Configuring FM 350-2 Counter Modules on PROFINET Distributed I/O in SIMATIC PCS 7

In SIMATIC PCS 7 (such as v7.1 SP4 or later), integrating the FM 350-2 8-channel counter module (6ES7350-2AH01-0AE0) inside an ET 200M station connected via PROFINET (IM 153-4 PN) requires installing the FM 350-2 Configuration Package on the Engineering Station and utilizing the official PCS 7 Counter Module Driver Library. In HW Config, parameterize the counting modes using the FM 350-2 parameterization dialog, and in CFC, instantiate the dedicated driver block FMC_CNT (or CNT_CTL) to manage channel addressing, gate control, and acyclic data exchange via PROFINET record reading.

Architecture of High-Speed Counting in PCS 7: FM 350-2

In industrial automation plants running SIMATIC PCS 7, standard digital input cards cannot measure high-frequency pulse trains generated by flow meters, turbine flowmeters, optical encoders, or speed sensors due to cyclic execution scan limitations.

To process high-speed counting signals up to 20 kHz, Siemens provides the FM 350-2 Counter Module (6ES7350-2AH01-0AE0):
* 8 Independent Channels: Operates 8 discrete counting channels supporting 24 V incremental encoders, directional pulses, and NAMUR proximity sensors.
* Multi-Mode Operation: Supports continuous counting, periodic counting, single counting, frequency measurement, rotational speed measurement, and period measurement.
* Onboard Digital Outputs: Features 8 high-speed digital outputs capable of autonomous hardware tripping (e.g., stopping a dosing pump when a pulse count threshold is reached) with microsecond response times independent of CPU scan cycles.

The PROFINET Challenge: IM 153-4 PN vs Legacy PROFIBUS IM 153-2

Historically, Function Modules (FMs) were engineered exclusively for PROFIBUS DP using the IM 153-2 High Feature interface module. When modernizing to Industrial Ethernet / PROFINET IO using the IM 153-4 PN (6ES7153-4AA01-0XB0):

Communication Architecture Divergence:
On PROFIBUS, FMs utilize direct backplane P-bus interrupts and cyclic DP-V1 acyclic telegrams. On PROFINET, communication transits through the PROFINET IO Controller using asynchronous record data transfers (SFB 52 RDREC / SFB 53 WRREC).
Driver Compatibility:
Legacy STEP 7 counter function blocks (FC 0 CNT2_CTR) written for S7-300 CPUs cannot handle PCS 7 module driver generation or PROFINET record routing. In PCS 7, engineers must utilize the specialized SIMATIC PCS 7 FM 350-2 Library to ensure the compiler generates appropriate module drivers across PROFINET.

Required Software Packages: FM Configuration Tool vs PCS 7 Driver Library

To successfully configure the FM 350-2 in PCS 7, two distinct software packages must be installed on the Engineering Station:

FM 350-2 Configuration Package (Setup Tool):
Installs the hardware parameterization GUI into STEP 7 HW Config, allowing the engineer to double-click the module and set electrical input types, operating modes, and gate controls.
SIMATIC PCS 7 FM 350-2 Driver Library:
Supplies the technological CFC blocks:
* FMC_CNT (FB 350): The central channel driver block managing pulse counts, measurement values, and command handshakes.
* MOD_FM: The system module diagnostic block instantiated automatically by the module driver generator in system charts (@).

Hardware Addressing and Parameterization in HW Config

Configuring the FM 350-2 in HW Config requires strict address boundary adherence:

I/O Address Allocation:
The FM 350-2 occupies 16 continuous input bytes and 16 continuous output bytes in the S7-400 peripheral address space (e.g., PIW 256 to PIW 270).
Process Image Partition (PIP):
Because counting blocks typically execute in cyclic interrupt tasks (OB35), the module's I/O addresses must be assigned to the corresponding Process Image Partition (e.g., PIP 1 for OB35) or read directly via peripheral addressing.
Channel Parameterization:
Inside the parameterization dialog:
Select Signal Evaluation: e.g., Pulse and Direction, 24 V Incremental (x1, x2, x4).
Select Operating Mode: e.g., Continuous Counting or Frequency Measurement.
Define Gate Function: Software Gate or Hardware Gate via digital input.

CFC Block Architecture: FMC_CNT and CNT_CTL Integration

In the CFC chart, the technological counter block encapsulates all communication complexity:

Block Interconnections:
LADDR: Interconnected to the logical base address of the FM 350-2 configured in HW Config (e.g., 16#0100 for address 256).
CHANNEL: Configured with the channel number (0 to 7).
SW_GATE: Software gate command (1 = Enable counting, 0 = Inhibit).
COUNTVAL: Real-time 32-bit counter readout passed to supervisory logic.
MEASVAL: Real-time frequency or speed value.
Module Driver Automation:
When Generate module drivers executes during compilation, the compiler links diagnostic address pins (LADDR_DIAG) and error flags (QBAD) automatically into the @ system driver charts.

