Decoding Drive ES SIMO_MM4 Status Words and Resolving WinCC Faceplate Discrepancies in PCS 7

In SIMATIC PCS 7 utilizing Drive ES PCS 7 (DRVPCS7) and the SIMO_MM4 block for MICROMASTER 4 or SINAMICS drives, discrepancies between faceplate fault text and block icon graphics occur because the faceplate directly evaluates the drive status word (.Typical or STATUS), while the block icon graphics evaluate the WinCC alarm state (.EventState). To resolve this, decode the bitmask of the .Typical status word to identify drive-internal trips, and verify that drive fault telegrams correctly trigger the ALARM_8P message block.

Architecture of Drive ES SIMO_MM4 Status Processing

In SIMATIC PCS 7 installations controlling variable frequency drives (such as MICROMASTER 420/440 or SINAMICS G120/S120 with CU240E/CU250S), drives interface with the automation system via PROFIBUS-DP or PROFINET using standard telegrams (e.g., Telegram 1, Telegram 20, or Siemens Telegram 352). In classic PCS 7 projects, integration is executed using the Siemens Drive ES PCS 7 library (DRVPCS7) and the block SIMO_MM4 (FB50).

The SIMO_MM4 block performs cyclic cyclical communication with the drive over peripheral addresses (PPO types). It captures the 16-bit drive status word (ZSW1) and operating metrics (actual speed, motor current, torque) and formats this data for the Operator Station:
1. Cyclic Status Word (STATUS / .Typical): A WORD output containing packed binary flags reflecting the exact internal state of the drive inverter (Ready, Running, Faulted, Warning, Inhibit).
2. WinCC Alarm Generation (ALARM_8P): When an internal trip occurs, SIMO_MM4 passes trip bits to an embedded ALARM_8P call. WinCC evaluates this via the tag attribute .EventState, which drives the dynamic flashing icon (motor_error.emf).

When an operator observes that the WinCC faceplate indicates Fault, yet the motor block icon fails to display the red faulted graphic (motor_error.emf), a decoupling between the drive's cyclical status word and the asynchronous alarm logging queue has occurred.

Drive ES SIMO_MM4 Status Word (.Typical / STATUS) Bit Decoding Table

The .Typical (or STATUS in updated Drive ES releases) word maps directly to PROFIBUS ZSW1 drive status bits according to the following layout:

Bit PositionHex MaskPROFIBUS Status Definition (ZSW1)Faceplate Semantic MeaningMotor Block Icon ImpactBit 00x0001Ready to switch on (RdyOn)Drive precharged; ready for run commandGrey (Stopped)Bit 10x0002Ready to operate (RdyOp)DC bus charged; inverter enabledGrey (Stopped)Bit 20x0004Operation enabled (OpEn)Pulses enabled; motor runningGreen (Running)Bit 30x0008Fault present (Fault)Inverter tripped (overcurrent, thermal trip, etc.)Red (motor_error.emf via .EventState)Bit 40x0010Coast stop active (No OFF2)OFF2 command inverted (1 = Normal, 0 = Coast stop)Faceplate lockoutBit 50x0020Quick stop active (No OFF3)OFF3 command inverted (1 = Normal, 0 = Fast ramp)Faceplate lockoutBit 60x0040Switch-on inhibit (Lockout)Inverter restart locked; requires fault resetYellow Caution IconBit 70x0080Warning present (Warn)Non-tripping alarm (overtemperature warning)Yellow Flashing IconBit 80x0100Speed setpoint reached (SpdDev)Motor operating within tolerance band of setpointGreen (Running)Bit 90x0200Control requested (Local/Remote)PLC controls drive over bus (1 = PLC, 0 = Local panel)Remote indicatorBit 100x0400Comparison value reachedFrequency/current threshold attainedInformational

Distributor and hardware advisory: Confirm drive firmware compatibility and telegram configurations against official Siemens technical documentation.

