Resolving APL_GS Drive Communication Errors (DatErr and ReqErr) After Mains Power Restoral in SIMATIC PCS 7

In SIMATIC PCS 7 v8.1 SP1 integrating SINAMICS G120 variable frequency drives via Drive ES PCS 7 APL blocks (APL_GS), a condition where mains grid power is lost (380VAC) while control electronics remain powered via 24VDC UPS will cause the APL_GS block to enter a latched Error state (DatErr = 1 and ReqErr = 1) upon mains power restoral. Even after drive alarms are acknowledged and the motor can accept run commands, the APL_GS error flags remain locked because the acyclic parameter communication channel (DPV1 / Dataset 47) detected a transmission abort during undervoltage. To resolve this without manual CFC intervention, engineers must configure SINAMICS automatic restart parameter p1210, implement an automated CFC pulse on the 'Restart' input upon fault clearance, or apply the latest Drive ES PCS 7 update.

Drive ES PCS 7 Communication Architecture (APL_GS and Cyclic Telegrams)

In SIMATIC PCS 7, integrating variable frequency drives into the Advanced Process Library (APL) environment utilizes the Drive ES PCS 7 library:
- APL_GS (or SINA_GS / MotSpdCL): The primary technological driver block interfacing the S7-400 CPU with SINAMICS G120 / S120 drives across PROFIBUS DP or PROFINET.
- Dual Communication Channels:
1. Cyclic Channel (PPO / Telegram 1, 20, 352): High-speed, deterministic exchange of Control Word 1 (STW1), Status Word 1 (ZSW1), Speed Setpoint (NSOLL_A), and Actual Speed (NIST_A).
2. Acyclic Channel (DPV1 Dataset 47): Asynchronous background reading and writing of drive internal parameters (e.g., fault memory r0945, motor current, thermal model states) handled by internal system function calls (SFB52 RDREC / SFB53 WRREC).

Mechanism of DatErr and ReqErr During Mains Power Interruptions

In Motor Control Centers (MCCs), a standard electrical topology utilizes 24VDC UPS backup for the drive Control Unit (CU240E/CU250S), while the 380V/480V 3-phase line feeding the Power Module (PM240) has no backup.

When a transient mains grid interruption occurs:
1. The Power Module loses DC link voltage, triggering drive fault F30003 (DC Link Undervoltage) or F07801 (Motor Overcurrent).
2. The Control Unit remains fully powered via 24VDC; cyclic fieldbus communication does not drop.
3. The APL_GS block initiates an acyclic read job (RDREC) to query the drive fault buffer.
4. Because the Power Module ASIC is unpowered, the drive returns an error telegram or times out.
5. APL_GS latches internal status bits:
- DatErr = 1 (Data communication error across acyclic channel).
- ReqErr = 1 (Job execution error).
6. When 380VAC power returns and the operator acknowledges alarms, the cyclic channel resumes normal operation (permitting motor run/stop), but the acyclic state machine remains locked in error until the Restart input pin is pulsed.

Why Acyclic Parameter Channels Lock While Cyclic Control Persists

Engineers are often confused why a drive can be started and stopped while APL_GS displays an active error state:
- Cyclic telegrams run in the high-speed I/O peripheral process image; as soon as the drive reports ZSW1.Bit0 = 1 (Ready to switch on), the controller can command the drive.
- Acyclic parameter jobs (RDREC) run in a state machine inside APL_GS. Once an acyclic job fails, the internal sequencer halts to prevent flooding the fieldbus with corrupt parameter requests. It strictly requires a re-initialization pulse on Restart to reset internal request buffers.

Solution 1: CFC Logic Automation for the Restart Input

Because the Restart input parameter is an internal configuration pin (attribute S7_link := false by default in some library releases), engineers can enable dynamic resetting via CFC:

Step 1: Make Restart Linkable in SCL / CFC

In SIMATIC Manager, open the Master Data Library block folder.
If Restart is not linkable, open block properties or SCL source and change attribute to { S7_link := 'true' }.
In CFC Editor, press F5 to update block types.

