Resolving SIMOREG 6RA70 Offline Detection in DriveMonitor

Problem Overview

When commissioning a fleet of SIMOREG DC Master 6RA70 drives with DriveMonitor software, the most common field symptom is that the tool reports the drive as Offline even though the converter electronics are energized, the PMU shows a healthy state (for example o7.0 "Operation enable, ready"), and no fault is pending. Because DriveMonitor is the only Siemens tool that can read and write the full SIMOREG parameter tree on a single point-to-point RS232 connection, an offline state blocks all parameter upload / download activity and stalls commissioning for every drive on the line.

The root cause is rarely a fault inside the drive itself. In the overwhelming majority of cases, the offline state is the result of one or more of the following: (1) a serial cable wired as a straight-through or with TXD/RXD reversed, (2) a mismatch between the bus address on the drive (USS parameter, default 0) and the address expected by DriveMonitor, (3) a baud-rate or parity mismatch between DriveMonitor and the drive's USS parameter, (4) the wrong COM port selected in DriveMonitor, or (5) a USB-to-serial adapter enumerated above COM9, which DriveMonitor 5.x cannot open.

Resolving the issue requires only a few minutes once the three layers of configuration (cable, drive parameters, DriveMonitor project) are checked in sequence. The remainder of this document describes each layer in detail, in the order an engineer should validate them. For the underlying SIMOREG DC Master hardware reference see the SIMOREG DC Master 6RA70 operating instructions.

SIMOREG 6RA70 Communication Architecture

The SIMOREG 6RA70 is a fully-digital armature- and field-controlled DC drive family covering approximately 6.3 kW to 2500 kW. Communication with the outside world is implemented in three independent layers:

• PMU — the on-board parameterization unit with a seven-segment display and tactile keypad, used for local commissioning without any external tool.
• X300 — a 9-pin Sub-D connector on the front of the electronics box, carrying an asynchronous serial interface that supports RS232 (point-to-point) or RS485 (multi-drop) for USS protocol.
• CBP / CBP2 option module — a plug-in card on the electronics board that adds PROFIBUS DP-V1 and is mandatory for integration into a SIMATIC S7 master via PROFIBUS.

For DriveMonitor parameterization on a maintenance laptop, only the X300 path is relevant. The CBP slot is bypassed entirely. DriveMonitor does not read PROFIBUS drives on X300 — it talks USS to the drive's own serial front-end.

The X300 connector is galvanically isolated from power circuits by an internal DC/DC converter. The serial transceiver inside the drive operates at 5 V TTL levels and is conditioned to RS232 line levels by an onboard transceiver. The same connector doubles as the connection for the OP1S operator panel, the handheld SIMOREG commissioning terminal, and the DriveMonitor cable. The pin assignments below apply to all firmware revisions up to and including 5.4.x.

X300 Serial Interface Pinout

The factory wiring for a SIMOREG X300-to-PC RS232 cable is summarized below. Pin numbers refer to the female X300 connector on the drive and the male DB9 on the PC.

The only three active signal pairs for DriveMonitor traffic are: TXD → RXD (X300-3 to DB9-2), RXD → TXD (X300-7 to DB9-3), and the common ground (X300-5 to DB9-5). The hardware handshake lines (RTS/CTS) can be looped back on the PC side as a 7-8 jumper so DriveMonitor does not have to wait for the drive to assert CTS before transmitting.

RS232 Cable Construction and Verification

For a maintenance setup, build the cable as a 3-wire plus shield assembly using shielded twisted-pair or shielded multi-conductor cable no longer than 15 m. The following procedure produces a robust cable that has been used on production lines with hundreds of drives.

