SIWAREX MS Configuration Package: Manual, SIWATool & S7-200 Library Integration

Overview

The SIWAREX MS (Siemens Weighing Extension Module – Multi-Scale) is a precision weighing electronics module designed for direct integration into the SIMATIC S7-200 automation system. It operates as a single-channel, high-resolution weighing front-end that captures load cell signals, performs digital filtering, and exchanges scaled weight, status, and diagnostic data with the S7-200 CPU over the I/O backplane. The module is engineered for use in platform scales, hopper scales, dosing systems, and force measurement applications where deterministic weight acquisition is required at the controller level without a separate panel-mounted indicator.

Configuring the SIWAREX MS requires three distinct software assets:

1. The SIWATool MS Windows commissioning software (entry ID 22601567) – used for parameterization, calibration, and diagnostics.
2. The SIWAREX MS manual (entry ID 22600601) – the device hardware, wiring, and parameter reference.
3. The Microautomation Set 6 / SIWAREX MS library (entry ID 22354065) – the STEP 7 Micro/WIN function block library that allows the S7-200 CPU to communicate with the module.

All three are available through the Siemens Industry Online Support portal at no charge for the documentation and library; SIWATool itself is provided as a demonstration viewer that exposes read-only parameter data without a paid license.

Locating the SIWAREX MS Configuration Package

Siemens distributes technical documentation and software under unique numeric identifiers called Entry IDs. These IDs are referenced from data sheets, manuals, and product pages. The following Entry IDs correspond to the SIWAREX MS deliverables:

To download any of these assets, navigate to the Siemens Industry Online Support entry search at support.industry.siemens.com, paste the Entry ID into the search field, and select the corresponding result. Direct retrieval paths follow this template:

Filenames typically appear as SIWAREX_MS_Library_add_V1d0_en.pdf for the library attachment and SIWATool_MS_Setup_V*.exe for the tool installer.

SIWATool MS Functionality and Licensing

SIWATool MS is the PC-based commissioning software for the SIWAREX MS module. It communicates with the module over the RS-232 service interface (COM port) using the proprietary SIWATOOL protocol at 9,600 bit/s, 8 data bits, no parity, 1 stop bit. The tool provides:

• Live weight display with selectable units (kg, g, lb, t).
• Parameter upload/download (DR n – Data Records).
• Load cell calibration wizard (zero, span, simulation).
• Diagnostic buffer and command execution log.
• Firmware identification and version check.

Despite the read-only restriction, the demo is useful for the following engineering tasks:

1. Verifying wiring and load cell excitation voltage (approximately 5 V DC across the cell bridge).
2. Reading the current firmware version (DR 3 field FW_VER).
3. Capturing the existing parameter set for documentation prior to replacement.
4. Logging live weight for acceptance testing (CSV export is not available in demo mode).

SIWAREX MS Library for STEP 7 Micro/WIN

The SIWAREX MS Library is delivered as a ZIP archive containing a Micro/WIN add-in, a sample S7-200 project, and a PDF function reference. The library is the only recommended method of communicating with the module from the S7-200 CPU; the module does not use a standard S7-200 expansion I/O map and requires explicit I/O handshake via the FBs provided.

The core Function Blocks supplied in the library are:

Each FB consumes a defined amount of V memory and a single SMB (Special Memory Byte) area for the handshake. The library README specifies the allocation in the file SIWAREX_MS_Library_add_V1d0_en.pdf (available directly from the Siemens support entry linked in the references section of this article).

Installing the Library in STEP 7 Micro/WIN

Prerequisites:

• STEP 7 Micro/WIN V4.0 SP6 or higher installed on a Windows PC with an RS-232 PPI/MPI cable or USB-PPI adapter.
• S7-200 CPU model 224, 224XP, 226, or 226XM. The library has not been tested against the CPU 221/222 as these lack the required work memory for the FB instance DBs.
• SIWAREX MS module seated in the S7-200 rack and DIP switches set to a unique scale address (1 through 31, default 1).

Installation procedure:

1. Extract the library ZIP to a known directory (e.g., C:\Siemens\SiwarexMS\).
2. Launch STEP 7 Micro/WIN and open the target project.
3. From the menu bar, select File > Add Library (or in older Micro/WIN versions, Tools > Library > Add).
4. Browse to the extracted directory and select SIW_MS.lib.
5. Confirm the prompt to copy the FBs into the project library. The five FBs listed in the table above will appear under Library > SIW_MS in the Instruction Tree.
6. From File > Add File, add the SIW_MS_Sample.mwp sample project to a temporary scratch project to inspect the instance DB structure and the symbol table conventions.

