C135 PCS 7 (PCS7)
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Integrating FM 350-2 Counter Modules in S7-400H Systems and Resolving FM_DATA Compilation Errors in PCS 7

Integrating FM 350-2 Counter Modules in S7-400H Systems and Resolving FM_DATA Compilation Errors in PCS 7

To resolve the CFC compilation error 'Parameter CFC(1).1.FM_DATA is not interconnected with a data source' when configuring the SIMATIC FM 350-2 counter module, create a dedicated data block using UDT1 (from the FM 350-2 setup library) in the S7 Program's Blocks folder, and interconnect this DB directly to the FM_DATA parameter of driver block CNT_CTL (or FM_CNT). In redundant S7-400H configurations with ET 200M distributed I/O, FM 350-2 function modules cannot be configured as redundant I/O pairs; they operate as single-channel modules in separate ET 200M racks, requiring software-level signal cross-checking in CFC. In Frequency Measurement mode, onboard digital outputs cannot execute direct hardware comparator gating and must be controlled via cyclic AS logic.

Table of Contents

Executive Summary

The SIMATIC FM 350-2 is an 8-channel intelligent counter and frequency measurement module utilized for high-speed pulse counting, flowmeter integration, and rotational velocity monitoring. When integrating the FM 350-2 into high-availability S7-400H systems via distributed ET 200M stations, engineers regularly encounter two major technical hurdles: first, attempting to pair two FM 350-2 modules under standard S7-400H redundant I/O wizard tools fails because function modules lack redundant firmware synchronization. Second, during initial CFC compilation, the driver block generates the critical error: 'Parameter CFC(1).1.FM_DATA is not interconnected with a data source'. Additionally, confusion exists regarding the operation of the module's digital outputs in frequency mode. This technical guide explains the architectural constraints and configuration steps.

FM 350-2 Functionality in SIMATIC PCS 7

The FM 350-2 module (6ES7350-2AH01-0AE0) operates with autonomous microprocessor intelligence:

  • Supports 8 counter channels up to 20 kHz (or 4 channels up to 100 kHz with 24V incremental encoders).
  • Executes operating modes: continuous counting, periodic counting, frequency measurement, speed measurement, and period measurement.
  • In PCS 7, communication is handled via channel driver block CNT_CTL (FB127) or FM_CNT (FB128), which transfers control commands and readback values asynchronously via SFC58/SFC59 (WR_REC / RD_REC).

S7-400H Redundant Architecture Constraints for Function Modules

In SIMATIC S7-400H fault-tolerant systems:

  • Standard digital and analog I/O modules (such as SM 321 or SM 331) support redundant paired configuration with automatic driver failover via Pcs7DiIn and Pcs7AnIn.
  • Function Modules (FM) and Communication Processors (CP) cannot be paired as redundant I/O in HW Config. The S7-400H system does not support automatic bumpless hardware state synchronization between two separate FM microprocessors.
  • To achieve measurement redundancy, engineers must install two separate FM 350-2 modules in two separate ET 200M racks and implement a software voting or 1-out-of-2 / 2-out-of-2 selection block in CFC.

Resolving the FM_DATA Parameter Interconnection Compilation Error

The driver block CNT_CTL / FM_CNT does not allocate local instance memory for the complex parameter structure of the 8 channels. Instead, it relies on an external data block structured according to UDT1 (FM_DATA). If the parameter FM_DATA on the CFC block pin is left unconnected, the CFC compiler aborts compilation with error: 'Parameter CFC(1).1.FM_DATA is not interconnected with a data source'. Generating a dedicated global DB based on UDT1 and linking it resolves the failure.

Digital Output Behavior in Frequency Measurement Mode

The FM 350-2 features 8 onboard digital outputs (DQ0 through DQ7):

  • In Counting Modes, the digital outputs can be linked to internal hardware comparators to switch instantly (with microsecond response) when a setpoint count is reached, bypassing CPU cycle times.
  • In Frequency Measurement Mode, the internal hardware comparator logic is disabled by the module firmware. The onboard digital outputs cannot be triggered automatically by frequency thresholds. Instead, the AS controller must evaluate the measured frequency cyclically in CFC and write to the digital outputs via control telegrams or standard DO cards.

