Resolving SM331 AI 2x12Bit Catalog Absence in TIA Portal V13

Problem Statement: SM331 AI 2x12Bit Module Not Visible in TIA Portal V13 Hardware Catalog

Engineers commissioning, training on, or maintaining legacy SIMATIC S7-300 systems frequently encounter a missing device when they try to add the SM331 AI 2x12Bit analog input module with order number 6ES7331-7KB01-0AB0 in the TIA Portal V13 hardware catalog. The module does not appear in the device tree under SIMATIC S7-300 > Analog input/output > SM331, and no entry for "AI 2x12Bit" is generated when the user expands the catalog node. Attempting to drag-and-drop the device into the device view produces no result, and a manual search by order number in the catalog search field also returns zero hits.

According to the original Siemens technical support response, this module was phased out in 2004 and is no longer included in the TIA Portal hardware catalog. No Hardware Support Package (HSP) or catalog update is available to add the legacy order number back into the TIA Portal device pool. Engineers working on educational, training, or maintenance projects therefore cannot configure the module inside TIA Portal V13 (or any subsequent TIA Portal version through V20) without first applying a workaround.

Affected Hardware Identification

Confirm the exact MLFB (machine-readable product designation, also called the order number) printed on the front panel of the physical module before selecting a remediation path. The descriptive label "SM331 AI 2x12Bit" is shared by multiple variants in the S7-300 family; only the order number unambiguously identifies the affected module.

Root Cause: TIA Portal V13 Catalog Behavior and Lifecycle Filtering

The TIA Portal hardware catalog is built from a curated device database that ships with the installation media. Modules are included only if they meet two conditions at the time of release:

1. The product is in active sales status (not announced for phase-out or already phased out) at the TIA Portal release date.
2. The product is covered by an installed Hardware Support Package (HSP) or by the base catalog revision of the installed TIA Portal version.

The original 6ES7331-7KB01-0AB0 was phased out in 2004, ten years before TIA Portal V13 was released. Because the module was already out of active sales for a decade, it was never integrated into the TIA Portal V13 (or V14, V15, V16, V17, V18, V19, V20) hardware catalog. The TIA Portal online help explicitly states that the component selection in the "Catalog" pane contains the installed hardware components and that you move devices or modules you want from the catalog to the device view; legacy devices that were never added to the catalog cannot be retrieved by any in-product action. See the TIA Portal V20 hardware catalog documentation for the catalog structure and HSP behavior.

The Siemens support response for this specific issue is unambiguous: "this module is phased out since 2004 and not supported in TIA Portal. There is no Support Package/Catalog Update available!"

TIA Portal vs. STEP 7 V5.x Compatibility for Legacy S7-300 Hardware

Engineers working with S7-300 systems must understand the split between the two Siemens programming environments:

The original Siemens support response notes: "Step7 V5.x can however only program the S7-300 and S7-400 family of PLCs." This is a deliberate separation: TIA Portal's newer engineering paradigm does not duplicate the entire legacy S7-300 module catalog because STEP 7 V5.5 remains the supported, actively maintained toolchain for legacy S7-300/400 hardware. STEP 7 V5.5 is still kept up to date and is the official environment for installing, configuring, and programming the 6ES7331-7KB01-0AB0 module.

For this reason, the first remediation path is to install or activate STEP 7 V5.5 (or a later V5.x version) on the engineering workstation and use SIMATIC Manager's HW Config to add the SM331 module to the S7-300 rack. The module, the rack, and the S7-300 CPU can all be configured even if the workstation also has TIA Portal installed — the two toolchains coexist on the same PC.

Hardware Support Package (HSP) Installation in TIA Portal

For modules that are in the active catalog but missing from the local TIA Portal installation, the standard mechanism is to install a Hardware Support Package (HSP). HSPs are downloadable archives from the Siemens Industry Online Support. They are imported via Options > Support Packages > Install in TIA Portal, after which the new modules become available in the hardware catalog under the appropriate path (for example, SIMATIC S7-300 > Analog input/output > SM331).

For the 6ES7331-7KB01-0AB0, no HSP exists because the module was phased out long before the TIA Portal catalog window opened. Attempting to import any S7-300 HSP and search for the part number returns no result. This confirms the official Siemens support position: the module is not recoverable in TIA Portal by any in-product action.

Solution Path 1: Migrate to the Successor SM331 Module (6ES7331-7KB02-0AB0)

If the application can tolerate a brief hardware swap, replace the legacy module with the active successor 6ES7331-7KB02-0AB0. The successor module is pin-compatible with the original at the backplane connector and the front-side terminal block, so the existing S7-300 rack slot, the backplane wiring, and the field-side terminal wiring can be retained.

