs the flexible WinCE / ProTool HMI runtime. It communicates with SIMATIC S7-300 / S7-400 controllers (and a number of third-party masters) over PROFIBUS DP at 9.6 kbit/s up to 12 Mbit/s, and over MPI for programming.

A recurring field symptom is that the bus baud rate is set locally on the MP370 to 1.5 Mbit/s, the panel is rebooted, and the rate reverts to 12 Mbit/s as soon as the project starts. Local control-panel edits are not persistent. They are only valid while no project is running, and the runtime immediately re-applies the bus parameters from the compiled .fwd / .pdb project image at every cold start.

This article documents the underlying mechanism, the supported fix paths inside ProTool / ProTool Pro and STEP 7 + NetPro, the use of ProSave for image backup, and the diagnostic checks required to confirm a clean 1.5 Mbit/s PROFIBUS segment on the MP370.

Problem Details

Symptom (as observed in the field):

1. The operator opens Control Panel → PROFIBUS on the MP370.
2. Transmission speed is set to 1.5 Mbit/s and the new value is accepted (no error returned).
3. The panel is power-cycled or warm-restarted.
4. The PROFIBUS interface re-initialises at 12 Mbit/s.
5. The S7 station either logs DP bus errors (SF on the CPU, BF on the CP) or fails to come online at all because the master is configured for 1.5 Mbit/s but the MP370 is talking at 12 Mbit/s.

Root Cause

The MP370 stores two distinct sources of PROFIBUS configuration:

When the HMI loader has finished loading the project, it calls the DP slave service of the MP370 communication driver and re-programs the SPC3 / ASPC2 / chip-asic used on the MP370 PROFIBUS interface. The values applied are the ones stored in the project, not the values visible in Control Panel.

This behaviour is identical for the MP270, MP370 and MP377 series, and is a deliberate design to guarantee that an HMI matches the bus profile of the S7 station it has been engineered against. Manually setting 1.5 Mbit/s in Control Panel only takes effect if the project has been deleted, the loader cannot find a valid project, or the project was compiled with the bus set to "MPI/DP - automatic".

Two engineering situations trigger the reversion to 12 Mbit/s:

1. STEP 7 / NetPro integrated project: the MP370 is a DP slave of an S7-300 or S7-400. The bus profile is propagated from NetPro to the HMI station by ProTool. If the S7 master is set to 12 Mbit/s (the DP default), the HMI project is regenerated with 12 Mbit/s every time it is re-transferred.
2. Standalone ProTool project: the MP370 is configured as a stand-alone DP slave. The baud rate is set in ProTool under Station → PROFIBUS DP → Bus Parameters. A previously-compiled project with 12 Mbit/s is still on the panel, and the new source was never re-transferred.

PROFIBUS DP Baud Rate Reference

PROFIBUS DP (IEC 61158 / EN 50170) supports a fixed set of transmission rates. The values are derived from a 24 MHz baud-rate generator divided by an integer; not every value is valid.

Reference: PROFIBUS DP specification (EN 50170 Volume 2 / IEC 61158). The 12 Mbit/s value is the default for nearly all modern Siemens DP masters because the segment-length budget (100 m) is sufficient for cabinet-internal wiring and the cycle time overhead is minimal. This is also why the project reverts to it.

Prerequisites

• STEP 7 V5.4 SPx or V5.5 (the MP370 is fully supported up to STEP 7 V5.5 + ProTool Pro 6.0 SP3).
• ProTool / ProTool Pro V6.0 SP2 or later (part of the SIMATIC HMI ProTool package). WinCC flexible 2007 SP3 may also be used for some MP370 images, but the engineering tool that compiled the project must be used to recompile it.
• ProSave V6.x (or the ProSave that ships with the HMI ProTool / WinCC flexible CD). ProSave handles image backup/restore and serial / Ethernet / MPI / USB transfer.
• RS-232 serial null-modem cable (6ES7 901-1BF00-0XA0) or PC adapter USB / MPI (6ES7 972-0CB20-0XA0) for MPI/DP transfer or Ethernet crossover for point-to-point transfer.
• The original STEP 7 / ProTool project source files (the ".s7p" and ".ptp" / ".fwd" pair). Without the source, you can upload the runtime image with ProSave but it cannot be re-compiled.

