Micromaster 4 Parameter Restore: Fix MM440 Profibus Address Failure

When an engineer replaces a Siemens MICROMASTER 4 (MM4) drive family member (MM420, MM430, or MM440) and uploads a parameter set captured with STARTER commissioning software, the field bus address sometimes fails to apply. The drive powers up on the default Profibus node, the PLC reports a missing slave, the Profibus module LED turns amber, and the bus fault (BF) LED on the S7 CPU lights red. This article documents the root cause, the parameter interactions that trigger the fault, and the exact recovery procedure for MM440 drives equipped with the Profibus Communications Module.

1. Problem Details

The reported symptom is reproducible across the MM4 family when the backup/restore cycle is performed with command and setpoint sources temporarily redirected to a non-field-bus source. The exact sequence observed by a typical field engineer is as follows:

1. The original MM440 is in service with a Profibus Communications Module installed on the front of the drive (e.g., 6SE6400-1PB00-0AA0).
2. The engineer launches STARTER, sets P0700 = 4 (command source = serial interface / STARTER), sets P1000 = 4 (setpoint source = serial interface / STARTER), and sets P2010 = 6 (USS baud rate, when needed for the serial commissioning cable), then performs an Upload to PG/PC to capture all parameters.
3. The original drive is removed and a new (factory-default) MM440 with the Profibus module installed is mounted and wired identically.
4. STARTER performs a Download to Target Device with the saved parameter set, the engineer restores P0700 = 6 and P1000 = 6 (Profibus control), powers the drive, and observes that the bus address reported by the drive does not match the backed-up value.
5. The PLC reports the expected node (for example node 11) as missing. The Profibus module BF LED is red. The drive's BOP/AOP keypad shows the field-bus address as 3, not 11.
6. Manual entry of the correct address on the BOP (or via STARTER) restores Profibus communication and normal operation.

2. Affected Products and Firmware

The MM4 product family addressed by this article is:

The behaviour described is present in all MM4 firmware versions that implement the standard parameter set defined by the Parameter List manual. The fault is independent of firmware version but is more likely to be encountered on firmware versions below V3.20 because the legacy default field-bus address (3) is consistent across the family. A field firmware upgrade using STARTER should not be attempted to resolve this issue; the address is a parameter-level concern, not a firmware-level concern.

3. Parameter Reference

MM4 parameter access is gated by an access level (r0003 / P0003) and a configuration level (r0007 / P0007). The following parameters are central to the backup/restore sequence and to field-bus commissioning. The values shown are the firmware defaults that apply at first power-up of a new MM440 drive.

4. Root Cause Analysis

Three mechanisms combine to produce the failure. Each one is independently correct; the failure arises because the engineer typically encounters two or three of them simultaneously during a hot-spare replacement.

4.1 P0700 / P1000 writes trigger a parameter reset

The single most important behaviour to understand is that a write to P0700 or P1000 on MM4 firmware is treated as a configuration change that requires the entire parameter set to be re-initialized for the new source. This is not a parameter-modify operation; it is closer to a factory-reset operation masked as a single write. The drive keeps parameters such as motor data (P0304, P0305, P0307, P0310, P0311, P0335) intact for safety reasons, but communication parameters such as P0918, P0922, P2040, P2041, and several P2000-series scaling factors are reset to source-dependent defaults. The Profibus node address defaults to 3.

The engineer in the source scenario performed the following sequence:

1. Set P0700 = 4 and P1000 = 4 on the original drive to enable STARTER download. This first write already resets P0918 to the value associated with the serial interface source — which, for the MM440 default firmware, is 3.
2. Captured the parameter set. At this point, the backup file contains P0918 = 3, not the original 11. The engineer reported that the backup contained the value 11, which would only be true if the write to P0700/P1000 occurred after the upload, or if the upload was performed via the access level path that does not pass through the source-change gate. The fault therefore manifests in one of two ways: (a) the address in the backup is the post-reset default and is uploaded correctly but as the wrong value, or (b) the address in the backup is correct, but the subsequent restore to P0700 = 6 re-initializes P0918 to the Profibus-source default of 3 after the restore.
3. Restored P0700 = 6 and P1000 = 6. This is the second reset trigger, and it is the most common cause of the symptom. The drive re-initializes Profibus-side parameters for the Profibus source and writes the Profibus default address (3) into P0918.