The library PDF provides a fully annotated ladder example for OB1 that demonstrates the call sequence: SIW_MS_INIT on first scan, SIW_MS_READ every 100 ms, and SIW_MS_WRITE_CMD triggered by an HMI bit. A simplified ladder sequence is reproduced below.

NETWORK 1    // Initialize on first scan
SM0.1       SIW_MS_INIT  EN
            SIW_MS_INIT  ScaleAddr = 1
            SIW_MS_INIT  Error    = VW200
            SIW_MS_INIT  Done     = V200.0

NETWORK 2    // Read weight continuously
SM0.5       SIW_MS_READ   EN
            SIW_MS_READ   ScaleAddr = 1
            SIW_MS_READ   Weight    = VD210   // REAL, kg
            SIW_MS_READ   Status    = VB214
            SIW_MS_READ   Error     = VW216

NETWORK 3    // Tare command from HMI
I0.0        SIW_MS_WRITE_CMD  EN
            SIW_MS_WRITE_CMD  ScaleAddr = 1
            SIW_MS_WRITE_CMD  CmdCode   = 16#01   // 0x01 = Tare
            SIW_MS_WRITE_CMD  Done      = V220.0
            SIW_MS_WRITE_CMD  Error     = VW222

Data Record (DR) Architecture

The SIWAREX MS stores all scale parameters, calibration data, and command bytes in a fixed set of Data Records (DR n). Each DR is a 16-byte block addressed by a 1-byte index. The most relevant records for the integrator are:

FB 104 (SIW_MS_PARAM) is the generic access path: populate the DR index input, set the R/W flag, and provide a pointer to a 16-byte V memory buffer. The library handles the byte-level framing and the CRC verification defined in the SIWAREX MS manual.

Hardware Configuration and Wiring

The SIWAREX MS occupies a single slot in the S7-200 expansion rack. The front panel exposes a 12-pin screw terminal block for the load cell and a 9-pin Sub-D for the RS-232 service port. The terminal assignment is:

Use a shielded 6-wire cable for installations where the load cell cable run exceeds 5 m. The shield must be bonded to terminal 12 and to the grounded enclosure of the module; do not ground the shield at the load cell end to avoid ground loops. The module's measuring rate is fixed at 50 Hz internal; the S7-200 handshake is fully decoupled from this rate.

Verification and Acceptance Test

After the library is installed and the program is loaded, perform the following commissioning verification:

1. Power the S7-200 with the SIWAREX MS module seated. Observe the module's RDY LED state: solid green indicates a healthy module, blinking red indicates a parameter error, solid red indicates hardware fault.
2. Run the sample project. Confirm that FB 100 sets Done = 1 within 2 seconds of the first scan, indicating successful module initialization.
3. Monitor VD210 (weight in kg) in the Micro/WIN status chart. Apply a known test weight and confirm the displayed value is within the expected accuracy class (typically 0.05% of full scale at 3 mV/V).
4. Trigger a tare via I0.0 and verify the displayed weight returns to 0.000 kg.
5. Power cycle the S7-200 and confirm the SIWAREX MS retains the zero and span values. Calibration data is stored in non-volatile memory on the module itself and is preserved independently of the S7-200's retentive memory.
6. Use SIWATool MS demo to read DR 3 and confirm the order number (6SE7 130-1AA00-0AA0 for the standard MS, or 6SE7 130-1AA01-0AA0 for the MS FCC variant) and the firmware version are visible. This step is also the most reliable way to record the as-installed configuration for the documentation pack.

Troubleshooting Matrix

Integration with the Starter Pack and Optional Hardware

Siemens historically offered a SIWAREX MS Starter Pack bundling the module, a load cell, the SIWATool cable, and the printed manual. Regional Siemens sales offices can confirm current availability, pricing, and any equivalent bundle offerings (such as the SIWAREX WP231 or SIWAREX FTC variant starter kits). For new projects, the SIWAREX WP231 module (for S7-1200) and the SIWAREX FTC (for S7-300/400/ET 200S) are functionally equivalent successors with modern SIWATool V7 connectivity; the MS remains the correct choice when the controller platform is the legacy S7-200.

Frequently Asked Questions