1. Overview
The Siemens MicroMaster 440 (MM440) frequency inverter accepts bidirectional run commands over its Profibus-DP option module through the process-data word STW1 (Control Word 1, word PZD1 from master → slave). Direction selection is implemented on bit 11 of STW1, regardless of whether the speed setpoint is positive or negative. This reference explains the cycle architecture, the exact bit map, the BICO interconnection required for the drive to honor the bit, and the verification steps that confirm correct field behavior on a PPO Type 1 cyclic channel.
The MM440 Profibus option is delivered as a removable module that occupies the front D-Sub port of the inverter. The drive is mapped into the PLC process image (PIW/PQW) according to the PPO type negotiated during DP slave initialization, and the control word is delivered as the first PZD word (PZD1). Bit 11 of that word is the standardized direction-reversal toggle for the PROFIdrive profile (PNO profile v3.1 / v4.0), and the MM440 honors it once the source for the direction reversal BICO parameter has been correctly linked.
2. PPO Type 1 Cyclic Frame Layout
PPO Type 1 is the most common cyclic frame for MM440 on Profibus-DP. It contains 4 words of parameter-channel (PKW) data plus 2 words of process data in each direction (PZD). The total telegram length is 8 words (16 bytes) per direction.
| Word | Master → Slave (PKW + PZD) | Slave → Master (PKW + PZD) |
|---|---|---|
| 0 | PKE — Parameter ID | PKE — Parameter ID |
| 1 | IND — Sub-index | IND — Sub-index |
| 2 | PWE — Parameter value (high word) | PWE — Parameter value (high word) |
| 3 | PWE — Parameter value (low word) | PWE — Parameter value (low word) |
| 4 | PZD1 — STW1 (Control Word 1) | PZD1 — ZSW1 (Status Word 1) |
| 5 | PZD2 — HSW (Main Setpoint, normalized speed ref.) | PZD2 — HIW (Actual Speed, normalized feedback) |
The PKW channel reads/writes any drive parameter (e.g., commissioning values or runtime monitoring). The two PZD words carry the cyclic real-time control: STW1 for commands and HSW for the speed reference (16-bit signed normalized to 0x4000 = 100% of reference frequency by default).
In Siemens STEP 7, PPO Type 1 maps as 4 input / 4 output words for the PKW section plus 2 input / 2 output words for the PZD section. The control word occupies QW of the PZD range starting at the configured I/O start address, e.g., QW 256 if the slave starts at byte 256.
3. STW1 Bit Map and the Role of Bit 11
STW1 is a 16-bit control word transmitted from the PLC (master) to the drive (slave) every bus cycle. The bits have specific functions defined by PROFIdrive and partially manufacturer-extended.
| Bit | Mnemonic | Function |
|---|---|---|
| 0 | ON/OFF1 | 1 = Run (with ramp), 0 = Stop (OFF1 ramp to 0) |
| 1 | OFF2 | 1 = enable, 0 = coast to stop (immediate pulse inhibit) |
| 2 | OFF3 | 1 = enable, 0 = quick stop (ramp P1135) |
| 3 | Enable pulse | 1 = inverter enable (pulse enable), 0 = inhibit |
| 4 | RFG enable | 1 = ramp function generator enabled |
| 5 | RFG start | 1 = unfreeze ramp output, 0 = freeze ramp at current value |
| 6 | Setpoint enable | 1 = release setpoint, 0 = inhibit setpoint (set 0) |
| 7 | Fault ACK | 0 → 1 rising edge acknowledges faults |
| 8 | JOG 1 | 1 = jog via fixed setpoint P1058 |
| 9 | JOG 2 | 1 = jog via fixed setpoint P1059 |
| 10 | Control from PLC | 1 = process data control active, 0 = local control |
| 11 | Direction reversal | 0 = forward, 1 = reverse (do not alter during ramp) |
| 12 | Reserved | 0 (drive ignores) |
| 13 | MOP up | Motorized potentiometer raise |
| 14 | MOP down | Motorized potentiometer lower |
| 15 | CDS bit 0 | Command data set select (0 = CDS0, 1 = CDS1) |
Bit 11 is the direction-reversal toggle. When the bit transitions from 0 → 1, the drive flips the rotating-field sequence applied to the motor, producing reverse rotation for any non-zero setpoint. Critically, the magnitude of the setpoint is unchanged — a positive HSW with bit 11 = 1 produces a negative rotating field. The bit must be stable before the setpoint is released (i.e., before bit 6 transitions to 1); changing it during a running ramp can trigger F0044 (counter-direction change during ramp) on MM440 firmware < 3.2.