Comparison Table: FM 350-2 on PROFINET (IM 153-4 PN) vs PROFIBUS (IM 153-2)

The following table contrasts the deployment of FM 350-2 across fieldbus architectures:

Architectural MetricFM 350-2 on PROFINET (IM 153-4 PN)FM 350-2 on PROFIBUS DP (IM 153-2)Head Station InterfaceIM 153-4 PN (6ES7153-4AA01-0XB0)IM 153-2 HF (6ES7153-2BA10-0XB0)Fieldbus ProtocolPROFINET IO (100 Mbps Full Duplex)PROFIBUS DP (1.5 Mbps to 12 Mbps)Acyclic CommunicationAsynchronous Record Read/Write (SFB 52/53)DP-V1 Read/Write (SFB 52/53)System RedundancyS2 System Redundancy (on PN)Active Backplane Bus Redundancy (H-system)Driver LibraryPCS 7 FM 350-2 LibraryPCS 7 FM 350-2 LibraryTime Stamping (1 ms SOE)Not supported on IM 153-4Supported on IM 153-2 High FeatureMaximum Modules per RackUp to 8 or 12 modulesUp to 8 or 12 modules

Step-by-Step Configuration Workflow in PCS 7

Follow this verified engineering workflow to configure FM 350-2 on PROFINET:

Install Configuration Package:
* Run the SIMATIC FM 350-2 Configuration Package setup on the Engineering Station.
Configure Hardware in HW Config:
* Open the PROFINET IO line on the S7-400 CPU.
* Add the IM 153-4 PN distributed station.
* Insert the FM 350-2 Counter (6ES7350-2AH01-0AE0) into a free slot.
* Note the starting I/O address (e.g., 256).
Parameterize Counter Channels:
* Double-click the FM 350-2 module in HW Config to launch the Parameter Assignment Tool.
* Configure sensor evaluation, measuring modes, and gate functions for Channels 0 through 7.
* Save and compile HW Config.
Instantiate Driver Blocks in CFC:
* Open the desired CFC chart.
* From the FM 350-2 library, drag FMC_CNT onto the chart.
* Connect LADDR to the base address (256).
* Set CHANNEL to the desired channel index (e.g., 0).
Compile and Download:
* In CFC, click Chart > Compile > Entire program (ensure Generate module drivers is checked).
* Download the hardware configuration and CFC program to the S7-400 controller.

Verification

Verify that high-speed pulse counting operates deterministically:
1. Observe the physical status LEDs on the FM 350-2 module:
* SF (System Fault): Dark/off (indicates valid configuration and healthy bus communication).
* CR (Channel Running): Green LEDs illuminate when software gates are enabled and pulses are received.
2. In CFC Test Mode, observe FMC_CNT:
* Set SW_GATE = TRUE.
* Apply test pulses from a signal generator; verify that COUNTVAL increments dynamically matching input frequency.
3. Verify that QBAD = FALSE and QUALITY = 16#80 (Good), confirming healthy module driver integration.
4. Test hardware tripping: Verify that reaching the configured comparator count immediately energizes the designated onboard digital output.

Limitations and Operational Precautions

Active Bus Modules: While IM 153-4 PN supports hot-swapping modules, always ensure the active backplane bus modules (6ES7195-7HB00-0XA0) are properly seated.
Shielding High-Frequency Pulse Lines: Pulse signals up to 20 kHz are highly susceptible to electromagnetic interference from nearby variable frequency drive (VFD) motor cables. Always use shielded, twisted-pair cables with 360-degree shield bonding at cabinet entry.
Power Supply Commonality: The FM 350-2 sensor supply and counter inputs must share a common ground (0 VDC) with the module logic power supply to prevent floating voltage errors.
Commercial Accuracy: Ensure that the FM 350-2 module (6ES7350-2AH01-0AE0) and IM 153-4 PN interface (6ES7153-4AA01-0XB0) are procured according to manufacturer specifications. Validate license allocations with an authorized Siemens distributor quotation.

Engineer FAQ

Can FM 350-2 be configured using standard STEP 7 GSD files instead of the Configuration Package?

No. The FM 350-2 requires the proprietary parameterization tool to configure channel modes, pulse multipliers, and gate triggers; generic GSD files lack this configuration interface.

Does the FM 350-2 continue counting if the S7-400 CPU enters STOP mode?

Yes. The FM 350-2 possesses onboard microprocessors and counter ASICs that continue counting pulses independently of the CPU state, provided 24 VDC module power is maintained.

How many FM 350-2 modules can be placed in a single ET 200M station?

Up to 8 FM 350-2 modules can be installed in a single ET 200M rack, providing up to 64 independent high-speed counting channels.

Can FM 350-2 be used for rotational speed measurement in RPM?

Yes. When parameterized for 'Rotational Speed Measurement', the module calculates RPM directly based on configured pulses per revolution and outputs the scaled speed value to MEASVAL.