Step 2: Implement Auto-Reset Pulse Logic

Create a lightweight pulse generator triggered when:
- Drive Fault is cleared (Fault = FALSE).
- Mains voltage is restored (ZSW1.Bit0 = TRUE).
- Error bit is active (DatErr = TRUE OR ReqErr = TRUE).
Generate a single-cycle pulse ($100\text{ ms}$) connected to the Restart input pin.
Upon pulse arrival, APL_GS resets internal communication state machines; DatErr and ReqErr clear immediately.

Solution 2: SINAMICS Drive Parameter Optimization (p1210)

Configure the SINAMICS G120 drive firmware to handle power restoration autonomously:
1. In Siemens STARTER or via BOP-2 operator panel, configure:
- p1210 = 4 (Restart after line supply failure without additional start attempts).
- p1211 = 3 (Number of restart attempts).
- p1212 = 1.0 s (Delay time for restart).
2. With p1210 active, when 380VAC returns, the drive automatically clears the undervoltage fault and re-energizes its internal ASICs before APL_GS registers a communication timeout.

Diagnostic Matrix for Drive ES APL_GS Error Bits

The table below outlines diagnostic flags on the APL_GS block:

Output ParameterMeaningUnderlying ConditionCorrective ActionDatErr = 1Acyclic Data ErrorDPV1 parameter telegram timed out or abortedPulse Restart input; verify drive 24V/380V powerReqErr = 1Request Execution ErrorParameter job rejected by drive ASICAcknowledge drive fault; re-trigger parameter readGrErr = 1Group ErrorAny internal or drive fault activeCheck drive fault buffer in STARTER (r0945)ModErr = 1Module / Fieldbus FaultPROFIBUS/PROFINET cyclic communication lostCheck physical cable, connector, or switch

Verification

To confirm that drive communication recovery operates reliably:
1. Simulation of Grid Interruption: On the test bench or during cold commissioning, isolate the 380VAC main feeder to the MCC while maintaining 24VDC CU power.
2. Alarm Registration: Confirm that drive undervoltage alarm triggers and APL_GS logs the event.
3. Power Restoral Test: Re-energize 380VAC feeder; acknowledge alarms on the WinCC faceplate.
4. Autonomous Reset Audit: Confirm that DatErr and ReqErr clear automatically within 2 seconds without manual CFC intervention.

Limitations and Operational Precautions

Engineering teams must observe the following precautions:
- Automatic restart (p1210 > 1) must strictly adhere to plant personnel safety regulations; never configure automatic restart on drives driving hazardous exposed machinery without audible/visual start warnings.
- Continuous high-frequency pulsing of the Restart input can exhaust CPU communication buffers; ensure the reset pulse occurs strictly once upon fault restoral.
- Always validate final license quantities and MLFBs against the applicable Siemens catalog and authorized distributor quotation when ordering Drive ES PCS 7 software packages.

Engineer FAQ

What is the difference between Drive ES PCS 7 and standard APL MotSpdCL?

Standard APL MotSpdCL is a generic motor block that interfaces with channel driver Pcs7AnOu/Pcs7DiOu. Drive ES PCS 7 (APL_GS) is a specialized technological library providing direct acyclic parameter access, fault buffer decoding, and dedicated SINAMICS faceplates.

Does Drive ES PCS 7 require a separate engineering license?

Yes. Drive ES PCS 7 is a licensed add-on product requiring an engineering license in Automation License Manager on the Engineering Station.

Can APL_GS operate over PROFINET as well as PROFIBUS?

Yes. APL_GS supports both PROFIBUS DP and PROFINET IO communications using standard PROFIdrive telegram profiles.

Technical References

Related Tags

SINAMICS G120
Drive ES
APL_GS
DatErr
Power Failure

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Resolving APL_GS Drive Communication Errors (DatErr and ReqErr) After Mains Power Restoral in SIMATIC PCS 7