4. Enabling Negative Setpoints vs. Using Bit 11
A common confusion arises from the difference between negative setpoint (HSW signed, e.g., -16384 dec = -100% of P2000) and direction reversal (bit 11 inversion with a positive setpoint). The MM440 supports both, but the parameter path differs.
4.1 Direction reversal via STW1 bit 11
This is the default behavior after Profibus quick commissioning. The BICO source for the direction-reversal parameter is wired to the received control word bit, so any toggle of bit 11 immediately reverses rotation direction. The speed setpoint remains an unsigned 0–100% value, and the drive applies the inversion internally.
4.2 True bipolar setpoint (negative HSW)
If you want to drive the motor with a signed 16-bit word where -16384 dec = full reverse and +16384 dec = full forward, you must change the setpoint source evaluation. The default reference frequency assignment uses P2000 as the normalization base; for bipolar operation the setpoint source connector must be scaled to allow negative inputs.
| Parameter | Default | Purpose | Bipolar setting |
|---|---|---|---|
| P0700 | 6 (COM link / Profibus) | Command source selection | Keep at 6 |
| P1000 | 6 (Profibus) | Frequency setpoint source selection | Keep at 6 |
| P1070[0] | r2050[1] (Profibus PZD2) | Main setpoint = received PZD2 | Keep at r2050[1] |
| P1075[0] | 0 | Supplementary setpoint | Leave at 0 unless additive control needed |
| P1113[0] | r2036.11 (control word bit 11) | BICO source: direction reversal | Keep at r2036.11 |
| P2000 | 50.00 Hz (motor-rated) | Reference frequency for normalization | Keep at motor rated |
If the requirement is purely "toggle direction with bit 11, send positive setpoint" — which is the simplest and most reliable configuration — leave the table above at defaults. To use negative HSW values, you must additionally route the signed setpoint via a BiCo-friendly connector. On MM440 firmware < 3.3, bipolar HSW requires parameter P2051 (sign-of-life / setpoint evaluation) and, in some builds, firmware-level normalization via P2021 (modbus/USS word order) and P2041 (Profibus PZD structure). On SINAMICS G120 the equivalent is P1070 = r2050[0] with normalization P2000 and P1155 = r2050[0] already enabling signed evaluation by default.
FB 30 / CTRL_VFD on STEP 7, or SINA_SPEED / SINA_FREQ blocks for TIA Portal) expects by default.5. Required Parameter Settings on the Drive
Below is the minimum parameter set after a Profibus quick commissioning (P0010 = 1) that ensures bit 11 is wired and honored. All values are entered with the BOP or via Starter / DriveMonitor / SINAMICS Startdrive.
| Parameter | Value | Meaning |
|---|---|---|
| P0010 | 0 | End commissioning |
| P0015 | 6 | Run macro: PPO Type with PKW+PZD2/2 (PROFIdrive) |
| P0700 | 6 | Command source = COM link (Profibus) |
| P1000 | 6 | Setpoint source = COM link |
| P1113[0] | r2036.11 | BICO source of direction reversal = received PZD1 bit 11 |
| P1120 | 10.00 s | Ramp-up time (set per mechanical need) |
| P1121 | 10.00 s | Ramp-down time |
| P1300 | 0 (V/f linear) or 20 (sensorless vector) | Control mode |
| P1500 | 0 | No torque setpoint via COM (speed mode only) |
| P2100[0] | r2036.7 (default) | Fault acknowledge via STW1 bit 7 |
Confirm P1113 is r2036.11 by reading P1113 in the parameter view — Starter will display it as a BiCo connector. If it has been overwritten during earlier commissioning, restore it. The connector r2036 is the decoded received PZD word 1 (STW1) by bit, so bit 11 of STW1 is r2036.11.
6. STEP 7 / TIA Portal Side: Building the Control Word
The control word is built as a 16-bit integer in the PLC and written to the process-output word corresponding to PZD1. The minimum pattern to enable forward run is shown below.
