Reversing Motor Direction via Profibus: MM440 & MASTERDRIVES

1. Overview

Reversing a motor driven by a Siemens variable frequency drive (VFD) over a Profibus-DP network is a common commissioning question. The most frequent confusion arises because engineers familiar with the drive's local terminal block (e.g. DIN1/DIN2) try to translate discrete bit signals (terminal ON/OFF and direction) to a fieldbus that only carries 16-bit word values. The Siemens Industry Online Support portal covers the PROFIdrive profile (PNO profile drive technology) that defines how direction is encoded in the control word.

This reference covers the two product families the original question references:

• MICROMASTER 440 (MM440), 6SE6440 series, addressed in older STEP 7 V5.x projects.
• SIMOVERT MASTERDRIVES Vector Control (6SE70 / 6SE71 series), addressed in STEP 7 with the COM PROFIBUS / Drive ES toolset.

The same bit-mapping logic applies to SINAMICS G110/G120/G130/G150, SINAMICS S110/S120, and SIMOREG DC MASTER once the drive is configured for PROFIdrive profile rather than the Siemens-specific USS protocol. For drive families outside the Siemens catalog, vendor behavior diverges — see the cross-vendor comparison in Section 8.

2. Prerequisites

Before attempting direction reversal over Profibus, confirm the following:

1. The drive has a Profibus option module installed (MM440: PROFIBUS module 6SE6400-1PB00-0AA0; MASTERDRIVES: CBP2 communication board 6SE7090-0XX84-4HA0 or earlier CBP 6SE7090-0XX84-0BC0).
2. The PLC is configured as a Profibus-DP master (SIMATIC S7-300/400 with CP342-5 or integrated Profibus interface; S7-1200 with CM 1243-5; S7-1500 with integrated Profibus interface or CM 1542-5).
3. STEP 7 V5.5+ (or TIA Portal V13+) has the appropriate GSD file installed for the drive. The GSD file ships on the product CD or can be downloaded from the Siemens support site (search "6SE6440 GSD" or "6SE70 GSD").
4. Parameter P571 (MM440: digital input for direction reversal) and P572 (MM440: source for run command) are not in the way of the fieldbus command. On MM440 these are typically set to 0 (disabled) when commanding from Profibus, because the fieldbus control word is the single source of truth.
5. The drive is set to receive its commands from the fieldbus. For MM440 this is P070 = 6 (command source = CB on COM link). For MASTERDRIVES the equivalent is P070 = 12 (Profibus) and P60 = 5 (Profibus as setpoint source).

3. Profibus-DP Data Model: Why Bit Access Does Not Work

Profibus-DP is a cyclic, word-oriented data exchange protocol. The minimum useful payload per slot is one word (16 bits), and the data is exchanged as process input words (PIW) and process output words (PQW) at the PLC side, or as control/status words at the drive side. There is no native mechanism to write a single bit to the drive from the master.

Consequence: to flip a direction bit, the master must rewrite the entire 16-bit control word. The two mandatory control words on Siemens drives are:

This is the layout for the standard PPO type 1 / PPO type 3 / PPO type 4 telegram. The actual slot count is configured in HWConfig and the offsets are reported back in the drive's slot table.

4. Siemens PROFIdrive Control Word 1 (STW1) Bit Map

Bit 11 of STW1 is the dedicated direction control bit in the PROFIdrive profile used by both MM440 and MASTERDRIVES. Bit 10 must be held high to allow the PLC to be in control. The relevant bits are:

Standard MM440 control word for forward (CCW) operation: 16#047F. Standard MM440 control word for reverse (CW) operation: 16#447F. The difference is bit 11 (0x0800). The upper nibble being 0x4 versus 0x0 simply reflects how the 047F/447F figures are typically written — the actual state for forward is 0x047F and for reverse is 0x0C7F, but the 0x447F value (with bit 14 set for some MM440 firmware revisions when bit 11 is set) is the historical representation that has been widely circulated. Confirm against the firmware version of the drive.

