MM150 to MM440 Profibus Upgrade: Resolving Motor Run Fault

Problem Description

When a Siemens MICROMASTER 150 (MM150/3) inverter equipped with the legacy Profibus communications module 6SE3(9)290-0XX87-8PB0 is replaced by a MICROMASTER 440 (MM440) fitted with the current 6SE6400-1PB00-0AA0 Profibus module, the PLC establishes cyclic communication without bus faults and reports the slave as healthy. The same Profibus address, the same I/O mapping, and the same PPO3 telegram structure are reused, but the motor refuses to run. Drive status reports a missing "enable," the ramp generator remains locked, and no torque is developed even though the bus is exchanging process data with the master.

The fault is not a hardware failure and is not a Profibus diagnostic interrupt. It is a parameter, control-word, and watchdog mismatch between the older MM150 firmware interpretation of the PROFIdrive profile and the MM440 firmware interpretation. This article consolidates the field-verified root causes, the parameter corrections, and the verification procedure required to bring a swapped MM150 → MM440 installation to a running state without changing the master PLC program.

Hardware Migration Path

Both inverters accept the same screw-terminal Profibus connector (D-sub 9) and the same PROFIdrive PPO types, but the firmware generation is different. The MM150 predates the consolidated PROFIdrive V2.0 Class 1 implementation that is native to the MM440, and the control word/staus word bit semantics were tightened in the MM440 firmware.

When the new MM440 is dropped into a slot previously occupied by an MM150, the master continues to push the same PPO3 frame. The MM440 must be told to (a) accept command and setpoint from Profibus, (b) tolerate the master's PPO3 telegram layout, and (c) interpret the legacy control word correctly. Each of these is a parameter-driven action.

Root Cause Analysis

Three independent root causes commonly co-exist on a freshly installed MM440 that is not running. They must all be corrected before the drive will respond to the master.

Root Cause 1 — Watchdog default holds the drive in Com Loss state

Parameter P2041.00 in the MM440 (Profibus telegram timeout / fieldbus watchdog) is factory-defaulted to 0, which in the legacy MM150 meant "watchdog disabled." On the MM440 firmware used with the 6SE6400-1PB00-0AA0 module, a 0 value can be interpreted as "fault immediately on first cycle missed" rather than "watchdog off." SIEMENS technical support has confirmed that the value must be raised to 3 when PPO3 is used, which corresponds to a 30 ms tolerance window between Profibus cycles. With the watchdog at 0, the drive may trip F072 (communication loss) or, more subtly, refuse to leave the "not enabled" state even though no fault code is latched.

Root Cause 2 — Command and setpoint BICO source not set to Profibus

A factory-default MM440 uses the analog and digital terminals (P700 = 1, P1000 = 1). Without explicitly setting both to 6 (Profibus CB), the BICO matrix continues to drive the inverter from the terminals. Even if the PLC is pushing a perfect PPO3 frame, the control word is read into r2050[0] and the setpoint into r2050[1], but they are not wired into the inverter state machine. The motor simply sits idle because the inverter is not looking at the bus.

Root Cause 3 — Control word bit semantics differ between MM150 and MM440

The MM150 firmware mapped "setpoint inversion" to bit 14 of the control word. The MM440 firmware, conforming strictly to PROFIdrive V2.0, maps that same function to bit 11 (P1113: BI Setpoint inversion). If the master continues to send the MM150-shaped control word with bit 14 = 1, the MM440 will interpret it as a vendor-specific bit and may additionally enter "control by PLC" demotion if bit 10 is not asserted. Field observation: bit 0 and bit 1 of the read status word toggle rather than latch at 1, which prevents the inverter from reaching the Operation Enabled state (bit 2).

Required Parameter Settings

The table below lists the minimum MM440 parameters that must be set after a MM150 → MM440 swap. Defaults shown are the MM440 factory defaults; "Required" is the value needed for a PPO3-controlled application.

The BICO connections P2051.0 = 52 and P2051.1 = 21 tell the MM440 which inverter internal signals to publish back to the master in the two PZD receive words of the PPO3 reply. r0052 (Status word 1) and r0021 (Actual frequency) are the conventional choices and reproduce what the MM150 was returning.

PPO3 Telegram Structure

PPO3 is the parameter-process-data object with 0 PKW (parameter channel) words and 4 PZD words total — 2 PZD words from master to slave (receive) and 2 PZD words from slave to master (send). This is the smallest PROFIdrive telegram that carries a control word, a setpoint, a status word, and an actual value, and is therefore the common choice for legacy MM150 replacements.

The receive words land in r2050[0] (control) and r2050[1] (setpoint). The send words are sourced from the parameters wired into P2051.0 and P2051.1 respectively. The PLC programmer should confirm via the master diagnostic buffer that the first two PZD words are the control word and the frequency setpoint in that order, and that the reply's first two PZD words are the status word and the actual frequency.

Control Word Bit-by-Bit Comparison (MM150 vs MM440)

Status Word Bit-by-Bit Comparison (MM150 vs MM440)

The state machine that the master must respect is:

1. Status word bit 6 = 1 (switching on inhibited) — clear by toggling control word bit 0 from 1 → 0 → 1.
2. Status word bit 0 = 1 (ready to switch on) — main contactor closes, DC bus charges.
3. Status word bit 1 = 1 (ready to operate) — drive waits for ON command.
4. Master raises control word bit 0 (ON/OFF1), bit 3 (enable), bit 4 (RFG enable), bit 5 (unfreeze), bit 6 (setpoint enable) all to 1.
5. Status word bit 2 = 1 (operation enabled) — motor starts to ramp.