| Action | Bits | Hex | Decimal |
|---|---|---|---|
| Stop (all inhibit) | 0000 0000 0000 0000 | 0x0000 | 0 |
| Forward run, no enable yet | 0000 0101 0000 0110 | 0x0506 | 1286 |
| Forward run, full enable | 0000 0111 0001 1111 | 0x071F | 1823 |
| Reverse run, full enable | 0100 0111 0001 1111 | 0x471F | 18207 |
| Forward run, fault ACK edge | 1000 0111 0001 1111 | 0x871F | 34591 |
| OFF2 (coast) | bits 0,1,2,3 = 0,0,0,0 → 0000 0000 1101 1111 when running | 0x04DF | 1247 |
| OFF3 (quick stop) | bits 2=0 → 0000 0111 0001 1011 when running | 0x071B | 1819 |
Decomposition for the forward-run full-enable case (0x071F):
- Bit 0 (ON/OFF1) = 1
- Bit 1 (OFF2) = 1
- Bit 2 (OFF3) = 1
- Bit 3 (Enable pulse) = 1
- Bit 4 (RFG enable) = 1
- Bit 5 (RFG start) = 1
- Bit 6 (Setpoint enable) = 1
- Bit 7 (Fault ACK) = 0 (idle)
- Bit 8 (JOG 1) = 0
- Bit 9 (JOG 2) = 0
- Bit 10 (Control from PLC) = 1
- Bit 11 (Direction) = 0 → forward
For reverse, flip bit 11: 0x071F OR 0x0800 = 0x471F. A common implementation pattern in STEP 7 STL is:
// Build forward run command
L W#16#071F // base forward run pattern
// insert direction bit
L 'DB100.DBW2' // bForwardRun input from HMI (FALSE = 0)
==I // if forward, no override
SPB fwd
L W#16#071F
OW W#16#0800 // set bit 11 = 1 → reverse
T 'DB100.DBW4' // assembled STW1
SPA cmn
fwd: L W#16#071F
T 'DB100.DBW4'
cmn: NOP 0
In TIA Portal with the S7-1200 / S7-1500 and a GSD file for the MM440 (Siemens "DRIVE" GSD, file SI01810D.GSD or its successor), the standard block SINA_FREQ (FB 287 / FB 2870) assembles the control word internally. To enable reverse, pass the input SpeedSetpoint as a negative REAL value and leave bEnableReverse at TRUE. The block then sets bit 11 in STW1 automatically. This is the recommended path for new code.
7. Wiring Verification (Checklist)
After loading parameters and PLC code, walk through the following verification before energizing the motor:
- Confirm Profibus slave is in data exchange state (DP diagnostic LED on the option module is solid green, not flashing). On S7 hardware diagnostics, slave state =
0001(DX). - Read r2050[1] from the drive via the PKW channel. The value returned must match the STW1 word you are writing from the PLC. If it does not match, the cyclic mapping is offset or the PKW/PZD split is wrong.
- Read r2050[2] (PZD2 input word, the HSW you are sending). Verify it tracks your setpoint word in STEP 7 / TIA Portal online monitor.
- Confirm P1113[0] = r2036.11 via BOP or Starter. If it shows any other value, restore.
- Confirm P1500 = 0 so torque control is not interfering.
- Confirm P1300 matches the motor (V/f for simple pumps/fans, vector for high-dynamic loads).
- Send only the base forward pattern (0x071F) and a 0x4000 HSW (= +100% = P2000 Hz). Measure the actual frequency at the motor terminals with a handheld tach or read r0021 from the drive. It must read positive.
- Send the reverse pattern (0x471F) with the same HSW. The measured frequency must read negative. If it reads positive, P1113 has been inverted or P0748 wiring has accidentally redirected the bit.
- Toggle bit 11 while the drive is at zero speed (HSW = 0). It must switch direction without fault. If a fault occurs, log it via r0947 and r0949 and look up the number in MM440 fault list.
8. Status Word ZSW1 — What to Read Back
ZSW1 is the response from the drive, word PZD1 slave → master. The minimum useful bits for verifying direction control are:
| Bit | Function | Useful for |
|---|---|---|
| 0 | Ready to switch on | Confirms drive is initialized |
| 1 | Ready to operate | No fault, OFF1 = 0 |
| 2 | Operation enabled | Pulse enable set, motor is energized |
| 3 | Fault present | 0 = no fault, 1 = fault active |
| 4 | OFF2 inactive | Coast-stop not requested |
| 5 | OFF3 inactive | Quick-stop not requested |
| 6 | Switch-on inhibit | Drive is in inhibit state, ON command blocked |
| 11 | Direction actual | 0 = forward, 1 = reverse (matches STW1 bit 11) |
| 14 | Torque limit active | May indicate overload if P1500 is non-zero |
The HMI should read ZSW1 bit 11 and display the actual rotation direction as confirmation. If the PLC is sending bit 11 = 1 and ZSW1 bit 11 = 0, there is a BICO miswiring or P1113 has not been saved to the active parameter set.
