Resolving SINUMERIK 840D STEP 7 V5.5 Upload-to-PG and Online Connection Errors

This technical reference documents the field-proven procedure for resolving the most common SINUMERIK 840D PLC online connection failures when the engineering workstation is running STEP 7 V5.5. The symptoms covered here are: upload-to-PG succeeds but Go Online returns no connection, the Accessible Nodes window reports the MPI/PROFIBUS node as unreachable, the Access Point of the Application field appears greyed-out, and any attempt to Download to Target returns the error Function not supported or Download to PLC not possible.

The 840D integrates an S7-300 class PLC (typically CPU 317-2DP for powerline, CPU 314C-2DP for the sl variant, or CPU 315-2 DP / 317-2 DP for older 840D powerline builds). The PLC is programmed from the STEP 7 V5.x SIMATIC Manager and is accessible via the NCU (Numeric Control Unit) on either MPI, PROFIBUS DP or Industrial Ethernet depending on the build state. Because the PLC firmware, HMI software, NCK software, and PLC user program are all version-coupled, the wrong combination of STEP 7, PLC Toolbox, and HMI version is the single largest source of upload/online errors. This article walks through the diagnosis, the software matrix, and the verified commissioning sequence.

1. Problem Statement and Reproduction Steps

The reported failure follows a deterministic sequence:

1. Engineer installs STEP 7 V5.5 (SPx) plus toolbox on a maintenance PC that did not ship with the machine.
2. Engineer installs an HMI version (for example V07.06) and a new HMI softkey to expose the PLC programming entry point.
3. Engineer connects an MPI cable (6ES7901-2BF00-0AA0 or PC-Adapter USB A2 6GK1571-1AA00) between the PG/PC and the 840D NCU X122 / X132 interface.
4. Engineer launches Upload Station to PG from SIMATIC Manager. Upload completes; the S7 program is read into the offline project.
5. Engineer clicks PLC → Go Online, PLC → Download, or PLC → Accessible Nodes. The operation either times out or returns a permission/protocol error.

The diagnostic signature is that Upload to PG uses the SINUMERIK Upload Station transport (NCK-NCU based, independent of STEP 7's online services), whereas Go Online, Accessible Nodes, and Download use the S7 Online Services (MPI/DP/ISO-on-TCP) which require the STEP 7 PLC Toolbox to be installed, the correct GSD/HW catalog to be present, and a configured Access Point of the Application.

2. SINUMERIK 840D PLC Architecture and Online Interfaces

The 840D powerline NCU contains three logical controllers that share the backplane and the PROFIBUS DP segment:

The PLC occupies a fixed PROFIBUS DP slave address. For the original 840D powerline this is DP address 2, for 840D sl it is DP address 3 unless the machine builder re-assigned it. When the engineering PC speaks to the wrong address, Accessible Nodes returns No nodes found rather than a permission error. Verify the bus address using HMI softkey Commissioning → Bus Diagnostics or by viewing the DIP switch S3 on the NCU module (rotary switch, range 0..15).

The transport protocols available between PG and NCU are:

• MPI 187.5 kbit/s — legacy path via X122 (840D powerline) or X122 (840D sl). Maximum bus length 50 m with no repeater.
• PROFIBUS DP 1.5 Mbit/s — X122/X132 with PROFIBUS terminators active at both ends of the segment.
• Ethernet / ISO-on-TCP — X130 port on 840D sl NCU 710.3B and newer. Requires CP 343-1 Lean / Advanced to be configured inside the PLC station.

3. Required Software Versions and Compatibility Matrix

Siemens releases the SINUMERIK 840D Add-On Toolboxes that bundle the correct SIMATIC hardware catalog (HW Config), the PLC basic program (GP.BSF), the system data blocks for the NCK-PLC interface (DB10, DB11, DB20, DB21..DB30), and the symbols file. Using STEP 7 without the matching toolbox causes:

• Hardware catalog empty for SINUMERIK entries.
• Symbolic I/O addresses unknown (V38000000, V380x0000, V39000000 ranges).
• Download blocked because the basic program blocks (OB1, OB100, OB102, FB1, FB2, FB3, FC22) differ from the runtime image.
• Online diagnosis not possible because the GSD file for the 840D NCU is not loaded.

The reference for the original poster is the PLC Toolbox V06.04.07 for an 840D with NCU 561/571 running SW 6.x or 7.x. The toolbox includes:

• STEP 7 Add-On (registers the SIMATIC Manager entry SINUMERIK 840D).
• PLC basic program archive GP840D_V06.04.07.arj.
• Hardware catalog with NCU 561, 571, 572, 573 and 611D drive entries.
• GSD file SIEM8110.GSD (for the NCU DP slave).
• Symbol file NC-VAR.SEQ for NC variables.

The PCU-Toolbox V2.4 (E) referenced by the original poster is the PCU 50.3 service tool and is not interchangeable with the PLC Toolbox. PCU-Toolbox configures the HMI/PCU image and base system software; it does not provide the STEP 7 SIMATIC components needed for online access.