Hardware Compatibility

Replacement Procedure

1. Power down the S7-300 rack and apply lock-out/tag-out (LOTO) procedures. Remove the 24 V DC field supply from the analog module's front connector.
2. Record the wiring at the front connector: each wire's terminal number, signal type, and channel assignment. The SM331 AI 2x12Bit uses terminals 1 to 20 with two channels typically assigned to terminal pairs (e.g., channel 0 on 1-2 sense, 3-4 measurement; channel 1 on 5-6 sense, 7-8 measurement; terminals 19-20 for the 24 V loop supply when used).
3. Unlock the front connector (slide the release tab), disconnect the front connector from the module, and place it on a clean surface.
4. Press the module release lever at the top of the module and swing the module out of the rack. The module is released from the backplane bus connector.
5. Insert the new 6ES7331-7KB02-0AB0 module in the same slot. Ensure the backplane connector engages fully.
6. Re-seat the front connector. The screw terminals accept the same wire terminations as the original.
7. Re-apply the 24 V DC field supply and rack power. Verify the SF (group fault) LED is off.
8. Re-download the STEP 7 / TIA Portal hardware configuration and user program.

Solution Path 2: Use STEP 7 V5.5 for the Original Module

If hardware replacement is not an option — for example, the system is in a validated production line and a revalidation cycle is not feasible — keep the 6ES7331-7KB01-0AB0 module and use STEP 7 V5.5 (or the latest V5.x service pack) as the configuration and programming environment.

Installation and Project Setup

1. Install SIMATIC STEP 7 V5.5 with the latest Service Pack and Hotfix. The product DVD (or downloaded installer) is the official Siemens delivery medium. License keys are transferred with the Automation License Manager (ALM).
2. Open SIMATIC Manager and create a new S7-300 project. Add an S7-300 station with the matching CPU order number (e.g., 6ES7315-2EH14-0AB0 or the appropriate CPU variant in use).
3. Open HW Config from the station object. The hardware catalog on the right side of HW Config includes the full SM331 family, including the legacy 6ES7331-7KB01-0AB0 entry.
4. Drag the SM331 AI 2x12Bit entry onto the selected rack slot. Slot 4 is the default; the module can be placed in any slot from 4 to 11 (depending on the rack type and CPU).
5. Double-click the module to open its properties. Configure the measurement type per channel (voltage, current, RTD, or thermocouple) and the integration time / resolution. The HW Config dialog writes the configuration to the module on the next download.
6. Save and compile the hardware configuration. Download to the CPU via PLC > Download to Target or via online accessible nodes.

Reading the Module in the User Program

After configuration, the analog values are read from the process image of the analog module. The base address is assigned in HW Config (e.g., PIW 256 and PIW 258 for the two channels). Use the standard FC105 "SCALE" or FC106 "UNSCALE" blocks from the STEP 7 standard library to scale the raw integer (0 to 27648 nominal range) to engineering units, or read the value directly and apply the linear scaling formula:

// Unscaled raw value from channel 0
L PIW 256
T #iRawValue

// Scale 0...27648 to 0.0...100.0 (engineering units)
CALL "SCALE"
IN  := #iRawValue
HI_LIM := 1.000000e+002
LO_LIM := 0.000000e+000
BIPOLAR := FALSE
RET_VAL := #iScaleRet
OUT := #rEngValue

Diagnostic Interrupt (OB82) Structure

When a diagnostic event occurs on the SM331 module, the S7-300 CPU calls OB82. The local variables of OB82 contain the diagnostic data structure. Key fields include:

Solution Path 3: Educational Platform Migration to S7-1200

For training and classroom use — the original use case described in the source — Siemens recommends migrating to the S7-1200 family. TIA Portal V13 SP1 (and later) added the ability to simulate the S7-1200 PLC with the integrated PLCSIM, which is ideal for instructor-led and student-led training without physical hardware.

Benefits of the S7-1200 Migration Path

• Native TIA Portal support: All S7-1200 CPUs (CPU 1211C, 1212C, 1214C, 1215C, 1217C) and signal modules (SM1231, SM1232, SM1234) are in the base TIA Portal V13 hardware catalog.
• Integrated PLCSIM: TIA Portal V13 SP1 added S7-1200 simulation. The student can write, download, and test a complete program without connecting to real hardware.
• Modern programming model: Optimized data blocks, symbolic addressing, and IEC 61131-3 languages are consistent across the S7-1200 and S7-1500 families.
• Analog input replacement: The SM1231 AI4x13Bit (6ES7231-4HD30-0XB0) and SM1231 AI8x13Bit (6ES7231-4HF30-0XB0) provide 4- and 8-channel analog inputs at 13-bit resolution with native TIA Portal configuration.

PLCSIM Setup for S7-1200 in TIA Portal V13 SP1

1. Install TIA Portal V13 SP1 (or later) on the engineering workstation. PLCSIM V13 SP1 (or later) is included in the TIA Portal installation package as an optional component.
2. Create a new project and add an S7-1200 CPU (e.g., CPU 1214C DC/DC/DC, 6ES7214-1AG40-0XB0).
3. Open the project, switch to the project view, and select the CPU in the device view.
4. From the menu, select Online > Simulation > Start (or press Ctrl+Shift+U). TIA Portal starts the PLCSIM instance and connects it to the project.
5. Download the hardware configuration and the user program to the simulated CPU. The simulated CPU executes the program, updates the process image, and responds to all online functions (monitor, force, trace).
6. For the SM1231 analog input, inject test values via the PLCSIM variable table. Set the input word (e.g., IW64) to a known raw value (e.g., 0 for 0 V, 27648 for 10 V) and confirm the user program scales the value correctly.

