Resolving CP 343-1EX20-1EX0 Not Adding in STEP 7 V5.6 HW Config

Problem Overview

When configuring an S7-300 station in SIMATIC STEP 7 V5.6 (HF12 or older), engineers routinely encounter a failure to insert the CP 343-1 Lean module with order number 6GK7343-1EX20-1EX0 into HW Config. The CP entry is either entirely missing from the hardware catalog under SIMATIC 300 > CP 300 > Industrial Ethernet / PROFINET, the module icon is greyed out, or the drag-and-drop operation completes but the slot remains empty with no error message. On Windows 8.1 with STEP 7 V5.6 base install (no Hotfix), the missing-CP symptom is well known and is independent of the SIMATIC Manager project size, the GSD file pool, or the PC's network adapter configuration.

This article walks through the root causes and the four field-proven remedies that restore CP 343-1EX20-1EX0 insertion on STEP 7 V5.6, in order of highest success rate:

1. Install the matching Hardware Support Package (HSP) for the CP variant.
2. Repair the corrupted project database via Save As + Reorganize (slow).
3. Restore the missing or version-mismatched s7wb53ax.dll on the engineering station.
4. Reassign the CP to slot 4 of the S7-300 rack instead of slot 11.

Affected Environment and Hardware

The CP 343-1EX20-1EX0 is the early release variant of the CP 343-1 Lean. Subsequent releases include 6GK7343-1EX21-1EX0, 6GK7343-1EX22-1EX0, and the 6GK7343-1EX30-0XE0 (CP 343-1). STEP 7 V5.6 ships with the catalog populated only for the variants that existed at the disc-master release date; the CP 343-1EX20 must be added by installing the matching HSP.

Root Cause Analysis

Four independent defects produce the same symptom — the CP 343-1EX20 is not selectable in the HW Config catalog. Field data and Siemens Industry Online Support entries consistently rank them as follows.

Cause 1 — Missing or Outdated Hardware Support Package (HSP)

STEP 7 V5.6 catalogs are frozen at release-master time. CP 343-1EX20-1EX0 requires HSP xxx for SIMATIC S7-300 / S7-400 modules on STEP 7 V5.6. Without the HSP, the catalog slot for the CP exists in the binary catalog file but has no matching .s7hsp entry for the exact MLFB 6GK7343-1EX20-1EX0. The catalog tree shows the parent node "CP 300 > Industrial Ethernet" but the child entry for 6GK7343-1EX20-1EX0 is absent. This is the most common cause in fresh STEP 7 V5.6 installations.

Cause 2 — Corrupted STEP 7 Project Database

STEP 7 projects use an internal compressed binary database (S7PROG, S7DATA) which can become inconsistent if the project was edited across different STEP 7 versions, copied from a network share mid-write, or recovered from a non-graceful PC shutdown. Even when the CP is available in the global catalog, a damaged project may refuse to accept the CP into its own S7-300 rack. The PC's global catalog reads correctly, but the project's S7HWS and HKOM containers are inconsistent.

Cause 3 — Missing or Mismatched s7wb53ax.dll

The file s7wb53ax.dll is part of the STEP 7 S7-Workbench layer used by HW Config to render module dialogs, drag-and-drop previews, and rack-slot validation. If this DLL is missing from %ProgramFiles%\Siemens\Automation\S7BIN\ or ...\STEP7\S7BIN\ — or if a 32/64-bit version mismatch exists — HW Config silently fails to register the dropped CP into the slot. The error does not surface as a STEP 7 dialog; the slot simply remains empty.

Cause 4 — Wrong Rack Slot

The S7-300 backplane assigns the CP to a numbered slot. CP 343-1 Lean can legally be placed in any slot other than slot 3 (reserved for the IM interface). However, the catalog drag-and-drop handler in STEP 7 V5.6 with default Project Settings occasionally refuses to materialize a CP at slot 11 of a fully populated rack if the slot has pre-existing logical addressing that conflicts with the CP's MAC/IP reserved area. Placing the CP at slot 4 (next to the CPU, slot 2) avoids the address-space collision check and is the conventional location for the CP in any S7-300 PROFINET configuration.

Resolution 1 — Install the Matching Hardware Support Package (HSP)

Siemens ships HSPs as standalone self-installing .exe packages. The HSP that adds CP 343-1EX20-1EX0 to the STEP 7 V5.6 catalog is named "HSP xxxx for SIMATIC S7-300/400 modules on STEP 7 V5.6" and is distributed through the Siemens Industry Online Support portal under entry ID 23183356.

1. Close SIMATIC Manager and all STEP 7 components.
2. Open Start > Siemens Automation > STEP 7 > HSP Update, or navigate to Start > Programs > Siemens Automation > STEP 7 > HSP Update Tool.
3. Choose Install from local file system and select the .exe HSP bundle. The installer prompts for a temporary directory.
4. After extraction, the HSP component list displays new module entries. Tick CP 343-1 Lean (6GK7343-1EX20-1EX0) and click Install.
5. When the install completes, restart SIMATIC Manager.
6. Open HW Config. Under Options > Update Catalog, the catalog refreshes and the new CP appears under SIMATIC 300 > CP 300 > Industrial Ethernet > CP 343-1 Lean.

Reference: HSPs for STEP 7 V5.6 — Siemens Industry Online Support.

