Resolving IM318-MS Module Configuration in S7-300 HW Config

Problem Overview: IM318-MS Not Found in S7-300 HW Config

An IM318-MS module with order number 6ES5318-2MM11 cannot be located inside the SIMATIC S7-300 hardware catalog of STEP 7 HW Config. Engineers restoring a project after a lost S7-300 CPU program typically attempt to insert the part into the S7-300 station by browsing the HW catalog tree (SIMATIC 300 > ... ), receive no match, and conclude that the GSD file is missing. The actual root cause is more fundamental: the IM318-MS is a SIMATIC S5 family PROFIBUS DP interface module designed for the ET 200U distributed I/O system, not an S7-300 native catalog object.

This article documents the diagnostic logic that separates a true GSD deficiency from a family-mismatch condition, lists the exact part numbers in the IM318 product tree that are interchangeable for hardware configuration purposes, and provides a working procedure for adding the module through the ET 200U GSD path in HW Config on STEP 7 V5.x.

Root Cause: S5 vs. S7 Catalog Architecture Mismatch

The STEP 7 HW Config catalog is partitioned by PLC family. The S7-300 catalog tree (SIMATIC 300 > SM-, FM-, CP-, IM- ... ) only contains modules designed for direct insertion into an S7-300 rail. The IM318 family, including the IM318-MS, was developed for the SIMATIC S5 ET 200U distributed I/O station and is therefore registered under the PROFIBUS DP slave catalog path, not under SIMATIC 300.

Three architectural facts drive this separation:

• Form factor: The IM318 family uses the ET 200U mechanical footprint and backplane, not the S7-300 rail.
• PROFIBUS DP slave role: The IM318 is a DP slave that requires a DP master (CPU 315-2 DP, CPU 317-2, CP 342-5, CP 443-5, or a third-party master) to assign parameters. It is not a master-capable interface for the S7-300 station itself.
• GSD registration scope: Siemens registers IM318 variants in the Profibus DP > ET200U subtree because the module is enumerated as a DP-V0 slave device with an ET 200U device identity, not as an S7-300 backplane element.

For official background on the IM 318 family and its product classification, refer to the Siemens Industry Support entry IM 318 - Product Information (ID 4205297). This entry confirms the module's positioning as a PROFIBUS DP interface element rather than an S7-300 slot module.

IM318 Module Family Identification

Multiple suffixes have shipped over the product lifecycle. Engineers restoring older installations must distinguish between them to select the correct GSD entry and to plan a migration if spare parts are no longer available.

Key differentiation points:

• The IM318-MS (2MM11) is the user's specific variant and is the original S5-era interface. It does not carry a separate GSD beyond the ET 200U family GSD.
• The IM318B (8MBxx) series replaced the original IM318 as Siemens rationalized the part numbering and consolidated firmware. Functionally compatible for most DP-V0 use cases.
• The IM318C (8MCxx) series added DP-V1 class-1 and class-2 services, allowing acyclic parameter and diagnostics data exchange in addition to the cyclic I/O of the IM318B.

Locating the IM318 GSD in STEP 7 HW Config

The IM318 does not require an external GSD import when using the catalog tree that ships with STEP 7. The GSD is bundled with the STEP 7 installation. Navigate the catalog as follows:

1. Open SIMATIC Manager and load the project (or create a new one matching the CPU on station).
2. Double-click Hardware to launch HW Config.
3. Open the catalog using View > Catalog (or press Ctrl+K).
4. Drill into: Profibus DP > ET200U
5. Within ET200U, select the IM318 entry that matches the physically installed module (IM318, IM318B, or IM318C as listed in the table above).

If the ET200U branch is missing from the catalog, the STEP 7 installation did not include the optional SIMATIC NET / PROFIBUS components. Reinstall with the STEP 7 V5.x + SP package and ensure the PROFIBUS DP Slave Catalog option is selected, or import the GSD manually:

1. Download the IM318 GSD from the Siemens Industry Support portal (search entry IM 318 - Product Information (ID 4205297) and follow the linked downloads).
2. In HW Config, choose Options > Install GSD File.
3. Browse to the downloaded *.gsd or *.gsg file and confirm.
4. Restart HW Config; the module will appear under Profibus DP > ET200U > IM318.

Step-by-Step Configuration of the IM318 in HW Config

The following procedure applies to STEP 7 V5.4 SP5 / V5.5 and later with the PROFIBUS DP catalog installed. The CPU on the master station must already be configured with a PROFIBUS DP master interface.

Prerequisites

• STEP 7 V5.4 SP5 or later with the PROFIBUS DP slave catalog option installed.
• A configured S7-300 station with a PROFIBUS DP master (e.g., CPU 315-2 DP, CPU 317-2 DP/PN, CPU 319-3 PN/DP) or a configured S7-400 station with a CP 443-5.
• Physical PROFIBUS DP network terminated per IEC 61158 (terminators ON at both ends, OFF in the middle).
• IM318 module MLFB confirmed by physical label.

