OP77B MPI Transfer Failure: WinCC Flexible Troubleshooting

1. Problem Statement

When commissioning a SIMATIC OP77B operator panel from a PG/PC running WinCC Flexible 2008 SP2 / SP3 / SP4 / SP5 over a direct MPI/DP cable, the transfer dialog appears to start normally: WinCC Flexible compiles the project, prompts for transfer mode on the panel, the operator manually switches the OP77B into transfer mode, and the compile/download begins. After several seconds the dialog terminates without an HMI-side status message and without writing the project image. No Event Log entry is generated, and the OP77B continues to display its previous project (or the startup screen).

This silent failure pattern is distinctive. It almost always indicates one of three classes of problems:

1. PG/PC interface mismatch — WinCC Flexible is bound to the wrong logical access point or to a network adapter that is not the one connected to the OP77B.
2. Bus physics error — missing or duplicate termination, wrong cable type, or a baud-rate mismatch on the RS-485 segment.
3. Wrong transfer channel selected in the project — the project is configured for IF1A (MPI/DP) but the OP77B is set to IF1B (RS-232) or vice-versa, or the panel's local MPI address conflicts with the PG.

The proven field workaround for the direct-link configuration is to switch the transfer path to RS-232 (IF1B) using a null-modem cable. The rest of this document explains both the proper MPI setup and the verified RS-232 fallback.

2. OP77B Hardware Reference

The OP77B is a 4-inch monochrome STN operator panel in the SIMATIC HMI Compact family. Two variants exist, both relevant to transfer troubleshooting.

IF1A is the sub-D female 9-pin connector used for MPI/PROFIBUS-DP. The OP77B ships with an integrated bus terminator that is active when the panel is the only or last physical node on the segment, and inactive when an intermediate node.

IF1B is the sub-D male 9-pin RS-232 port. On the OP77B it is dedicated to serial transfer, serial printer, or barcode reader, depending on the project configuration.

For full hardware documentation, refer to the SIMATIC HMI device manual: SIMATIC HMI OP 77B Operating Instructions (A5E00276643).

3. Transfer Path Matrix

WinCC Flexible 2008 supports four transfer paths to the OP77B. Each requires a specific cable, a specific connection setting in WinCC Flexible, and matching hardware switches on the device.

The OP77B does not have an Ethernet interface. Any project referencing Ethernet or PROFINET as the HMI connection will fail compile with error 0x8004xxxF in WinCC Flexible.

4. PG/PC Interface Configuration for MPI

The most common root cause of silent MPI transfer failure is that WinCC Flexible is reading the wrong access point of the application. Follow this procedure exactly before debugging anything else.

4.1 Set the S7ONLINE access point

1. Close WinCC Flexible.
2. Open Start → Control Panel → Set PG/PC Interface (Windows XP) or Start → Siemens Automation → Set PG/PC Interface (Windows 7).
3. In the Access Point of the Application dropdown, select S7ONLINE.
4. In the Interface Parameter Assignment Used list, select the physical interface matching your cable:
   • USB cable → PC Adapter (MPI) -> local or PC Adapter (PROFIBUS) -> local (whichever baud rate the OP77B expects).
   • CP 5611 A2 → CP5611 (MPI) -> local or CP5611 (PROFIBUS) -> local.
5. Click Properties and verify the following:

4.2 Wire the PC Adapter USB

The PC Adapter USB is a 6-pin PROFIBUS connector with a USB pigtail to the PG. The adapter's internal MPI/DP switch (if present on the older non-A2 variant) must be set to MPI for 187.5 kbps operation. The PC Adapter USB A2 (6GK1 571-1AA00) auto-detects.

• LED USB lit: driver enumerated.
• LED Active flashing: MPI token activity detected on the segment.
• If neither LED lights, reinstall the SIMATIC PC Adapter USB driver from the support package: SIMATIC PC Adapter USB — Driver & Documentation.

4.3 Set the WinCC Flexible connection

1. Open the project, select Project → Transfer → Connections.
2. Double-click the active HMI connection (default name Connection_1).
3. Configure as follows:

5. Cable and Bus Physics

5.1 PROFIBUS cable specification

For 187.5 kbps a standard PROFIBUS DP cable (purple, 6XV1 830-0EH10) is acceptable up to 1 000 m segment length. For a two-node PG ↔ OP77B segment of under 5 m a generic shielded twisted pair is normally adequate, but always verify with the PC Adapter USB diagnostics at 187.5 kbps.

5.2 Termination

The PROFIBUS segment must be terminated at both physical ends. In a two-node direct-link configuration (PG ↔ OP77B) the PC Adapter USB has no on-board terminator; the OP77B's internal terminator must therefore be active.

• OP77B DIP switch block S1 on the rear of the unit: switch 1 (R-T) must be ON when the OP77B is the bus end-node and no terminator is plugged into the IF1A connector.
• If you attach an external PROFIBUS terminator plug (6GK1 500-0DA00), set switch 1 OFF.

6. OP77B Transfer Mode Procedure

The OP77B must be placed into transfer mode before WinCC Flexible can write. There is no automatic detection on a serial-only segment.

1. Apply 24 V DC to the OP77B; allow the project to load to the screen or the loader to time out.
2. Press the ESC + K1 + K7 keys simultaneously and hold for ~2 s. The OP77B displays the system menu.
3. Navigate to Transfer and confirm with Enter.
4. The OP77B displays the message Connect to host... on the lower status line and waits for MPI traffic.

