Resolving SIWAREX U FB242 Driver Generation Faults in PCS 7 V7.1

1. Problem Overview

Engineers integrating SIWAREX U weighing modules into a SIMATIC S7-400H redundant controller running PCS 7 V7.1 SP1 frequently encounter a fault pattern in which the standard block FB242 (v4.2) is correctly inserted into the CFC/SFC chart, yet the PCS 7 module driver concept does not produce the expected driver blocks RACKF (rack fault), MODF (module fault) and PERAF (periphery access fault). After compilation, the CFC compiler returns the warning "no hardware found for this base address of the configured SIWAREX module", and the driver instances remain unresolved.

This article documents the root cause, the affected product versions, and the validated field procedure that restores driver generation. The procedure is engineered for an S7-400H DP master system hosting 13 SIWAREX U modules, but applies to any S7-300/S7-400 installation in which the PCS 7 driver wizard cannot match a configured SIWAREX U against the HW Config catalog.

2. Affected Products and MLFB Mapping

The root cause of the driver-generation fault is an MLFB mismatch between the physical module installed on the field and the module type placed in the HW Config catalog. Engineers must distinguish between the following order numbers:

3. Root Cause Analysis

The PCS 7 driver concept (driver wizard) binds a CFC function block to a hardware address by matching the block's logical name to a module type and diagnostic address that exists in the S7 project. The matching algorithm inspects the HW Config catalog entry's order number (MLFB) and uses that as the lookup key for the symbol file shipped with the SIWAREX U PCS 7 configuration package.

If the catalog entry carries an MLFB that the configuration package does not register, the wizard cannot resolve the binding. The subsequent compile pass emits the diagnostic message "no hardware found for this base address" and the three driver blocks remain absent.

Specifically, in this fault scenario:

1. Engineer inserts SIWAREX U module type 7MH4950-2AA01 into the DP slave configuration in HW Config.
2. Engineer installs the SIWAREX U configuration package 7MH4683-3BA64 and inserts FB242 into the CFC chart at the same logical slot.
3. During compilation, the driver wizard queries the symbol database for MLFBs 7MH4601-2AA01 and 7MH4601-2BA01 only.
4. The wizard returns no match because the project contains 7MH4950-2AA01.
5. The driver instances RACKF, MODF, and PERAF are therefore not instantiated.
6. The CFC compiler issues the warning "no hardware found for this base address" for each SIWAREX instance.

4. PCS 7 Driver Concept Background

PCS 7 version 7.x replaced the legacy SIWA_U component self-diagnostic messages with the standardized driver generator. Instead of each device block internally raising fault flags, PCS 7 generates three standardized driver blocks at the chart level:

For a SIWAREX U occupying 16 bytes of input and 16 bytes of output data on a DP slave, all three driver blocks must be generated to provide complete diagnostic coverage for a single-channel weighing loop. Operators depend on MODF to detect load-cell cable breakage and PERAF to detect PROFIBUS communication loss to the module.

5. Prerequisites

Before applying the resolution, confirm the following items are present:

• PCS 7 V7.1 SP1 installed and licensed; PCS 7 closed during any setup activity.
• STEP 7 V5.4 SP5 or higher (matches PCS 7 V7.1) installed in the same engineering station.
• SIWAREX U configuration package for PCS 7, MLFB 7MH4683-3BA64, on CD or extracted to a local folder.
• S7-400H CPU 41xH (e.g., CPU 417-4H) with redundant PROFIBUS DP master system (e.g., two CP 443-5 Extended).
• 13 physical SIWAREX U modules installed on ET200M or DP/PA coupler stations.
• Local administrator rights on the engineering station to install the configuration package.

6. Step-by-Step Resolution Procedure

1. Close PCS 7 and STEP 7 on the engineering station. The configuration package installer requires both applications to be fully closed.
2. Insert the SIWAREX U PCS 7 configuration package CD (MLFB 7MH4683-3BA64) or navigate to the extracted package folder.
3. Execute setup.exe from the subfolder SIWAREX-U-SETUP-FOR-STEP7. Confirm any UAC prompts and accept the license agreement.
4. Wait for the installer to register the SIWAREX U symbol files, FB242 source, and the SIWAREX-U-SETUP-FOR-STEP7 catalog updates into the STEP 7 installation.
5. Re-launch STEP 7 and open the S7 project containing the S7-400H configuration.
6. Open HW Config for the affected DP master system.
7. For every slot that currently contains a 7MH4950-2AA01 entry: delete the existing SIWAREX U module from the slot.
8. Drag the SIWAREX U module type 7MH4601-2BA01 (preferred) from the HW catalog onto the same slot. The diagnostic address assignment and I/O address range must remain identical to the deleted module to preserve the binding with FB242.
9. If 16 byte input / 16 byte output consistency is required, double-click the module entry, navigate to Address > I/O Addresses, and verify the addresses match those expected by the CFC chart.
10. Save and compile HW Config (Station > Save and Compile).
11. Open the CFC chart containing the FB242 instance and re-run Chart > Compile (Charts > Compile).
12. Verify that the driver wizard now generates instances of RACKF, MODF, and PERAF beneath the FB242 block for each of the 13 modules.