To configure the S7-1200 analog input in TIA Portal V13 (or later), open the device view, add the SM1231 module, and open the module's properties. Set the input type (voltage or current) and the range (e.g., 0 to 10 V or 4 to 20 mA) per channel. The process image is updated automatically and is accessible in the user program via the symbolic tag name assigned in the PLC tag table.

Configuration Migration: Old vs. New Module Property Pages

The configuration dialog of the original SM331 (in STEP 7 V5.5 HW Config) and the successor SM331 (in TIA Portal V13+) are conceptually similar but differ in operational flow.

When migrating a project from the original SM331 to the successor SM331 within TIA Portal, no application code changes are required. The input word addresses (PIW) remain the same when the module is placed in the same slot. The scaling function blocks (FC105, FC106, or TIA Portal's NORM_X and SCALE_X) work identically because the raw value encoding is preserved across the 12-bit and 14-bit integration modes.

Measurement Type and Wiring Reference

The SM331 AI 2x12Bit supports a broad set of measurement types. The wiring depends on the signal type and the channel assignment. Use this table as a quick reference when commissioning the original or successor module:

Hardware Installation and Replacement Procedure (Step-by-Step)

1. De-energize. Open the main disconnect and apply lock-out/tag-out. Remove the 24 V DC supply to the analog module.
2. Document the wiring. Photograph the front connector, or draw a wiring diagram with each terminal number, signal tag, and channel assignment. The SM331 front connector is 20-pin; pin 1 is the upper-left when viewed from the front.
3. Unlock the front connector. Press the release tab at the top of the connector and pull it forward.
4. Remove the module. Press the module release lever at the top of the module and swing the module out of the rack. Lift it clear of the backplane connector.
5. Insert the replacement. Slide the new 6ES7331-7KB02-0AB0 (or the original 6ES7331-7KB01-0AB0 if returning the module to service) into the same slot. Ensure the backplane connector engages fully; the module should click into place.
6. Re-seat the front connector. Slide the front connector onto the module pins and lock the release tab.
7. Verify the wiring. Re-check each terminal against the documented diagram. Confirm that the shield (if used) is landed on the module's shield terminal, not on a power terminal.
8. Re-apply power. Restore the 24 V DC supply and the rack power. Watch the SF LED on the new module during power-up. The SF LED should be off within 2 seconds if the configuration matches the inserted module.
9. Re-download the configuration. In TIA Portal or STEP 7 V5.5, perform a full download of the hardware configuration and the user program to the CPU. Perform a CPU restart (STOP then RUN) if requested by the engineering tool.
10. Verify the analog inputs. Use a calibration source (e.g., a precision voltage calibrator or a 4-20 mA source) to inject a known signal on each wired channel. Read the process image word (PIW) and confirm the scaled engineering unit matches the expected value within the module's accuracy spec.

Verification and Commissioning Checks

After applying any of the three remediation paths, run the following verification checks to confirm the system is operating correctly:

1. Module presence. Open the online diagnostics in TIA Portal or STEP 7 V5.5. Confirm that the SM331 (or SM1231) module is detected in the expected slot with the correct order number and firmware version.
2. SF LED off. The group-fault LED on the front of the module must be off. An illuminated SF LED indicates a configuration mismatch, a wire break, or a hardware fault.
3. Channel value plausibility. Apply a known reference signal (e.g., 5.000 V on a 0 to 10 V channel) and verify the scaled engineering unit in the user program matches within the module's accuracy spec (typically ±0.5 % of full scale for the 12-bit SM331, ±0.3 % for the 14-bit integration mode).
4. Diagnostic interrupt path. Force a wire break on a 4-20 mA channel and confirm that OB82 is called and that the diagnostic buffer in the CPU contains the expected entry. Restore the loop and confirm OB82 is called again with the "outgoing" event.
5. User program execution. Run the S7 program for at least 5 minutes in RUN mode and confirm the scan time, the cyclic interrupt OB (if used), and the analog value updates are operating within expected bounds.

Troubleshooting Matrix

Recommendations for Education and Long-Term Maintenance

For a training environment where the 6ES7331-7KB01-0AB0 is being used as a teaching aid, the most sustainable path forward is to migrate the lab to the S7-1200 family. TIA Portal V13 SP1 supports PLCSIM for the S7-1200, which removes the dependency on a physical rack for the majority of classroom exercises. The S7-1200 SM1231 analog modules have a much simpler configuration model and the web server of the CPU provides a built-in dashboard for student visualization.

For long-term maintenance of an installed S7-300 base, retain a STEP 7 V5.5 license and engineering workstation in addition to the TIA Portal workstation. STEP 7 V5.5 is the supported engineering environment for any S7-300 module that pre-dates the TIA Portal hardware catalog window. The two toolchains coexist on the same PC and can use the same Ethernet / MPI / PROFIBUS connection to the rack.

FAQ