1. Strip back 30 mm of outer jacket on both ends and fold the braid back to form a shield pigtail.
2. Solder the active pairs: X300-3 → DB9-2, X300-7 → DB9-3, X300-5 → DB9-5.
3. On the PC-side DB9 connector, install a 7-8 jumper (RTS to CTS loopback) so the host always claims "ready to send".
4. Connect the shield pigtail to X300 pin 1 (chassis ground) and leave the DB9 housing disconnected from the shield, or use a separate drain wire to pin 5 on the DB9 to avoid ground loops between PC chassis and drive chassis.
5. Verify each connection with a continuity tester before plugging into a live drive.
6. Confirm no shorts exist between any adjacent pins on both connectors — in particular X300-3 to X300-5 and DB9-2 to DB9-5.
7. Slide heat-shrink over each solder joint and label both ends of the cable (e.g. "PC end" / "DRIVE end") to prevent future field mistakes.

Testing the Cable Without a Drive

Before going to the cabinet, verify the cable on a bench with a multimeter and a known-good USB-to-serial adapter. A useful self-test is the loopback procedure:

1. Disconnect the cable from any drive.
2. Short X300-3 to X300-7 with a wire jumper.
3. Plug the DB9 into the PC.
4. Open any terminal emulator (PuTTY, Tera Term, or the Windows mode command) at 9600 baud, even parity.
5. Type any characters. Each character you send must echo back on the terminal screen.
6. Remove the X300-3 / X300-7 short. Characters typed should no longer echo.

If echo works with the short and stops without, the wiring is correct and the ground is solid. If echo is garbled, check parity and baud rate. If echo is silent even with the short, check TXD/RXD orientation on the PC connector.

Drive-Side USS Parameter Configuration

Before DriveMonitor can handshake with the 6RA70, the drive's own USS communication parameters must be set correctly. The parameter numbers depend on firmware version; the table below covers the two most common firmware loads on a working drive and uses the high-700s parameter block used by the 6RA70 communication subsystem.

If the drive has been parameterized previously from a master PLC or panel and the bus address is unknown, temporarily set the address to 0 on the PMU before connecting DriveMonitor. DriveMonitor's "automatic address scan" expects addresses in the 0-31 range and defaults to address 0. After confirming online access, restore the original address.

Reading and Writing Parameters From the PMU

Use the on-board PMU to verify the bus address when the drive is offline to DriveMonitor. The procedure is identical for any parameter in the 6RA70:

1. Press the P key to enter parameter mode.
2. Type 780 and press the green check mark.
3. The display shows the current value of P780 (e.g. 0).
4. Press the green check mark again to enter edit mode.
5. Use the arrow keys to change the value, then press the green check mark to confirm.
6. Press the red X key to exit parameter mode.

Repeat for P781 through P785 as required. DriveMonitor will reflect any parameter change immediately on its next polling cycle (typically 200-500 ms).

DriveMonitor Online Connection Setup

After the cable is built and the drive-side parameters are set, configure DriveMonitor as follows. This procedure works on DriveMonitor 5.2.1.1 through 5.4.2 and is the path that resolves the offline state in the vast majority of cases.

1. Open DriveMonitor and create a new project. Select Unit Type: SIMOREG DC Master.
2. Under Unit Version, choose the firmware build reported by the drive's PMU (e.g. 1.8, 2.1, 3.2). If unsure, leave the version blank — DriveMonitor reads the actual version from the drive once online.
3. Set Technology to None for a generic 6RA70. Technology-specific choices (e.g. Winder, Hoist) only become active once DriveMonitor is online and the matching option board is fitted.
4. Set the USS Bus Address to match P780 (typically 0 for a single drive on RS232).
5. Set Number of PZD to match P783 (typically 2 for standard SIMOREG operation).
6. Open the menu Tools → Online Settings. Configure:
   • Bus Type: USS
   • Interface: COM1 (or the COM number assigned to your USB adapter, remapped to COM1-COM4 if necessary)
   • Baud rate: 9600
   • Bus operation: Automatic
7. Open File → Set Up an USS online connection. Click Start.
8. If the parameters and cable are correct, DriveMonitor displays the connected drive, the firmware version, and the parameter number range. Click Open to load the parameter tree.

At step 7 the bottom status bar of DriveMonitor turns green and shows the drive firmware string. If it remains red or shows "Offline", re-check the cable first (TXD/RXD), then the bus address (P780), then the COM port assignment. Most failures trace back to one of these three layers.