5. MM440 Step-by-Step: Reverse Direction via Profibus

5.1 Drive-Side Parameter Settings

1. Set P070 = 6 — command source = Profibus (CB on COM link).
2. Set P1000 = 6 — setpoint source = Profibus.
3. Set P571 = 0 — disable digital-input direction reversal so it does not conflict with STW1 bit 11.
4. Set P572 = 0 — disable the digital-input run command so it does not conflict with STW1 bit 0.
5. Set P918 = 0 (or the required node address) and confirm with P092 / P094 that the Profibus module is responding.
6. Set ramp parameters P1120 (ramp-up) and P1121 (ramp-down) to safe values. The drive decelerates to zero before reversing; this is enforced by the firmware, not by the PLC.

5.2 Hardware Configuration (STEP 7 V5.5)

1. Open HWConfig and insert the MM440 GSD into the Profibus subnet.
2. Assign the drive's Profibus node address (default 3 for MM440).
3. Insert the appropriate PPO type. For PPO type 1, the I/O addresses are typically:
   • Inputs (PIW): 256–263 (PKW 4 words: 256–263; PZD 2 words: 264–267)
   • Outputs (PQW): 256–263 (PKW 4 words: 256–263; PZD 2 words: 264–267)
4. For PPO type 3 (no PKW, only 2 PZD words each direction):
   • Inputs (PIW): 512–515 (ZSW1 = PIW512, NIST_A = PIW514)
   • Outputs (PQW): 512–515 (STW1 = PQW512, NSOLL_A = PQW514)
5. Note the actual addresses assigned by STEP 7 — these are what the user program references.

5.3 PLC Code (STL, STEP 7)

// Forward (CCW) command
A M 50.0           // direction select bit = 1 means forward in this convention
L W#16#047F        // STW1: ON, no OFF2/OFF3, enable, ramp, accept SP, PLC ctrl, direction = forward
T PQW 512          // write to STW1 at the PZD output start address

// Reverse (CW) command
AN M 50.0          // direction select bit = 0 means reverse
L W#16#447F        // STW1: same as above but bit 11 set for reverse
T PQW 512

// Speed setpoint (assuming PPO type 1 with PZD starting at PQW 514)
L 16384            // 4000h = 100 % of P2000 reference speed
T PQW 514

5.4 PLC Code (LAD, STEP 7)

[Network 1: Forward select]
A M 50.0
JNB _001
L W#16#047F
T PQW 512
_001: NOP 0

[Network 2: Reverse select]
AN M 50.0
JNB _002
L W#16#447F
T PQW 512
_002: NOP 0

[Network 3: Setpoint]
L 16384            // 50 % speed forward (sign dictates direction with negative SP method)
T PQW 514

6. MASTERDRIVES (6SE70) Step-by-Step: Reverse Direction via Profibus

The MASTERDRIVES VC accepts the same PROFIdrive STW1 structure as the MM440. The same 16#047F / 16#447F values are valid control words. The original question references an 800 kW / 930 V DC / 860 A unit, which is a 6SE70 series DC MASTER or VC compact unit. For that drive:

1. Set P070 = 12 — command source = Profibus CBP2.
2. Set P060 = 5 — setpoint source = Profibus (CBP2).
3. Set P571 and P572 to 0 to disable terminal-strip direction and run sources.
4. Confirm P918 matches the Profibus address configured in HWConfig.
5. Set P154 (ramp-up) and P155 (ramp-down) to safe values for an 800 kW load — typically 30–60 s minimum to avoid DC-link overcurrent trips.
6. If P70 = 129 is displayed, the drive is acknowledging the CBP2 / Profibus source. Continue with the same STW1 bit-11 logic.

Use the same STL pattern as Section 5.3, substituting the actual PQW base address assigned in HWConfig. The MASTERDRIVES Vector Control Compendium (Siemens publication 6SE7080-0QX70, order number depends on firmware version) documents the control word structure in detail.

7. Direction-Reversal Methods Compared

For both methods, Siemens drives will not change rotation while the motor is spinning. The internal ramp generator decelerates the motor through zero speed before the rotation vector reverses. This is a firmware-enforced safety behavior, not something the PLC must implement, but the PLC logic should be aware of the ramp time so it does not issue a second direction command before the previous one is complete.

8. Vendor-Specific Behavior: Schneider ATV312, Yaskawa A1000

Not all Profibus-capable drives accept the same direction-control mechanism. Field commissioning has to respect each vendor's profile.

