Configuring ET200L SC Modules in STEP 7 5.5: TB16SC Slot Workarounds

Engineers migrating a STEP 5 system that uses ET 200L distributed I/O with SC (Signal Conditioning) modules frequently hit a wall in SIMATIC STEP 7 V5.5: the hardware catalog inserts the ET 200L base block, but the lines for the TB16SC terminal block and the individual SC module slots (A, B, C…) never appear. The configuration compiles without errors, the PLC communicates with the digital base block, and yet every output addressed on the SC side stays at zero while the program visualization shows the bit as ON. This article documents the root cause, the three field-proven workarounds, and the migration path out of the dead-end.

1. Problem Description: SC Slots Disappear in the Hardware Catalog

The fault presents itself in the SIMATIC Manager Hardware Configuration editor (HW Config) when an ET 200L block is dragged from the catalog into the PROFIBUS DP rack:

• The base block (e.g., 6ES7 131-1BL11-0XB0, 16 DI 24 V DC) installs correctly and occupies its DP slave address.
• The expected lines for the TB16SC terminal block and the A/B/C… SC module slots are missing.
• The GSD file imported for the device lists only four I/O slots (the digital base block channels).
• If the field engineer copies a properly configured ET 200L-SC from an existing project, the SC slots appear, can be edited, and the configuration is retained after a save — but the catalog-installed object from scratch has no SC slot rows at all.

At runtime the symptom is silent: no diagnostic interrupt, no SF LED on the ET 200L, no entry in the diagnostic buffer. The S7 master simply never downloads the SC slot assignment to the remote rack, so the SC modules power up un-configured and the outputs do not energize even when the process image bit is forced to 1.

2. Affected Hardware and Order Numbers

The following catalog numbers appear in projects that exhibit the problem. Only part numbers explicitly present in the source project context are listed; other ET 200L family members follow the same configuration rules and exhibit the same fault.

3. Root Cause: GSD vs. Type File (GSx) Architecture

Siemens publishes two classes of device description for ET 200L:

1. GSD file (Device Master File): Plain-text PROFIBUS device description consumed by every PROFIBUS configurator, including STEP 7 HW Config. The GSD only contains the four I/O slots that belong to the digital base block. SC slots are not present in any shipped GSD for the ET 200L family.
2. Type file (.GSx, language-specific): A proprietary Siemens type file that adds the SC sub-rack rows (TB16SC line plus the A/B/C… SC module slots) on top of the base block. Type files are larger than the corresponding GSDs and are only consumable by older STEP 7 versions that still support the KGP/ET 200L slave group.

STEP 7 V5.5 still accepts the GSD but rejects the type file with the diagnostic:

SIE_8027.GSG describes a KGP/ET 200L slave.
Slaves of this group based on GSD file (type file) are presently not supported.

That single message is the entire root cause. STEP 7 V5.5 cannot install the type file, so the catalog entry only knows about the four base-block slots, and the SC configuration string that should be downloaded to the rack is never generated. The hot-swap behaviour described in the field reports — where the SC I/O works after a power transfer from an S5 master to an S7 master but stops working after a cold start — is direct evidence of this: the surviving master had previously downloaded the SC slot mapping to the ET 200L's local configuration memory, and that mapping persists until the rack is power-cycled, at which point the S7 master has nothing to send.

For background on how the hardware configuration is downloaded over PROFIBUS and what the master must transmit to a slave during startup, the Siemens support entry Networking a PROFINET IO device with a SIMATIC S7 in STEP 7 V5 documents the equivalent flow for PROFINET IO, including the "PLC > Ethernet > Verify Device Name" path that mirrors the DP "Verify Station Address" used during ET 200L commissioning.