Step-by-Step Commissioning Procedure

The following end-to-end procedure resolves the offline state and provides a repeatable path for commissioning a fleet of identical 6RA70 drives in series.

1. Energize the converter electronics with the 24 V control supply. Confirm the PMU displays a healthy drive state (e.g. o7.0 for "Operation enable, ready" or o1.0 for "Switch-on inhibit"). The drive does not need to be running — DriveMonitor communicates with the electronics regardless of whether the armature supply is on.
2. Note the drive's bus address from P780 (or temporarily set it to 0 for the first connection).
3. Connect the serial cable between the PC's COM port and the drive's X300.
4. Start DriveMonitor. Build the project with the correct unit type, unit version, address, and PZD count.
5. Open the Online Settings dialog. Verify the COM port and baud rate. Click Test — DriveMonitor reports either "OK" or an error code.
6. Click Start in the online connection dialog. The status indicator turns green on success.
7. Click Open to load the parameter tree. DriveMonitor reads the parameter dump from the drive.
8. To upload the live parameter set, open Drive → Upload to PG/PC. The full parameter list is saved as a .dnx or .prj file and can be re-uploaded to other drives of the same variant.
9. To download a known-good parameter set, open Drive → Download to Drive. Select the source file and confirm. The drive writes the parameters and reboots into the new configuration.
10. Repeat for each drive on the bus, incrementing P780 between drives if using RS485 multi-drop.

DriveMonitor Version Compatibility and Software Behavior

DriveMonitor 5.2.x, 5.3.x, and 5.4.x all support the 6RA70. The differences that matter for the offline-state symptom are summarized below. DriverMonitor updates and downloads are distributed via the Siemens Industry Online Support portal.

If the COM port number is greater than 9 (typical with USB adapters), open Windows Device Manager, locate the adapter under Ports (COM & LPT), open Properties → Advanced, and remap the port to COM1, COM2, COM3, or COM4. DriveMonitor 5.x does not open COM10 and above reliably. The remapping is reversible and survives reboots.

Another known issue with DriveMonitor 5.2.1.1 in particular is the silent crash on start when the underlying Microsoft JET database engine is not present on Windows 10 / 11. Install the Microsoft Access Database Engine 2010 Redistributable (32-bit, even on a 64-bit OS) to resolve this. DriveMonitor is a 32-bit application and requires the 32-bit JET engine.

Multi-Drive USS Network Topology

For uploading parameters from more than one drive in a single session, switch the physical layer from RS232 to RS485 2-wire (the same X300 pin pair 3 and 7, with the drive jumpered into RS485 mode) or install PROFIBUS option modules. Each drive must then have a unique P780 address, and the bus must be terminated at both ends with 120 Ω between pins 3 and 7.

When commissioning a multi-drive line, change P780 on each drive before connecting DriveMonitor to the next. DriveMonitor's automatic scan returns the first drive that responds at the polled address; if two drives share an address, only the first responds and the rest remain invisible. Power-cycle the drive (24 V off / on) after each P780 change so the new address takes effect.

Related 6RA70 Fault Codes for USS and PROFIBUS

When USS communication is lost in operation, the 6RA70 reports one of the following fault codes on the PMU. Knowing these allows faster triage if DriveMonitor drops out mid-session.

Verification

Confirm successful online commissioning by checking the following:

• DriveMonitor's bottom status bar shows the connected drive firmware version (e.g. 1.8 / 5.4.2).
• The parameter tree opens and shows actual values (not dashes) for at least one parameter in each group.
• The PMU on the drive no longer displays a USS fault code (typically F027 / F028 on 6RA70 when the master has disconnected).
• A Drive → Upload to PG/PC operation completes without timeout and the resulting parameter file opens cleanly in DriveMonitor offline mode.
• A round-trip Download to Drive of the same parameter set returns no parameter-check errors in the bottom status bar.
• The r000 display on the PMU continues to show the drive state code (e.g. o7.0) without entering a fault state during the DriveMonitor session.

Troubleshooting Matrix

Frequently Asked Questions