If the master asserts bit 0 of the control word before status bit 0 has latched, the state machine bounces and the motor never reaches step 5. This is the most common cause of the "bit 0 and bit 1 swap, never together" symptom observed in the field.

Step-by-Step Commissioning Procedure

1. Mechanically install the MM440. Confirm the frame, the motor cable cross-section, and the PE grounding match the existing cabinet layout. Verify that the Profibus D-sub connector pinout (pin 3 = B-line, pin 8 = A-line) is preserved from the MM150 wiring.
2. Address the slave. Set the DIP switches on the 6SE6400-1PB00-0AA0 module to the address the MM150 used (e.g., 4, 7, 12, etc., 1–125). Alternatively, set the DIP switches to 0 and assign the address via P0918. Note: changing address requires a Profibus reset (power cycle of the bus or restart of the drive).
3. Power the drive and reset to factory. With the BOP or Starter connected, set P0010 = 30 and press P. The drive executes a factory reset (all user parameters return to defaults). Then set P0010 = 0.
4. Run quick commissioning. Set P0010 = 1. Enter motor nameplate values: P0304 (V), P0305 (A), P0307 (kW), P0310 (Hz), P0311 (rpm), P0335 (cooling). Set ramp times P1120 / P1121. Set control mode P1300 = 0 (V/f linear) to match the legacy MM150 application. Exit quick commissioning by setting P0010 = 0.
5. Set command and setpoint source to Profibus. Set P0700 = 6 and P1000 = 6. Save with P.
6. Set the Profibus watchdog. Set P2041.00 = 3 (3 telegram cycles of tolerance for PPO3). Optionally also raise P2040 = 50 ms as a cushion against single-cycle jitter.
7. Verify BICO source defaults. Read P0810 and P0811; both must be 0 (use the default r2050[0] path for the control word). If they are non-zero, set to 0 and save.
8. Verify PZD connections. Read P2051.0 = 52 and P2051.1 = 21 (or whatever the master expects). Adjust if the master reads current instead of frequency, etc.
9. Re-map the control word in the master. Change bit 14 of the master's control word to bit 11. Do this in the PLC program, not in the drive — the MM440 will not interpret bit 14.
10. Reset the master-side state machine. Issue a control word 0x0000 → 0x0400 (bit 10 = control by PLC) → wait for status 0x0210 (bits 0, 5, 8 = 1) → 0x0400 + 0x0001 = 0x0401 (ON/OFF1 + PLC control). Then watch the next status poll for 0x0231 (bits 0, 1, 4, 5, 8 = 1) and finally 0x0233 (bit 2 = operation enabled).

Online Verification and Diagnostics

Connect to the drive with STARTER or Starter Drive ES and read the following live parameters while the master is supposedly commanding RUN. If the drive is not yet online, the BOP can read most of these via r0000-class navigation.

If r2050[0] shows the expected control word but r0054 does not, the BICO path is broken: check P0810, P0811, and the inverter state machine. If r2050[0] is zero or stale, the watchdog has dropped the receive frame: re-check P2041.00 = 3 and P2040.

Troubleshooting Matrix

Field-Proven Notes and Caveats

• PPO3 vs PPO4: PPO3 carries 4 PZD total, PPO4 carries 10 PZD. The MM440 GSD file allows either. If the master was configured for PPO4 on the MM150, the MM440 will also accept it, but the watchdog timing in P2041.00 may need a different value (typically 5 for PPO4). Verify the GSD file revision loaded for the 6SE6400-1PB00-0AA0 against the PLC HW config; mixing GSD revisions is a common cause of "bus OK, drive does not respond."
• GSD file: Use the Siemens GSD for the 6SE6400-1PB00-0AA0 — file name typically SIEM8120.GSD or similar. Do not reuse the MM150 GSD; even though both inverters speak PROFIdrive, the GSD tells the master what PPO types and diagnostics the slave supports.
• Watchdog interpretation drift: The same parameter (P2041.00) has carried different semantics across MM440 firmware versions. On firmware V1.x it is a 0/1 enable. On firmware V2.x and V3.x it is a numeric tolerance in units of telegram cycles. Always confirm the parameter's behavior against the firmware version stamped on the drive's rating plate and consult the parameter list for that firmware.
• Setpoint scaling: The setpoint from the master in PPO3 PZD2 is normalized to P2000 (default 50.00 Hz). A value of 0x4000 (16384) = 100 % of P2000. If the application used a different reference on the MM150, set P2000 on the MM440 to match before the swap.
• Motor identification: For a no-fault first start, the MM440 should be allowed to run motor identification (P1910 = 1) on a no-load run. The legacy MM150 often did not require this; the MM440 will perform better with it.
• Brake control: If the application uses a holding brake, the MM440 routes the brake control through the relay output (P0731, P0732) or a digital output (P0748 family). The MM150 used a different convention. Check that the brake releases on RUN enable and reapplies on OFF1 ramp completion.
• EMC and grounding: The Profibus cable shield must be bonded to PE at both ends through the connector backshell. The MM440 EMC filter inside the drive is more sensitive to shield discontinuity than the older MM150; a missing shield bond will pass bus diagnostics but inject enough noise to corrupt the watchdog check.
• Failure mode after a hot swap: If a drive was swapped while the bus was live, the new MM440 will come up with the Profibus stack not initialized. Power-cycle the Profibus segment or issue a master-side bus restart to bring the new slave online without an F0072.

Frequently Asked Questions