4. The SIE_8027.GSG Error Decoded

The message above is logged by the STEP 7 hardware catalog installer (the Install HW Updates tool) when an attempt is made to register the type file. The SIE_8027.GSG file is the language-specific ET 200L type file (German in this case; English variants are SIE_8027.GSE, French SIE_8027.GSF, Italian SIE_8027.GSI, Spanish SIE_8027.GSS). The diagnostic string is a hard-coded limitation of the STEP 7 V5.5 catalog loader: the KGP/ET 200L family was the last slave group in the catalog to retain type-file-based slot definition, and the loader was never updated to import it in V5.5.

5. Workaround 1 — Copy-Paste from a Known-Good ET 200L Project

The cleanest in-V5.5 workaround exploits the fact that the SC slot rows are normal HW Config objects once they exist. They can be cut, copied, pasted, edited, and saved without re-importing the type file.

5.1 Prerequisites

• A second project (or a project archive .zip) that contains an ET 200L with the SC sub-rack fully configured.
• The same base-block order number (or a compatible variant) installed in both projects.
• STEP 7 V5.5 with read/write access to both projects.

5.2 Procedure

1. Open the source project in SIMATIC Manager and launch HW Config.
2. Locate the ET 200L station on the PROFIBUS DP master system and click the base block to select the entire station (not just the block).
3. Press Ctrl+C to copy the station object to the clipboard.
4. Open the target project, navigate to the same PROFIBUS master system, and click on an empty DP address slot.
5. Press Ctrl+V. HW Config pastes the entire station, including the TB16SC line and the populated SC module rows.
6. Adjust the DP slave address and the I/O addresses of the pasted SC modules to match the target wiring if necessary.
7. Station > Save and Compile (Ctrl+S) — confirm the compile log shows no errors.

5.3 Caveats and Limitations

• The pasted station inherits the source project's GSD revision. If the target project uses a different GSD revision, the paste may be rejected or the slot structure may be silently re-initialised to the four-slot default.
• Order-number compatibility: the pasted station was built around a specific base block (e.g., 6ES7 131-1BL11-0XB0). If the target has a 6ES7 131-1BH11-0XB0 with a different I/O address map, the address assignments must be re-checked after paste.
• The pasted SC slot definitions remain valid only for the same type file revision that generated them. Re-installing HW Updates that touch the ET 200L can invalidate the structure; back up the project before any catalog update.

6. Workaround 2 — Live Power Transfer from an S5 Master

This is a field workaround, not a configuration technique, but it is the only documented way to get SC I/O working with a STEP 7 V5.5 master when no working SC slot structure can be built inside the project. It works by exploiting the ET 200L's retain-on-power-loss behaviour for the SC configuration.

6.1 Procedure

1. Leave the ET 200L-SC rack powered and the PROFIBUS cables connected to the existing S5 master.
2. Boot the S5 master so that it completes its PROFIBUS startup and downloads the SC slot mapping to every ET 200L station.
3. With the racks still powered, transfer the PROFIBUS connectors from the S5 master to the S7 master.
4. Power up the S7 master without power-cycling the remote racks. The S7 master performs DP startup; the ET 200L stations keep the SC mapping that the S5 master downloaded and continue to operate the SC I/O correctly.

6.2 Why It Works

The SC slot configuration is stored locally in the ET 200L's configuration memory. The DP master is not required to re-transmit it on every startup — the master only re-transmits it when the slave reports a configuration mismatch, which it does not do as long as the slot structure is preserved across the master swap.

6.3 Failure Mode

If the racks and the S7 master are power-cycled together, the ET 200L loses its SC configuration, the S7 master has nothing to download, and the SC I/O goes silent (no diagnostic, no SF LED). The cure is to repeat the live transfer from the S5 master.

7. Workaround 3 — Type File (.GSx) Installation Attempt

Engineers who want the type file path often try the following sequence. Document the failure explicitly so that the next engineer does not waste a day re-running it.