Reference: SIMATIC HMI OP 77B Operating Instructions, section 6.4 "Transfer mode".

7. Root Cause Catalog for Silent MPI Failure

The following table maps the symptom (silent abort) to root cause and verification step.

8. RS-232 Fallback Procedure (Verified Workaround)

When the direct MPI link cannot be stabilised in the available time, switch the transfer path to RS-232 (IF1B). This path is single-master (no bus physics) and works in all known OP77B firmware revisions.

8.1 Required hardware

• Null-modem (cross-over) RS-232 cable: 6ES7 901-1BF00-0XA0 (Siemens) or any DB9-male-to-DB9-female cross-over with pins 2 ↔ 3, 4 ↔ 5, 6 ↔ 20 crossed and shield bonded at one end only.
• A real COM port on the PG, or a USB-to-RS-232 adapter based on the FTDI FT232 or Silicon Labs CP210x chipset (avoid Prolific PL-2303 HXA — incompatible with WinCC Flexible serial transfer).

8.2 Null-modem pinout

8.3 Configure the WinCC Flexible project for serial transfer

1. Open the project, Project → Transfer → Connections.
2. Edit the HMI connection; under Type select Serial.
3. Set the COM port to match the PG (e.g. COM1 or COM4 for a USB-to-serial adapter).
4. Set Baud rate to 19200 or 38400 (default is 19200; the OP77B supports up to 38400 on IF1B).
5. Recompile the project: Project → Compiler → All.

8.4 Configure the OP77B serial channel

1. On the OP77B, open the Control Panel via ESC + K1 + K7.
2. Select Transfer → Serial.
3. Set Interface to IF1B, baud rate to the same value as WinCC Flexible.
4. Confirm and place the OP77B in Transfer mode.

8.5 Execute the transfer

1. In WinCC Flexible, choose Project → Transfer → Transfer to device (or click the toolbar Transfer button).
2. WinCC Flexible will prompt Please activate transfer mode on the device. The OP77B is already in transfer mode from step 8.4.
3. Progress bar advances; transfer completes in 30–90 s for a typical 500 kB project.

9. S7 Routing Alternative

If the OP77B is connected to a SIMATIC S7 CPU via MPI and a network bridge is required (for example, the PG sits on Ethernet and must reach the OP77B through an S7-300 PN), then S7 routing must be enabled in the project. Direct-link transfer does not involve routing — there is no router node between PG and OP77B.

Routing requires:

• The intermediate CPU must support routing (all S7-300 CPUs with PN interface and all S7-400 CPUs).
• In NetPro, the OP77B connection and the S7 connection to the CPU must both exist with route entries.
• The PG access point must point at the Ethernet side of the network.

Reference: S7 routing — Functions and Configuration.

If the documentation you are following talks about S7 routing in the context of a direct PG ↔ OP77B link, the documentation is irrelevant to your topology. Skip it.

10. Verification Checklist

After every transfer (MPI or RS-232) verify the following on the OP77B before declaring success:

1. OP77B reboots automatically and displays the configured start screen.
2. Project tree shows the new project under OP77B → Project Files; modify date matches the transfer.
3. On the OP77B, open Control Panel → Information → Project Version and verify it matches the WinCC Flexible Project → Properties revision number.
4. If the project uses a serial printer, send a test print to confirm IF1B is still operational.
5. Cycle power to the OP77B and confirm the project survives a cold restart (no backup battery is present on OP77B — projects are stored in flash; verify no 0x8004xxxx boot errors).

11. Diagnostic Flowchart

The decision logic for the direct-link failure can be reduced to the following sequence.

12. Field-Proven Edge Cases

12.1 USB-to-serial adapters

The original OP77B firmware (V01.01.00) is sensitive to the COM-port numbering. If WinCC Flexible lists the adapter as COM10 or higher, the legacy transfer DLL may reject the port. Force the adapter to COM1–COM4 through Windows Device Manager → Port Properties → Advanced → COM port number.

12.2 Mixed baud rates

If the WinCC Flexible project was last opened in TIA Portal and exported as a *.hmi archive, the default transfer baud may have been reset to 1.5 Mbps for newer panels. Force 187.5 kbps manually before transfer.

12.3 MPI segment with a third node

If a third MPI node (CPU, drive, other HMI) is present, ensure that the highest station address is set to at least (highest physical address + 1), otherwise the PG may fail token arbitration without surfacing an error. With one PG and one OP77B, 15 is always safe.

12.4 Laptop docking stations

Many laptop docks route USB through an internal hub that conflicts with the SIMATIC PC Adapter USB driver. If the PC Adapter USB enumerates correctly on battery power but disappears when docked, the dock is the cause. Connect the adapter to a directly-attached laptop port.

13. Reference Parameters Quick Lookup

14. Summary

Silent MPI transfer failure on an OP77B direct link is a configuration or bus-physics problem in roughly 80 % of cases, not a hardware fault. The verification ladder is:

1. OP77B physically in Transfer mode.
2. WinCC Flexible Connection matches the configured channel (MPI for IF1A, Serial for IF1B).
3. PG/PC Interface → S7ONLINE bound to the correct physical adapter at 187.5 kbps with PG address 0.
4. Bus terminator active at the OP77B end.
5. If all four fail, switch to RS-232 (IF1B) — this path is independent of S7DOS and of the access-point bindings and is the proven field workaround.

15. FAQ