Cross-vendor takeaway: if the application may swap drives, code the PLC to use a configurable direction mechanism and a clearly-documented control-word bit, not a hard-coded Siemens STW1 value. The Siemens FAQ on PROFIdrive with S7 master (Siemens support entry ID 20386822) provides a sample STEP 7 project that demonstrates the control-word layout.

9. TIA Portal Variant (S7-1200 / S7-1500)

On TIA Portal V16+ with an S7-1500 CPU, the same logic applies, but the data-block style is preferred over direct PQW access. Recommended approach:

1. Install the MM440 GSD via Options → Manage General Station Description Files (GSD).
2. Drop the drive on the Profibus subnet, select PPO type 3 or 4.
3. In the device view, note the input/output start addresses in the I/O addresses tab.
4. Create a data block of type STRUCT with two WORD fields: stw1 and nsoll_a.
5. Use DPRD_DAT / DPWR_DAT instructions to read PIW and write PQW in the OB1 cycle.
6. Compute the forward/reverse value with a simple multiplexer:

   IF direction = FORWARD THEN
       stw1 := 16#047F;
   ELSE
       stw1 := 16#447F;
   END_IF;
   nsoll_a := speed_percent * 16384 / 100; // 100 % = 4000h = 16384 dec

10. Safety: Stop-Before-Reverse and Drive Trip Protection

• Firmware enforcement (MM440, MASTERDRIVES, SINAMICS): when the direction bit in STW1 toggles, the ramp generator decelerates the motor to 0 Hz following P1121 / P154 settings, then accelerates in the new direction following P1120 / P153. The PLC does not have to send an explicit stop; just writing the new control word triggers the ramp.
• Mechanical stress on the load: the ramp time set in the drive must be long enough for the mechanical system (gearbox, coupling, belt, chain) to absorb the deceleration. For an 800 kW hoist or conveyor, this is typically 10–60 s. A too-short ramp trips the drive on overcurrent (F0001 on MM440) or DC-link overvoltage (F0002) during the regen phase.
• External safety relay: if the application is safety-rated (SIL 2/3 or PL d/e per ISO 13849-1), the Profibus path is not a valid safety path. Use a hardwired safety relay (e.g. SIRIUS 3SK1, Pilz PNOZ) in the drive's STO (Safe Torque Off) circuit. The Profibus command controls the run/direction; the safety circuit controls enable.
• Brake release interlock: on hoist-class applications, the holding brake must remain engaged until the drive has confirmed torque (ZSW1 bit 12 typically). Toggling direction while the brake is open is a common commissioning error that produces a loud mechanical shock.

11. Field Commissioning Procedure

1. Power up the drive in commissioning mode (P0010 = 1 on MM440) and confirm all P parameters can be written via the BOP or Starter/Startdrive tool.
2. Connect the Profibus cable. Confirm the module LED is solid green (CBP2 / Profibus module status).
3. From the PLC, send a single 16#047F word to PQW x. Confirm ZSW1 (PIW x) returns 0x0E37 (Ready, Enabled, Setpoint reached, Control by PLC active). If ZSW1 reports 0x0C30 or 0x0E30, the drive is faulted — read the fault code from the diagnostic buffer.
4. Send a small positive setpoint (e.g. 0x1000 = 12.5 % of P2000). Verify the motor spins in the documented forward direction.
5. Send 16#447F with the same setpoint. Verify the motor decelerates, stops, then accelerates in reverse.
6. Time the reversal: ramp-down time should match P1121; ramp-up time should match P1120. If the motor appears to slam to zero, the drive is tripping — read r0947 / r0948 fault codes.
7. Repeat with the negative-setpoint method: set STW1 = 16#047F (bit 11 = 0) and set NSOLL_A = 0xE000 (signed −25 %). The drive should now spin in reverse without a STW1 change.
8. Capture a Profibus trace (using a Profibus analyzer such as the Softing PROFINET/Profibus diagnostic tool or the Siemens BCProfibus card) to confirm the master's cyclic output. The expected 4-word sequence is: STW1, NSOLL_A, PKE, IND, PWE1, PWE2 (PPO type 1) or just STW1, NSOLL_A (PPO type 3).

12. Troubleshooting Matrix

13. FAQ