7. S7-400H Specific Considerations

Operating SIWAREX U on an S7-400H redundant PROFIBUS DP master system requires additional configuration steps beyond the driver-generation fix.

For each of the 13 SIWAREX U modules, the CFC chart should reference FB242 at the logical address that matches HW Config. The driver wizard will generate RACKF, MODF and PERAF at the chart level; these blocks propagate faults to the OS picture via the standard PCS 7 driver-state mapping.

8. Verification Procedure

1. Open the S7 program in STEP 7 and navigate to the CFC containing the SIWAREX U charts.
2. Confirm the chart view shows FB242 with three child blocks: RACKF, MODF, PERAF. Each child should display a valid I/O address matching the module's diagnostic address.
3. Run Charts > Check > Consistency; the result must report zero errors and zero warnings referencing SIWAREX U.
4. Download the program to the S7-400H AS (both CPUs if H-system is in solo operation).
5. Trigger a forced diagnostic by briefly disconnecting the PROFIBUS connector on one SIWAREX U station; verify PERAF sets and the operator station raises a periphery-access fault alarm.
6. Reconnect the connector and verify the alarm clears within the configured PCS 7 acknowledgement time (default 4 seconds).
7. Inspect the WinCC process tag database to confirm that the SIWAREX U diagnostic bits are exposed in the standard driver picture, not in a custom faceplate.

9. Common Warnings and Error Codes

Beyond the headline "no hardware found for this base address" warning, engineers may encounter the following diagnostics during installation or compilation:

10. Compatibility and Firmware Notes

The PCS 7 V7.1 SP1 driver wizard was released in 2009. Field experience shows this service pack shipped with several known issues against newer library revisions, especially:

• SIWAREX U FB242 v4.2 - works correctly only against HW Config entries for 7MH4601-2AA01 / 7MH4601-2BA01.
• MICROMASTER 4 (MM440) drives - reported by multiple engineers as producing similar driver-generation mismatches under PCS 7 V7.1 SP1.
• SIMOCODE pro - motor management blocks require manual driver wiring on V7.1 SP1.
• CP 341 - serial communication modules occasionally lose driver binding after SP1 update.

When planning a PCS 7 upgrade that includes SIWAREX U, evaluate whether to:

1. Stay on V7.1 SP1 and apply the documented MLFB workaround in this article.
2. Upgrade the entire PCS 7 installation to a newer major version (V8.x or later), which provides updated SIWAREX U drivers and removes the MLFB legacy constraint.

11. Architectural Diagram

12. Field Commissioning Checklist

After applying the MLFB correction and re-compiling, use the following checklist to commission the SIWAREX U fleet on the S7-400H system:

1. Verify OB82, OB83, OB86 are present in the CPU program.
2. Confirm HW Config carries 7MH4601-2BA01 (or 7MH4601-2AA01) on all 13 slots.
3. Confirm CFC chart contains 13 instances of FB242 plus 39 driver blocks (3 per module).
4. Download program to both CPUs in the H-system.
5. Force a module-pull diagnostic on each SIWAREX U and confirm MODF raises at the OS.
6. Force a PROFIBUS break and confirm PERAF raises at the OS.
7. Perform a calibration with reference weights on each weighing station.
8. Document the calibration values in the SIWAREX U commissioning sheet supplied with the manual.

13. Safety and Standards

SIWAREX U on a non-fail-safe PROFIBUS DP connection is suitable for non-safety weighing applications. For SIL-rated weighing (overfill protection, batching interlocks), use SIWAREX WP231 or SIWAREX U in conjunction with a SIMATIC F-CPU and the appropriate safety configuration blocks. Refer to the IEC 61508 and IEC 61511 standards for the required SIL level of the application.