Function Module Deployment Architecture Matrix

The following table compares configuration architectures for the FM 350-2 in S7-400 and S7-400H systems:

Deployment ArchitectureRedundancy MechanismDriver Block UsedHW Config Redundancy Supported?Failure Mode BehaviorSingle ET 200M RackNon-RedundantCNT_CTL (FB127)NoModule failure halts channel measurement.Dual ET 200M (Switched)Dual Independent ModulesTwo CNT_CTL instancesNo (Manual CFC Selection)Software logic fails over to backup module.Central S7-400 RackNot SupportedN/ANoFM 350-2 requires ET 200M or S7-300 backplane.Standard AI ModuleTrue Redundant PairPcs7AnInYes (Native H-System)Bumpless hardware failover on wire-break.

Step-by-Step Procedure to Configure FM 350-2 in PCS 7

Method 1: Creating and Linking the FM_DATA Data Block

  1. Open SIMATIC Manager.
  2. Open the FM 350-2 installation library (File > Open > Libraries > FM 350-2 Counter).
  3. Copy UDT1 (FM_DATA) from the library to the CPU's S7 Program > Blocks folder.
  4. In your project's Blocks folder, insert a new Data Block (e.g. DB350).
  5. In the DB properties, set the structural type to UDT1.
  6. Open the target CFC chart where block CNT_CTL or FM_CNT is placed.
  7. Locate input parameter FM_DATA.
  8. Drag and drop DB350 directly onto the FM_DATA block pin.
  9. Recompile CFC charts (Chart > Compile > Changes Only); confirm that the compilation error is resolved.

Method 2: Dual Module Software Redundancy in S7-400H

  1. In HW Config, insert an FM 350-2 in ET 200M Rack A, and a second FM 350-2 in ET 200M Rack B.
  2. Configure identical measurement parameters in both modules via the FM 350-2 configuration tool.
  3. In CFC, instantiate two CNT_CTL blocks, each linked to its respective module address and dedicated FM_DATA DB.
  4. Route both measured frequencies into an APL selection block (e.g. SelA02In or custom comparator logic).
  5. Use the module health status words to automatically switch to the secondary measurement if the primary reports a channel fault.

Verification

To verify FM 350-2 operation in PCS 7:

  1. CFC Compilation: Compile CFC charts. Confirm that compilation completes with 0 errors and zero unlinked parameter warnings.
  2. Communication Test: Go online in CFC Test Mode. Confirm that block parameter RETVAL returns 0 (indicating successful acyclic record exchange).
  3. Pulse Counter Verification: Inject a known pulse train or frequency from a calibrator into Channel 0. Verify that ACT_VAL updates dynamically and accurately in CFC.

Limitations and Operational Precautions

  • No Native Hardware Redundancy: Never attempt to configure FM 350-2 modules as redundant pairs in HW Config; S7-400H redundancy compilation will fail.
  • Backplane Speed: In ET 200M distributed racks on PROFIBUS DP, acyclic record communication via SFC58/59 introduces a latency of 10-50 ms; high-speed limit trips must use onboard counting comparators rather than AS software logic.
  • Power Supply Isolation: Ensure 24V encoder power supplies are properly bonded to the ET 200M backplane ground to prevent pulse jitter.

Engineer FAQ

Can FM 350-2 be inserted into an active ET 200M bus while the CPU is in RUN?

Yes, provided the ET 200M station is equipped with active bus modules (6ES7195-7HB00-0XA0) supporting hot-swapping.

Why does the module report an error during S7-PLCSIM testing?

S7-PLCSIM cannot emulate FM 350-2 internal ASIC registers or SFC58/59 record exchanges; hardware testing requires physical modules.

Can all 8 channels operate simultaneously at 20 kHz?

Yes, all 8 channels support up to 20 kHz input frequencies concurrently when using 24V standard signals.

Technical References

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