4.2 DIP switches override P0918 at power-up

The MM4 Profibus Communications Module is fitted with an 8-position DIP switch on the left edge of the module, accessible behind a small window or via removal of the terminal cover. The DIP switches are read by the module firmware only at power-up of the drive. If the binary value presented on the switches is non-zero, that value overrides the parameter P0918 for the duration of the current session. The override persists until the drive is power-cycled; a subsequent power-up will read the switches again and apply the override.

The least-significant bit is on the left side of the switch block. A switch in the OFF (down) position represents a 0; ON (up) represents a 1. The address presented on the switches is the binary value 1 + binary value as documented in the module manual, meaning an all-OFF setting produces address 0 in the switch read but does not force a zero address onto P0918 — instead, an all-OFF setting tells the module to honor P0918. Any other setting forces that value.

If a spare Profibus module is fitted to the replacement MM440 and the DIP switches were left at a non-zero factory test setting (commonly 3), the module will report address 3 regardless of any value stored in P0918. This is the second independent cause of the symptom and is the most frequently missed root cause in the field.

4.3 STARTER serial upload requires P0003 = 3

The parameter P0918 is an expert-level parameter and is not visible in the STARTER parameter list when the user access level P0003 is at the default 1 (Standard). The engineer must set P0003 = 3 (Expert) before the upload for the parameter to be captured. If the original upload was performed at P0003 = 1, the backup file simply does not contain P0918 and the restore cannot write it back. STARTER typically warns "Parameter P0918 not in project" but the warning is buried in the download dialog and is easy to miss.

5. Solution Procedure

The following procedure resolves the fault in all three root-cause cases. Execute the steps in order.

5.1 Confirm the parameter access level

1. Connect to the drive via STARTER (USB-to-RS485 PC converter, e.g., 6SE6400-1PC00-0AA0) or via the BOP/AOP keypad.
2. Set P0003 = 3 (Expert access level). Confirm by reading r0003; it must return 3.
3. Navigate to P0918. If the parameter is not visible, the Profibus Communications Module is either not fitted, not powered, or in fault. Check the module seating and the 24 V supply to the module's Profibus connector pins 6 and 5.

5.2 Clear the DIP-switch override

1. Remove the 24 V supply to the drive and to the Profibus module.
2. Open the Profibus module cover and inspect the 8-position DIP switch block.
3. Set all switches to OFF (down). This is the only configuration that allows P0918 to take effect at power-up.
4. Re-fit the cover and restore 24 V to the module.

5.3 Write the Profibus address directly

1. On the BOP, press P, then arrow up until P0918 is shown. Press P to enter edit mode.
2. Use the up/down arrows to reach the desired address (1–126). Press P to confirm.
3. Cycle drive power to apply the new address. The address shown on the BOP after the next power-up is the value the module will present on the wire.

Alternatively, in STARTER with expert access enabled, enter the address in the parameter list and click Download to Target Device. The change is applied without a power cycle on STARTER-driven writes, but a power cycle is still required if any other Profibus-side parameter is being changed concurrently.

5.4 Verify command and setpoint source

After the address is set, confirm that the drive accepts Profibus commands:

1. P0700 = 6 (Profibus command source).
2. P1000 = 6 (Profibus setpoint source).
3. P0922 = 1 (Standard Telegram 1) or the value required by the PLC program.
4. P2040 (process data monitoring time) — set to at least 200 ms to avoid nuisance faults from momentary telegram gaps during PLC restart.

6. STARTER Software Workflow for Backup and Restore

The correct sequence for capturing an MM4 parameter set for spare-part cloning differs from the casual sequence most engineers use. The following workflow avoids the P0918 issue by performing the upload before changing the command source.

6.1 Capture (from the running drive)

1. Open the existing STARTER project that matches the running drive, or create a new project and perform an Online → Accessible Nodes search.
2. Right-click the drive and select Online → Upload to PG/PC. STARTER reads every parameter that is visible at the current access level. Do not change P0700 or P1000 before this step.
3. After the upload, set P0003 = 3 and perform a second upload. This captures P0918 and other expert parameters.
4. Right-click the drive and select Save data to memory card or Export to a .dvg / .xml file. Save both the project backup and a flat parameter export.