Root Cause of Discrepancies: .Typical Status Word vs. .EventState

The discrepancy between faceplate text and block icon visualization stems from two distinct signal pathways:
1. Faceplate State Processing: The faceplate reads the live status word (.Typical) via WinCC tag polling. If Bit 3 (0x0008) is high, the faceplate script immediately prints the text Fault.
2. Block Icon Dynamic Bitmap Selection: Advanced status display objects (@PCS7Typicals) use .EventState to determine which .emf picture to render. .EventState is driven solely by the OS Alarm Logging server. If:
* The message call in SIMO_MM4 is suppressed via block input MSG_LOCK = 1,
* The message class in WinCC is disabled or filtered, or
* The message was acknowledged by another operator while the physical drive trip persists (Bit 3 remains high, but .EventState clears its unacknowledged alarm flag),
the faceplate will continue to read Bit 3 (Fault), while the icon reverts to grey or standard stopped representation because no unacknowledged alarm remains active in .EventState.

Step-by-Step Diagnostics and Telegram Alignment Procedure

To diagnose and synchronize the drive block status:

Monitor .Typical Word in CFC Online:
* Open the CFC chart containing the SIMO_MM4 instance.
* Switch CFC to Test > Watch On.
* Observe the hex value of output .Typical (or STATUS). Convert the hexadecimal value to binary to verify whether Bit 3 (0x0008) or Bit 6 (0x0040) is set.
Verify Drive Fault Codes:
* Inspect output FAULT_NO on SIMO_MM4. This integer reports the active drive fault code (e.g., F0001 Overcurrent, F0003 Undervoltage).
* Clear the drive fault by pulsing input RESET = 1 or commanding a reset from the faceplate.
Check MSG_LOCK and Alarm Configuration:
* Verify that input MSG_LOCK on SIMO_MM4 is 0. If MSG_LOCK = 1, all WinCC alarm generation is blocked, preventing .EventState updates.
* Right-click SIMO_MM4 in CFC, open Special Object Properties > Messages, and confirm that the alarm messages associated with signal 1 (Drive Fault) are properly compiled and active.

Verification

Verify consistent drive visualization:
1. Trigger a safe simulated drive fault (e.g., trip motor thermistor or trigger test fault F0001 via drive parameter P0004/P0947).
2. Confirm that the WinCC Alarm Logging list displays an active, incoming Drive Fault alarm.
3. Confirm that the motor block icon illuminates with motor_error.emf (flashing red).
4. Open the faceplate and verify that both the status text and the fault indicator display Fault.
5. Acknowledge the alarm in WinCC and reset the drive fault; verify that both the block icon and faceplate return to healthy operational states (grey stopped or green running).

Limitations and Operational Precautions

Never attempt to bypass drive hardware safety interlocks (such as Safe Torque Off - STO) using software reset commands on SIMO_MM4.
Drive ES PCS 7 is a classic library; when upgrading plants to PCS 7 V8.2 or V9.x, evaluate migrating from SIMO_MM4 to the SIMATIC PCS 7 Basis Library / Advanced Process Library (APL) with the Drive ES PCS 7 APL package (MotSpdCL interface).
Avoid modifying the internal mapping of .Typical bits in custom WinCC faceplates, as this will introduce incompatibilities with standard Drive ES upgrades.

Engineer FAQ

What is the difference between SIMO_MM4 in Drive ES and MotSpdCL in APL?

SIMO_MM4 is the legacy Drive ES block tailored specifically for MICROMASTER 4. MotSpdCL is the standard APL motor block with variable speed control, which interfaces with drives via the driver blocks PZD_In/Out or dedicated APL drive integration blocks.

Why does the drive faceplate show 'Switch-on Inhibit' (Lockout)?

Switch-on inhibit (Bit 6) indicates the drive cannot be started until a high-to-low transition occurs on the ON/OFF1 command, or a pending fault condition is cleared and acknowledged.

Can SIMO_MM4 communicate over PROFINET?

Yes, provided the drive is equipped with an appropriate PROFINET communication board (e.g., CBE20) and configured with compatible PPO or standard telegrams in HW Config.