Cyclic and Acyclic Data Exchange Architecture Between SIMATIC PCS 7 and SIMOCODE pro

In SIMATIC PCS 7, communication with SIMOCODE pro motor management systems utilizes two parallel communication channels across PROFIBUS DP or PROFINET: cyclic process data exchange and acyclic data record transfers. Cyclic communication transfers time-critical control commands and status words via the CPU Process Image (Basic Type 1 or Basic Type 2), providing sub-second motor start/stop commands, trip states, and operating currents. Acyclic communication utilizes S7 system function blocks (SFB52 RDREC / SFB53 WRREC) to transfer non-time-critical diagnostic records (DS 92, DS 94, DS 130) on demand, enabling WinCC faceplates to display operating hours, thermal load curves, phase currents, and detailed trip histories via the SIMOCODE pro PCS 7 Library.

Dual-Channel Communication Architecture: Cyclic I/O vs Acyclic Records

In enterprise PCS 7 architectures, smart motor management relays (such as SIMOCODE pro C, pro S, and pro V) protect and control low-voltage motors in Motor Control Centers (MCC). To avoid overloading fieldbus bandwidth while ensuring deterministic control, Siemens decouples motor data into two distinct communication streams:

Communication StreamProtocol MechanismExecution FrequencyData ContentSystem HandlersCyclic Process DataHigh-speed Process Image (%I, %Q)Every controller cycle (OB35 100 ms)Start, Stop, Fault Reset, Run status, % CurrentChannel drivers (Pcs7DiIn, MMDIR)Acyclic Data RecordsDPV1 / PROFINET acyclic calls (RDREC)Asynchronous / On-demandEnergy (kWh), Phase currents (L1/L2/L3), Trip logsDiagnostic block MMDIAG / WinCC Faceplate

This separation guarantees that vital protection trips and interlocks execute deterministically, while rich maintenance datasets are retrieved in the background.

Cyclic Process Image Mapping: Basic Type 1 vs Basic Type 2

In HW Config, when configuring a SIMOCODE pro station on PROFIBUS DP or PROFINET, the engineer selects a standardized Basic Type defining the cyclic I/O structure:

Basic Type 1 (4 Bytes Input / 4 Bytes Output):
Inputs: Byte 0–1 = Status Word (Ready, Run Fwd, Run Rev, Tripped, Local/Remote). Byte 2–3 = Current $I_{act}$ (0 to 1000% of $I_s$).
Outputs: Byte 0–1 = Control Word (Start Fwd, Start Rev, Stop, Reset, Emergency Start). Byte 2–3 = Analog Setpoint / Reserved.
Basic Type 2 (16 Bytes Input / 4 Bytes Output):
Inputs: Expands input bandwidth to report total active power (Bytes 4–5), motor temperature (Bytes 6–7), energy metering (Bytes 8–11), and detailed status registers.
Outputs: 4 bytes of cyclic control commands.

For standard motor control, Basic Type 1 provides optimal bus efficiency and minimal cycle overhead.

Acyclic Data Records and the SIMOCODE pro PCS 7 Library Blocks

To eliminate manual communication programming, Siemens provides the dedicated SIMOCODE pro PCS 7 Library (APL-based). The library deploys specialized block instances in CFC:

MMDIAG (Hardware Diagnostic Driver): Placed automatically by the Driver Generator in @ system charts. It monitors the hardware address, handles acyclic reading of diagnostic records (Data Record 92), and issues system alarms.
Technological Control Blocks:
- MMDIR: Direct starter (single direction).
- MMREV: Reversing starter.
- MMSPD: Two-speed pole-changing starter.
- MMMEAS: Advanced measurement processing block.

When an operator opens the SIMOCODE faceplate in WinCC and switches to the 'Maintenance' or 'Measurement' view, MMMEAS issues acyclic RDREC calls to read Data Record 94 (measured values) and Data Record 130 (statistical data), populating phase current bars and thermal overload curves without consuming cyclic I/O bytes.

Verification

Confirm SIMOCODE communication and data integrity through these diagnostic procedures:

HW Config Online Status: In HW Config, select PLC -> Open Online. Confirm that the SIMOCODE pro station displays normal green status with zero PROFIBUS DP / PROFINET bus fault icons.
CFC Cyclic Signal Check: Switch CFC to Test Mode. Verify that MMDIR.CurRaw reads the expected percentage of full-load current when the motor is running.
WinCC Faceplate Diagnostic Read: In WinCC OS Runtime, click the motor icon. Open the SIMOCODE maintenance view. Confirm that operating hours, total start count, and phase currents (L1, L2, L3) populate within 1 to 2 seconds.

Limitations and Operational Precautions

When designing SIMOCODE pro networks in SIMATIC PCS 7, observe these engineering guardrails:

Library Version Uniformity: SIMOCODE PCS 7 Library versions must align with the PCS 7 host version (e.g. SIMOCODE Library V8.2 for PCS 7 V8.2). Never mix legacy non-APL SIMOCODE blocks with modern APL libraries.
Acyclic Call Throttling: Acyclic read requests (SFB52) are managed by internal CPU communication buffers. Do not call high-frequency acyclic blocks cyclically in fast OBs (e.g. OB32); run diagnostic reading on change or on-demand to prevent CPU buffer overflows.
Commercial Accuracy Notice: The SIMOCODE pro PCS 7 Library requires dedicated engineering and runtime licenses (e.g., 3ZS1632-1XX02-0YA0). Operating SIMOCODE blocks without valid ALM licenses causes engineering license deficiency warnings.

Engineer FAQ

Can I control a SIMOCODE motor without the SIMOCODE pro PCS 7 Library?

Yes. You can configure SIMOCODE as a standard DP slave, map its cyclic words to standard APL blocks (MotL) via channel drivers, and execute basic start/stop. However, you will lose the specialized WinCC faceplates, trip logs, and phase measurement views.

How is motor current scaled in cyclic communication?

In Basic Type 1, current is transmitted as a 16-bit integer representing percentage of set current ($I_s$) multiplied by 10. For example, a raw integer reading of 1000 corresponds to exactly 100.0% of rated motor current.