Solution 1 — Modify the Baud Rate in ProTool and Re-Download the Project

This is the supported path. Do not edit the baud rate on the panel itself; edit it in the engineering tool that produced the project.

1. Open the original .ptp / ProTool Pro project on the engineering station.
2. Open Station → PROFIBUS DP → Bus Parameters.
3. Set Transmission speed to 1.5 Mbit/s (or whichever rate matches the S7 master).
4. Confirm that the DP slave address matches the rotary / DIP switch on the back of the MP370 (default 1, range 1…126). Mismatch will not change the baud rate but will produce a different error.
5. If the MP370 is connected to an S7 master that is engineered in STEP 7, open the S7 project in STEP 7 and double-click SIMATIC 300 Station → Hardware → PROFIBUS DP. The subnet properties show the bus profile. The value must match the value set in ProTool.
6. Save, compile, and select Target → Transfer → MPI / PROFIBUS / Ethernet.
7. Confirm the transfer — the loader stops the runtime, writes the new image, and reboots the MP370.
8. After reboot, open Control Panel → PROFIBUS. The transmission speed should now display 1.5 Mbit/s, and the fieldbus status LED on the master should go green.

Solution 2 — Change Bus Parameters in NetPro (STEP 7 Integrated Project)

For MP370 stations that are part of a STEP 7 project, the bus profile is owned by NetPro, not by ProTool.

1. Open the STEP 7 project in SIMATIC Manager.
2. Open NetPro from the toolbar or via Options → Configure Network.
3. Right-click the PROFIBUS subnet to which the MP370 is attached and choose Object Properties → Network Settings.
4. Change Transmission rate to 1.5 Mbit/s. STEP 7 will warn you if the segment length exceeds the allowable cable distance for the selected rate (200 m at 1.5 Mbit/s, Type A cable).
5. Save and close NetPro.
6. Open the HMI sub-project. The ProTool bus parameters will already be updated to 1.5 Mbit/s.
7. Re-compile the HMI station (HMI Station → Compile and Check All).
8. Transfer the HMI project to the MP370. STEP 7 / ProTool can transfer only the bus parameters, the entire project, or a delta. The full project transfer is recommended the first time after the change.

Solution 3 — Back Up the Current Image with ProSave (Precautionary)

Before any change, take an image backup so the panel can be restored if the new project fails to load. ProSave is the Siemens tool for image backup, restore, and authorised / non-authorised transfers.

1. Connect the PC to the MP370. RS-232 is the lowest-common-denominator path; Ethernet requires the panel to have a fixed IP and the correct routing.
2. Start ProSave from the SIMATIC HMI installation (Start → SIMATIC → ProSave → ProSave).
3. Select Device type → MP370 and the connection type (Serial, MPI, or Ethernet).
4. Set the destination path, e.g. C:\Backup\MP370_image.psb.
5. Click Backup. The image includes the runtime, the project, the registry (including Control Panel settings) and the licence key for any option packages.
6. Verify the resulting file size: a full MP370 image is 32 MB to 64 MB depending on firmware and option packs. A file under 1 MB means the image was not captured correctly.

To restore: select Restore instead of Backup, point to the file, and confirm. The panel will reboot and load the saved image.

Verification

After the project has been re-transferred and the panel rebooted, perform these checks in order:

1. Local control panel read-back. Open Control Panel → PROFIBUS. The transmission speed field must read 1.5 Mbit/s immediately after the project has finished loading (not just after the boot loader phase).
2. Master side acknowledgement. On the S7-300 / S7-400, open the diagnostic buffer (Module Information → Diagnostic Buffer) and look for the "DP slave: MP370, address 1, online" entry. A clean entry with no 0E01/0E02 slave-diagnostics error confirms DP is up.
3. Bus monitor. If a PROFIBUS diagnostic tool (e.g. Acromag ProfiHub monitor or a softing PB-Inspector) is available, attach it to the segment and confirm that the bit time is 667 ns (1 / 1.5 Mbaud) and that no repeat requests are being generated.
4. Cold-restart test. Power-cycle the MP370 three times. On every restart the baud rate must come up at 1.5 Mbit/s, not 12 Mbit/s. A single "12 Mbit/s" reading means the project on flash was not updated.
5. Network → Project comparison. On the engineering station, open the ProTool project and the STEP 7 NetPro subnet properties. The transmission rate in both must match the rate now active on the panel. Mismatch indicates a regeneration problem and the next transfer will revert the panel again.