Procedure

1. Open the DP master system. In HW Config, click the PROFIBUS(1) DP master system line (the horizontal cyan bar representing the subnet).
2. Insert the IM318. Drag the IM318 (or IM318B/IM318C if migrating) icon from the catalog (Profibus DP > ET200U) onto the DP master system line. STEP 7 will prompt for a PROFIBUS address.
3. Assign the PROFIBUS address. Enter a unique DP address in the range 1 to 125. The address must match the physical address set on the IM318 via the rotary switches on the front of the module. Typical address range: 3 to 32 for plant segments.
4. Configure the slot mapping. Right-click the IM318 station symbol and select Object Properties > Configuration. Map the ET 200U I/O slots to the process image of the CPU. For an ET 200U station with 8 slots (typical IM318 + up to 7 I/O modules), the I/O area defaults to 32 bytes input and 32 bytes output.
5. Set diagnostic behavior. In the same properties dialog, enable Diagnostic Interrupts and Process Interrupts as required by the application. The IM318 supports both diagnostic and process interrupts on the DP-V0 channel.
6. Save and compile. Press Ctrl+S, then choose Station > Save and Compile. Check the Compile Logs window for warnings such as Address area exceeded or Slot configuration mismatch.
7. Download to the CPU. With the target CPU online, select PLC > Download to Target. Confirm that the IM318 appears in the online view of the DP slaves.

Common Address Mapping Example

The exact address ranges depend on the slot configuration selected in the IM318 properties. Always cross-check against the Address Overview tab in HW Config before downloading.

Verification and Commissioning

After downloading, perform the following verification checks before placing the system in production mode:

1. Online DP diagnostics. In HW Config, right-click the IM318 station and select DP Slave Diagnostics. The expected response includes vendor ID 0x0 0 06 (Siemens AG) and the module's own PROFIBUS identification. A return of Slave not found indicates a wiring or address conflict.
2. Module status LEDs. The IM318 front panel has BF (Bus Fault), SF (System Fault), and ON LEDs. BF off, SF off, ON steady indicates normal cyclic operation.
3. I/O test pattern. Force a known value into a DO channel and read back via a connected DI or via the variable monitoring table (VAT) in STEP 7. The IM318 must return the expected state within one PROFIBUS cycle (typical 1 ms to 10 ms depending on baud rate and slave count).
4. Diagnostic buffer. Open the CPU's online diagnostic buffer (PLC > Diagnostic Buffer) and verify no Station Failure or Diagnostic Interrupt from DP Slave events are recorded for the IM318 address.

Diagnostic Interrupts and Error Codes

When the IM318 raises a diagnostic interrupt, the CPU places a diagnostic data block (typically 6 bytes header + module-specific payload) in the diagnostic interrupt OB (OB 82). The following channel-related error codes are commonly reported by the IM318 family on STEP 7 V5.x and TIA Portal equivalents:

For a complete list of channel errors, reference the diagnostic interrupt OB (OB 82) programming guide in the STEP 7 documentation set, and the SFC 59 / SFB 54 / SFB 52 function block descriptions for reading out the diagnostic buffer.

Migration Strategy: From IM318-MS to IM318B / IM318C

When the original IM318-MS hardware is no longer serviceable, plan a structured migration. The IM318B is the form-fit-function successor; the IM318C is the recommended target if the master supports DP-V1.

Pre-Migration Checklist

1. Verify DP master firmware supports the replacement module (no master change required for IM318B; IM318C may require master firmware update for DP-V1 class-2).
2. Capture the existing HW Config slot map and PROFIBUS address.
3. Verify the new module's GSD is registered in the STEP 7 catalog. If absent, import the GSD via Options > Install GSD File and restart HW Config.
4. Replace the module on the ET 200U backplane; set the same PROFIBUS address via the rotary switches.
5. Update the HW Config entry to point to the new MLFB and recompile.
6. Re-download to the CPU and repeat the verification steps in the section above.

Firmware and Compatibility Matrix

Troubleshooting Matrix

Notes on Long-Term Service and Documentation

The IM318 family is part of the SIMATIC S5 product line, which Siemens formally discontinued for new sales and migration assistance. The IM318-MS itself, identified by MLFB 6ES5318-2MM11, is generally available only as a service spare, and most plant operators have transitioned to IM318B-13 or IM318C-12. When a full migration is required, review the product information page on Siemens Industry Support at IM 318 - Product Information (ID 4205297) for the latest firmware bundles and for any official migration utilities that have been published for the S5-to-S7 transition path.