9. Troubleshooting Matrix
| Symptom | Likely cause | Diagnostic | Remedy |
|---|---|---|---|
| Motor never runs in reverse | P1113 not pointing at r2036.11 | Read P1113 via BOP | Set P1113[0] = r2036.11 and save (P0971 = 1) |
| Reverse only at zero speed | F0044 counter-direction during ramp | Read r0947 | Pre-position bit 11 before setpoint release; update firmware |
| Drive trips F0001 overcurrent in reverse | V/f boost or ramp too aggressive | Check P1310, P1311, P1120, P1121 | Increase ramp time, reduce boost |
| Direction bit ignored, motor holds direction | Setpoint source not on COM (P1000 ≠ 6) | Read P1000 | Set P1000 = 6 (Profibus) and re-commission |
| Bit 11 toggles but HSW value is wrong | PKW/PZD offset mismatch | Compare r2050[1] with PLC output word | Re-check HW config PPO slot assignment |
| Speed sign flips independently of bit 11 | P1500 ≠ 0 torque override active | Read P1500 | Set P1500 = 0 unless torque-mode required |
| Profibus slave goes offline in reverse | Cable noise / missing termination | Check DP diagnostic: bus fault counter r2033 | Enable terminating resistors on both ends of segment |
| ZSW1 bit 11 always 0 | Drive in inhibit, ZSW1 stale | Check ZSW1 bits 0,1,2 | Resolve inhibit before reading direction feedback |
10. Related Drive Parameters Worth Knowing
- P1110 — inhibit negative direction (0 = allow reverse, 1 = block). If reverse is forbidden, set this to 0 first.
- P1111 — inhibit positive direction (reverse-only mode).
- P1130–P1134 — ramp smoothing curves. Set to 0 s if you want immediate direction transition at low speed.
- P1135 — OFF3 quick-stop ramp time.
- P0748.0 — invert digital output 1 (DSO). Accidentally inverting the direction in this parameter corrupts the bit semantically.
-
r2036 — received PZD1 word with bit-level access. Each bit is a BICO source:
r2036.0throughr2036.15. -
r2050 — received PZD array.
r2050[0]= PZD1 (STW1),r2050[1]= PZD2 (HSW). - r0021 — actual output frequency in Hz, signed (negative = reverse rotation).
- r0022 — actual motor speed in RPM, signed.
- r0947 / r0949 — last fault code and fault value.
11. Migration Note: MicroMaster 440 → SINAMICS G120
If a re-installation or replacement project brings the SINAMICS G120 with a CU240E-2 or CU250S-2 to the same Profibus network, the bit map and PPO layout are identical. The corresponding BICO wiring for direction reversal is on the G120:
- Command source:
p0700 = 6 - Setpoint source:
p1000 = 6 - Direction reversal BICO source:
p1113 = r2090.11(note: G120 uses the decoded control word at r2090, not r2036) - Setpoint input:
p1070 = r2050[1]
Reusing existing STEP 7 / TIA code is direct; the only change is the GSD file. Standard blocks SINA_SPEED (for closed-loop speed) and SINA_FREQ (for open-loop V/f) abstract the bit-pattern assembly.
12. FAQ
Which bit in STW1 selects the running direction on a MicroMaster 440 over Profibus?
Bit 11 of STW1. Setting bit 11 = 0 runs the motor in the forward direction; setting bit 11 = 1 runs it in reverse. The bit must be wired through BICO parameter P1113[0] = r2036.11 to be honored by the drive.
Do I also need to enable negative speed setpoints in the drive parameters?
Not if you are using bit 11 + an unsigned 0–100% HSW — that is the standard, default MM440 behavior after Profibus quick commissioning. You only need to re-evaluate the setpoint channel if you want to send a signed 16-bit word where negative values mean reverse speed; that requires additional BICO plumbing (P1070 / P1155) and is more common on SINAMICS G120 than on legacy MM440.
The MM440 ignores the direction toggle and runs only forward — what should I check first?
Read parameter P1113[0] on the BOP. If it does not show r2036.11, restore it, save with P0971 = 1, and power-cycle. Also confirm P0700 = 6 (command source = Profibus) and P1110 = 0 (negative direction allowed).
What is the standard forward-run control-word value to send from STEP 7 to a PPO Type 1 MM440?
W#16#047E (binary 0000 0100 0111 1110) is the often-cited "enable, no ON" pattern; W#16#047F (binary 0000 0100 0111 1111) is the equivalent with bit 0 = ON/OFF1 active. To run in reverse, OR in bit 11: W#16#0C7F. Always verify the exact word with online monitoring of r2050[0] on the drive.
Can I read back the actual rotation direction from the drive?
Yes — bit 11 of ZSW1 (Status Word 1, PZD1 from slave → master) returns the actual direction. Alternatively, parameter r0021 shows the signed actual output frequency in Hz and r0022 shows the signed actual speed in RPM.
Does bit 11 work if I am using USS instead of Profibus on the MM440?
Yes. The bit semantics are identical because the MM440 internally presents the same control word structure to the application. Whether the control word arrives via the Profibus option module (decoded into r2036) or via USS on the RS485 terminals (decoded into r2018), the BICO source for P1113 must be adjusted to the appropriate connector: r2036.11 for Profibus, r2018.11 for USS.