7.1 Procedure

1. Locate the ET 200L type file from a STEP 7 installation that pre-dates V5.4, or extract it from a legacy project that included the SC rack. The relevant files are SIE_8027.GSG (German) and its localized siblings.
2. Launch SIMATIC Manager > Options > Install HW Updates.
3. Point the installer at the directory containing the type file.
4. Observe the catalog log:

SIE_8027.GSG describes a KGP/ET 200L slave.
Slaves of this group based on GSD file (type file) are presently not supported.

5. Close the installer; the type file is rejected and the ET 200L catalog entry is unchanged.

7.2 Confirmed Working Versions

STEP 7 V5.1, V5.2, and V5.3 SPx have been observed in the field to install the type file and expose the SC sub-rack rows. If a legacy laptop with one of these versions is available, build a throwaway project, paste in the ET 200L-SC, configure the SC slots, save, archive the project, and use the paste-from-project method (Workaround 1) on the V5.5 target.

8. Step-by-Step: Building a Working ET200L-SC Configuration in STEP 7 5.5

Combining the three workarounds above, the practical end-to-end procedure that succeeds on a real migration is:

8.1 Build a Donor Project on a Legacy STEP 7 Version

1. Install STEP 7 V5.3 (or V5.1, V5.2) on an isolated laptop.
2. Create a new project with the same CPU family (S7-300 or S7-400) that will be the eventual master.
3. Open HW Config and add the ET 200L base block to the PROFIBUS master system at the target DP address.
4. Confirm that the TB16SC line and the A/B/C… SC module slots appear in the rack view. If they do not, install the ET 200L type file via Options > Install HW Updates; this version will accept it.
5. Insert each SC module into its slot. Set the I/O addresses to match the target wiring.
6. Save and compile. Archive the project as a .zip.

8.2 Transfer the Station to the STEP 7 V5.5 Project

1. Open the V5.5 target project in SIMATIC Manager.
2. Open HW Config on the destination station.
3. Paste the ET 200L station from the donor archive using the procedure in Section 5.2.
4. Re-verify the I/O addresses against the wiring diagram.
5. Compile and download the hardware configuration to the S7 master.

8.3 Commissioning with the Live Power Transfer

1. With the S5 master still in service and the racks powered, perform the live PROFIBUS connector swap described in Section 6.1.
2. Bring the S7 master online and verify PROFIBUS diagnostics (PLC > PROFIBUS > Diagnose) show every ET 200L station in OK state.
3. Force each SC output to ON and confirm the corresponding field device responds.

9. Verifying the SC I/O is Communicating

The key signal that the SC sub-rack has accepted the downloaded configuration is that the SC inputs read live field values on the very first cycle after the master swap. If the base block works but the SC inputs are flat, the SC slot mapping has not been written to the rack — repeat the live power transfer from a master that has a valid configuration, or re-paste the station from the donor project.

10. Migration Path Forward — STEP 7 V5.5, STEP 7 V5.6, and TIA Portal

The SC slot limitation is specific to STEP 7 V5.5 (and V5.4). For long-term support, the migration options are:

• STEP 7 V5.6 (last V5.x release): ships with extended catalog support and accepts the ET 200L type file without the SIE_8027.GSG rejection. Projects migrated from V5.5 retain all HW Config objects, including pasted ET 200L stations. This is the lowest-risk upgrade target for sites that must remain on PROFIBUS.
• TIA Portal (V16 and later): the ET 200L family is supported as a PROFIBUS DP device via the HSP (Hardware Support Package) for legacy DP slaves. The SC sub-rack is configured through the device view's slot editor. Re-derive the SC slot structure from the TIA Portal device view rather than pasting a STEP 7 V5.x station; the object model is not directly compatible.

For projects that must remain on STEP 7 V5.5 — typically because the master is a long-lifecycle S7-300 CPU that the customer is not yet ready to replace — the paste-from-donor approach (Section 5) is the only sustainable in-V5.5 technique. Document the donor project's GSD revision and type file version in the project header so that any future catalog update can be evaluated against the embedded configuration.

11. Troubleshooting Matrix

FAQ