MP370 Hardware and Firmware Reference

The relevant panel variants and their default PROFIBUS interface:

All variants use the same PROFIBUS ASIC family and share the same 9-pin Sub-D PROFIBUS connector pin-out (pin 3 = B-line, pin 8 = A-line, pin 6 = +5 V bus termination, pin 5 = DGND). The bus terminator is built into the panel and switched in/out by a switch next to the connector. The terminator must be ON for the last device on the segment and OFF for all others.

Cable and Connector Reference

PROFIBUS DP cable specification per IEC 61158 / EN 50170:

Reference: Beckhoff PROFIBUS Cabling Guide. A common field failure mode is crossed A / B lines at one connector, which forces the master to fall back to a lower baud rate, and the panel, with a mis-wired drop, reverts. Always re-check the connector pin-out before assuming a project-level fault.

Troubleshooting Matrix

Diagnostic Procedure When Source Code Is Missing

If the original ProTool / STEP 7 project source is no longer available, the panel can be operated in Control Panel mode only — that is, without a project. In that mode the local baud rate is honoured. This is not a production solution; it is a stop-gap.

1. Use ProSave to upload the current image. Save as MP370_last_good.psb.
2. Use ProSave to delete the project on the panel (Options → Delete project or by restoring an empty image).
3. Set the PROFIBUS parameters in Control Panel → PROFIBUS to 1.5 Mbit/s and the correct DP address.
4. Reboot. The panel will sit at the loader screen; no HMI screens will appear.
5. At the next planned downtime, obtain the original project source (from the machine builder / system integrator) and re-transfer a properly compiled project.

Field-Proven Caveats

• STEP 7 V5.4 vs V5.5: projects that were created in V5.4 SPx and contain an MP370 with a 1.5 Mbit/s profile will re-compile cleanly in V5.5, but the bus parameter will be reset to 12 Mbit/s if the HMI station is regenerated from scratch (delete + re-insert the MP370). Always edit, never re-insert.
• WinCC flexible substitution: WinCC flexible 2007 SP3 can open and recompile some MP370 projects, but the bus profile is mapped differently. Use the engineering tool that originally compiled the project; mixing tools is the most common cause of "transferred but reverts".
• Sub-D connector pinning: pin 6 supplies 5 V from the panel for the bus terminator. If the cable is daisy-chained and the terminator is ON at a middle node, the terminator will load the bus and force a re-negotiation. Many field technicians mistakenly leave the terminator ON at every device.
• Repeaters: a PROFIBUS repeater (e.g. 6GK1 500-3AA00) regenerates the segment but does not change the baud rate. If the master and the MP370 are isolated by a repeater, the baud rate must still match on both sides; the repeater does not translate.
• Fibre-optic segments: an OLM (Optical Link Module) terminates the electrical segment and re-launches the optical one. Both sides must be set to the same baud rate, otherwise the OLM will flag a "baud rate mismatch" and drop the segment.

Related Siemens HMI Behaviour

The same "local edit discarded at runtime start" pattern is observed on the entire MP270 / MP370 / MP377 family and on the OP / TP 270 / 277 series. The fix in all cases is identical: edit the baud rate in the project source, recompile, re-transfer. The Siemens Industry Online Support portal hosts the SIMATIC HMI ProTool / WinCC flexible manuals (entry IDs 1137646, 18658556, 11169480) that document the bus-parameter edit path in detail.

For Multi Panels moving to TIA Portal, the engineering tool is the TIA Portal HMI configuration (WinCC Comfort / Professional). The MP370 is not a TIA-native target, but a TIA-compiled WinCC flexible project can be loaded onto a TP / MP 277 or later panel. If the upgrade path is on the roadmap, it is a good time to fix the baud rate at 1.5 Mbit/s, transfer, validate, and then migrate.

FAQ