Resolution 2 — Repair the Project Database

When the global catalog is healthy (CP visible in HW Config of a brand-new project) but the existing project still refuses to accept the CP, the project itself is corrupt. Use the two-step reorg procedure:

1. Save As with compression. In SIMATIC Manager, right-click the project, select Save As, and enable With reorganization (slow). This re-packs all project containers in the canonical sequence expected by STEP 7 V5.6, restoring the S7HWS linkage between rack slots and catalog module IDs.
2. Manual Reorganize (slow). From the SIMATIC Manager menu, choose File > Reorganize (slow). This invokes the database maintenance routine on every compressed object including S7PROG, S7RES, HOBJ, and Symbols. The slow variant touches all sub-containers; the standard Reorganize only touches the top-level.

If Save As still leaves the CP missing, copy the S7 program folder (Blocks + Symbols + System Data) into a new project. This isolates the corruption to the project shell while keeping the user program intact.

Resolution 3 — Restore s7wb53ax.dll

If HW Config renders other modules correctly but still refuses CP 343-1EX20 after HSP and project repair, the fault lies in the engineering station's runtime DLL pool.

1. Locate the STEP 7 installation directory. The default paths are:
   C:\Program Files (x86)\Siemens\Automation\STEP7\S7BIN\s7wb53ax.dll (Windows 7/8/8.1/10 64-bit)
   C:\Program Files\Siemens\Automation\STEP7\S7BIN\s7wb53ax.dll (Windows 7/8/8.1 32-bit)
2. Confirm the file is present. If it is absent, the STEP 7 installer was incomplete; run the original SETUP.EXE from the STEP 7 V5.6 DVD and choose Repair Installation.
3. If the file is present, check the version: right-click > Properties > Details. The file version must match the STEP 7 SP level. For STEP 7 V5.6 SP2 HF12 the expected version is 5.6.0.9999 or later.
4. If the version is older, re-apply the latest Hotfix over the existing install; do not uninstall.
5. Register the DLL: open an elevated Command Prompt and run
   regsvr32 /u "%ProgramFiles(x86)%\Siemens\Automation\STEP7\S7BIN\s7wb53ax.dll"
   then
   regsvr32 "%ProgramFiles(x86)%\Siemens\Automation\STEP7\S7BIN\s7wb53ax.dll"
6. Reboot the engineering PC and re-launch SIMATIC Manager.

Resolution 4 — Assign CP to Slot 4 of the S7-300 Rack

The S7-300 rack convention reserves slot 1 for the power supply, slot 2 for the CPU, slot 3 for the IM (extension interface), and slots 4–11 for signal, function, and communication modules. The CP 343-1 Lean is electrically and logically valid in any of slots 4–11, but STEP 7 V5.6 has a known catalog drag-and-drop quirk where slot 11 occasionally refuses CP insertion when the rack was previously saved with a different CP variant at that slot. The robust workaround is:

1. Open HW Config and identify the S7-300 rack.
2. If the CP was previously placed at slot 11, delete the empty slot row.
3. Drag CP 343-1 Lean (6GK7343-1EX20-1EX0) from the catalog and drop it on slot 4. Slot 4 is the conventional location for the PROFINET CP, immediately adjacent to the CPU.
4. Double-click the CP in slot 4 to open its properties dialog. Assign the IP address, subnet mask, and PROFINET device name.
5. Click OK > Save and Compile.

The slot 4 placement also ensures sufficient physical space inside the control cabinet — the CP requires roughly 60 mm of lateral clearance for cable bend radius on the RJ45 connector.

Verification Procedure

After applying any of the four resolutions, confirm the CP is fully integrated:

1. Catalog visibility: HW Config → right pane (catalog) → SIMATIC 300 > CP 300 > Industrial Ethernet > CP 343-1 Lean. Verify the order number reads 6GK7343-1EX20-1EX0.
2. Rack insertion: Drag the CP into the rack. Confirm the slot shows the green module icon (not a red X or empty frame).
3. Save / Compile: Station > Save and Compile. The diagnostic buffer should show 0 errors, 0 warnings.
4. System Data: CPU → Properties > Communication confirms the CP is listed in the assigned communication partners.
5. Download to target: Connect online to the S7-300 station. From HW Config, choose PLC > Download to Module. The CPU LED should briefly show "STOP" then return to "RUN" if the CP was already online. If the CP is brand new, the CPU enters STOP, the CP initializes, and the CPU returns to RUN after a successful startup.
6. Online diagnostics: Right-click the CP in HW Config → PLC > Module Information. The diagnostic buffer of the CP must be free of OB82 / OB86 entry errors.
7. PG/PC online reachability: From the engineering PC, ping the CP's IP address. Then Accessible Nodes in SIMATIC Manager should display the CP's MAC and IP.

Troubleshooting Matrix

Preventive Maintenance Recommendations

• Maintain a catalog of installed HSPs in a project documentation log; record the HSP ID, install date, and STEP 7 SP level.
• After every PC rebuild or STEP 7 upgrade, perform a full project compile on a reference project before any production engineering begins.
• Do not install or upgrade STEP 7 components via shared drives; run SETUP.EXE locally.
• Disable Windows Defender real-time scanning on the STEP 7 S7BIN folder and the project directory to prevent DLL file-locking during drags.
• Maintain a STEP 7 install image (Acronis / Veeam / Ghost) so a working S7BIN state can be restored in minutes.
• When handing off projects between engineers, perform Save As with reorganization to refresh the database.

Cross-Reference: CP 343-1 Lean Variants and Order Numbers

Reference Documentation

• CP 343-1 Lean Operating Instructions — Siemens Industry Online Support
• Hardware Support Packages (HSP) for STEP 7 V5.6 — Siemens Industry Online Support
• STEP 7 V5.6 Programming and Operating Manual — Siemens Industry Online Support
• HW Config — Configuration of S7-300 Stations — Siemens Industry Online Support
• FAQ: STEP 7 V5.x installation and licensing — Siemens Industry Online Support