Configuring Siemens OP77A ProSave Backup via USB-PPI Cable

Overview

The Siemens SIMATIC OP77A is a 4-inch monochrome graphics operator panel from the OP 73/OP 77A/OP 77B family, configured with WinCC flexible and backed up / restored using the ProSave utility. The OP77A exposes a single RS-485 (PPI / MPI physical layer) port on the rear of the unit, so a USB-to-RS485 adapter such as the 6ES7 901-3DB30-0XA0 USB-PPI multi-master cable is required to talk to it from a modern PC that has no physical COM port. The cable presents itself as a virtual COM port (typically COM3, COM4, or higher) and bridges USB 1.1/2.0 to the 9-pin sub-D PPI connector on the panel.

This reference covers the full configuration path: setting the Windows PG/PC interface to the correct driver, choosing the proper cable type in the PG/PC interface properties, enabling the serial transfer channel in the OP77A project, putting the panel into transfer mode, and resolving the most common ProSave error dialogs ("No connection could be established" and COM1 baud-rate mismatch on backtransfer).

Prerequisites

Hardware and Driver Installation

1. Plug the USB-PPI cable into a free USB 2.0 port on the engineering PC. Windows will enumerate the cable and request the Siemens USB-PPI driver. If the driver does not auto-install, point Device Manager at the directory C:\Program Files\Siemens\Automation\S7PCT\USB-PPI or use the driver from the WinCC flexible installation media under Drivers\USB-PPI.
2. Confirm the virtual COM port assignment in Device Manager → Ports (COM & LPT). Typical values: USB Serial Port (COM3) or USB Serial Port (COM4). Note the COM number; you will need it for the ProSave backtransfer step.
3. Connect the DB-9 end of the USB-PPI cable to the OP77A. The OP77A uses a male DB-9 on the underside labelled "IF1B" or "PPI/MPI". Tighten the screws.
4. Power the OP77A from 24 VDC; the boot screen should appear within 8 seconds.

Configuring the PG/PC Interface

The PG/PC interface is the Windows-level mapping between a logical Siemens protocol stack and a physical adapter. ProSave and WinCC flexible both read this mapping to know which adapter and baud rate to use.

1. Open Start → Control Panel → Set PG/PC Interface (32-bit). On Windows 10/11 with modern Control Panel, search for "Set PG/PC Interface".
2. In the Access Point of the Application dropdown, select S7ONLINE (Step 7 standard access point). Click Properties in the dialog if it does not auto-populate after the selection.
3. Under Interface Parameterization Used, locate the entry matching the USB-PPI cable. The label is PC Adapter (PPI) or PC/PPI cable (PPI) — do NOT select "Serial cable PPI" because that targets a true hardware COM port, not the virtual COM created by the USB-PPI driver.
4. Open the Properties dialog of the chosen PC/PPI cable. Configure the following:

5. Click OK, then OK again to close the Set PG/PC Interface dialog. The S7Online access point now resolves to the USB-PPI cable.

Activating Transfer Mode on the OP77A

The OP77A will only accept a ProSave download, upload, or backtransfer when it is in transfer mode. There are two ways to enter it:

• Manual transfer mode: Power up the OP77A while holding the bottom-left soft key (key variant) or pressing the centre of the touch area (touch variant). The panel displays "Transfer" and waits for the host.
• Configured transfer mode: In the WinCC flexible project, navigate to Project → Transfer → Settings and enable Serial under Channel. Recompile and download the project. The panel will then accept a transfer at any time during normal operation if the host initiates one within the configured timeout.

Verify the panel is in transfer mode by observing the bottom status bar: it should show the word "Transfer" on a small icon, not "Stop" or "Offline".

ProSave Configuration for Backup and Restore

1. Launch ProSave from Start → SIMATIC → ProSave or from the WinCC flexible installation directory.
2. In the General tab, set the following fields:

3. Click OK to commit. ProSave will attempt a connection test; a green LED icon means the panel is reachable.
4. For a backup: select the Backup tab, choose a target .psb file path, and click Start Backup.
5. For a restore: select the Restore tab, choose a source .psb file, and click Start Restore. The OP77A will reboot into transfer mode automatically during the restore.

Resolving "No connection could be established"

This is the most frequent error dialog. Walk through the following checks in order; each is a common misconfiguration observed in the field.

1. Confirm the OP77A is in Transfer mode and not just powered on with the project running. The status bar must say "Transfer".
2. Re-verify the PG/PC interface: Access Point of the Application = S7ONLINE, Interface Used = PC/PPI cable (NOT "Serial cable PPI" or "USB/PPI multi-master cable" — those entries do not exist for OP77A connectivity; the historical Siemens forum guidance to select "USB/PPI multi-master cable" was superseded by the "PC Adapter (PPI)" entry once the unified PC/PPI driver shipped).
3. Open the Properties of the PC/PPI cable and confirm Local connection = USB and PPI address of the PG/PC = 0. Many users leave the address at 1, which collides with the panel.
4. Re-seat the DB-9 connector at the OP77A. The PPI port is on the underside and is easy to leave half-inserted.
5. Try a different USB port. Some USB 3.0 hubs on Windows 10 do not enumerate the USB-PPI driver correctly; use a root hub port.
6. Check that no other software (e.g. a live WinCC flexible runtime) has already opened the same COM port — only one process can own the port.

Configuring the PPI Address of the OP77A

The PPI address of the OP77A itself can be set from the panel's service menu when no project is loaded, or in the WinCC flexible project under Project → Transfer → Settings → Bus Parameters → PPI Address. Factory default is 1. If you re-address the panel, update the Partner address in the PG/PC interface to match.

Backtransfer (Reverse Engineering)

Backtransfer reads the project that is currently running on the OP77A back to the PC. It uses the same USB-PPI cable but a different ProSave tab:

1. In ProSave select the Backtransfer tab.
2. Set the destination file path. ProSave writes a .pdz (compressed project) or .pdl (uncompressed) file.
3. Click Start Backtransfer. ProSave resets the panel into transfer mode and pulls the compiled project across the PPI bus at 115200 baud. The process typically takes 30-90 seconds for a 256 KB project.

Troubleshooting Matrix

Verification

1. From ProSave, click Connection Test (or watch the status icon turn green) — this confirms the PG/PC interface, COM port, baud rate, PPI addressing, and the physical cable are all healthy in one step.
2. Run a Backup of the current panel state to a known file path. The resulting .psb should be between 64 KB and 512 KB depending on project size. A near-zero file means the connection failed mid-stream.
3. On the OP77A status bar, confirm the panel returned to its normal operating screen (not stuck in "Transfer"). A clean exit to runtime proves the protocol handshake completed.
4. Re-deploy the backed-up .psb to a second identical OP77A to confirm the file is valid. A successful restore round-trip is the strongest end-to-end verification.

Field-Proven Cautions

• Do not hot-plug the USB-PPI cable while ProSave is mid-transfer. The PPI bus is sensitive to re-enumeration glitches and ProSave will abort the backup silently.
• If the OP77A has been re-flashed or is brand new with no project, the backtransfer step is not available — there is no project to read. Use the WinCC flexible Download workflow instead.
• The USB-PPI multi-master cable is electrically isolated, but the OP77A's 24 VDC supply must share a common ground reference with the engineering PC through the USB shield, otherwise the RS-485 transceiver will not see valid logic levels on long cable runs.
• Always keep a current .psb for every OP77A on site. The ProSave backup is the only sanctioned way to migrate a panel to a new display if the original WinCC flexible source has been lost.