6.2 Restore (to the spare drive)

1. Open the saved STARTER project. Confirm that the offline view shows P0918 with the correct value.
2. Connect to the replacement drive (factory default state, DIP switches all OFF on the Profibus module).
3. Set P0003 = 3 on the online drive before the download. This ensures the drive accepts P0918 as a writable target.
4. Right-click the drive and select Download to Target Device. In the dialog, select Copy RAM to ROM so the parameters survive a power cycle.
5. Confirm with the PLC that the slave is now visible.

7. Verification

After the restore and address fix, verify the system end-to-end with the following checks.

1. BOP address check: Power-cycle the drive, then read r0918 on the BOP. It must equal the desired node number.
2. PLC online check: In STEP 7 (or TIA Portal), open the hardware online view and confirm the drive is visible at the configured address with no diagnostic interrupt.
3. LED check: The Profibus module's green Online LED must be lit solid; the red BF (Bus Fault) LED must be off. The S7 CPU's BF LED must be off.
4. Control word check: Force control word 1 (STW1) to 0x047F (OFF1 = 0, OFF2 = 1, OFF3 = 1, Enable = 1) and read status word 1 (ZSW1) back. ZSW1 bit 2 ("Operation enabled") must clear and bit 6 ("Switch on inhibited") must set, confirming that the drive is responding to Profibus commands.
5. Fault buffer check: Read r0947[0..7] on the BOP. No active fault code should be present. If fault F0070 (no PZD communication from CB) or F0071 (USS timeout) is present, the PLC is not transmitting telegrams and the wiring or PLC program must be inspected independently.

8. Fault-Code Mapping

The following drive faults are commonly observed during or after the MM4 backup/restore sequence and indicate specific causes that should be ruled out before re-running the procedure.

9. Related Parameter Behaviour

The reset behaviour of P0700 and P1000 propagates into several other parameters that engineers often miss. After a restore, double-check the following values are at the expected site-specific values, not at the source-default:

• P0922 — Telegram selection. Default 1 (Standard Telegram 1). Sites using Telegram 3, 4, 9, or free PZD mapping (999) often find this reset to 1 after restore.
• P2040 — Process data monitoring time. Default 100 ms (MM440). Sites that have tuned this to 200–500 ms to ride through PLC restart transitions will see it reset to 100 ms and start faulting with F0070 after the next PLC restart.
• P2041 — Process data mapping. Default 0. Sites using free PZD mapping will see the drive revert to the fixed mapping of the selected telegram.
• P2051 / P2061 — PZD receive words for CB and BOP-link. Reset to defaults on source change.
• P2000 — Reference frequency. Default 50 Hz. Sites that have set 60 Hz will see this revert.
• P2002 — Reference current. Reset to the drive's rated current.

10. Best Practices for Spare-Drive Management

1. Pre-stage the spare: When a new MM440 arrives from the spares store, fit the Profibus module and set all DIP switches to OFF before the spare goes into the rack. This eliminates the DIP-switch override as a variable during emergency replacement.
2. Pre-load the spare: For critical assets, keep a "known-good" .dvg file on the engineering laptop and on a memory card (if the drive supports it). A pre-loaded spare can be deployed in minutes without an online commissioning session.
3. Document the access level: Add a label to the cabinet stating "MM4 access level: 3 (Expert)" so the next engineer does not need to guess.
4. Verify before power-up: After any restore, read r0918, r0922, r2040, and r0700 / r1000 on the BOP before issuing the first run command. The values must match the documentation.
5. Isolate the PLC handshake: With the drive in P0700 = 6, the PLC's first control word must be a safe state (e.g., 0x0000 or 0x047E) to prevent an unintended run when the bus comes up.
6. Use a checklist: The MM4 backup/restore sequence is a candidate for a one-page printed checklist: 1) verify access level, 2) capture upload, 3) capture expert upload, 4) verify DIP switches, 5) restore, 6) verify P0918, 7) power cycle, 8) verify bus LED, 9) verify ZSW1, 10) clear fault buffer.

11. Frequently Asked Questions