4. Root Cause Analysis

Three root causes account for ~95 % of the 840D / STEP 7 V5.5 online errors seen in the field:

4.1 Missing or Wrong PLC Toolbox Add-On

Without the toolbox, STEP 7 V5.5 does not recognise the NCU as a valid DP slave. The Accessible Nodes scan returns nothing even when the bus wiring is correct and the NCU is in run. Confirmation path: in SIMATIC Manager, right-click the project, choose Add SIMATIC PC Station — if the SINUMERIK 840D template is absent, the toolbox is not installed.

4.2 PG/PC Interface Access Point Mis-configured

STEP 7 binds online services to a single Access Point of the Application (S7ONLINE for STEP 7 V5.x). If the access point references a different network adapter than the one physically connected to the 840D, all online calls time out. The Access Point field in the PG/PC Interface dialog will be greyed-out while STEP 7 is open; that is by design. Configure the access point with STEP 7 closed, or via Control Panel → Set PG/PC Interface.

4.3 HMI Version Skew / Wrong Softkey Bundle

The HMI V07.06 softkey created by the field engineer is an HMI-Advanced configuration item. The PLC toolbox matching it must be V07.06. A V06.04.07 toolbox paired with a V07.06 HMI causes the PLC basic program blocks (FB1, FB2, FB3, FB4, FC22, FC62, FC100) to mismatch the runtime image. STEP 7 will refuse the download with Online: Different block exists online even when the offline blocks are correct.

5. Installing the PLC Toolbox

1. Close SIMATIC Manager, S7-PCT, and any STEP 7 sub-tool. The installer (SETUP.EXE on the toolbox DVD) refuses to run while a STEP 7 process holds the registry hive.
2. Insert the toolbox DVD. Autorun presents the language selection. Confirm the detected STEP 7 base install (V5.5 in this case) is correct; the installer rejects mismatches.
3. Choose Complete installation to register both the SIMATIC components and the NC-VAR symbol table.
4. Restart Windows. The Siemens automation license manager (ALM) moves the toolbox license to the local license key or transfers it to a parallel license server.
5. Verify with Start → SIMATIC → Information about the Add-On Packages. The line 840D Add-On V06.04.07 installed must appear.

6. PG/PC Interface Configuration

The PG/PC interface is configured separately from the project and is global to the engineering user. Open Start → SIMATIC → STEP 7 → Set PG/PC Interface (or Control Panel → Set PG/PC Interface) and apply the following:

The address 0 is the reserved PG/PC address and must not collide with the NCU. If the project already used address 0 for a slave, change the PG to address 14 or 15. On a multi-segment bus, ensure the PC Adapter is connected directly to the NCU X122 (not the I/O rack), because the 840D powerline does not forward DP traffic across the backplane without a configured DP master in slot 3 of the rack.

7. Hardware Configuration Update

The PLC basic program block list must match the runtime. After installing the toolbox, refresh the HW catalog and update the offline configuration:

1. Open SIMATIC Manager and load the project that was produced by Upload Station to PG.
2. Double-click Hardware to open HW Config.
3. From the menu Options → Update Catalog. Wait for the dialog Catalog successfully updated.
4. From Options → Install HW Updates → Browse, navigate to the toolbox DVD or extracted ISO and select hwup840d.exe from the toolbox. Confirm with Install.
5. Restart HW Config. The SIMATIC 300 → SINUMERIK 840D catalog folder must now contain NCU 561 / 571 / 572 / 573 entries with the matching GSD references.
6. Right-click the rack and choose Properties. Verify the slot-2 PLC CPU matches what was uploaded (CPU 317-2DP for 840D, CPU 314C-2DP for 840D sl, CPU 315-2DP for legacy).
7. Save and Compile (Station → Save and Compile). The System Data container must regenerate without errors.

8. Establishing Online Connection

1. In SIMATIC Manager select the S7 Program node.
2. Click PLC → Go Online, or click PLC → Accessible Nodes to enumerate the bus.
3. The online view must report a target with the DP/MPI address assigned to the NCU (2 or 3). The diagnostic buffer is read by PLC → Diagnostic/Setting → Diagnostic Buffer.
4. Right-click any block and choose Monitor/Modify. The status flags in OB1 (cycle tick), OB82 (diagnostic interrupt), OB100 (warm restart), OB102 (cold restart) should be visible.

If Accessible Nodes shows the target but Go Online fails with Online: Cannot reach the partner, the cause is a mismatch between the offline CPU type and the online CPU type. Re-upload to PG, open HW Config, and double-click the rack to refresh.

9. Upload-to-PG Procedure and Archive Format

The Upload Station to PG operation pulls the PLC user program through the SINUMERIK Upload Station, which proxies the S7 protocol over the NCK-PROFIBOARD interface. The output is a SIMATIC archive file with the extension *.arj or, on newer toolbox releases, *.s7p. The archived project contains:

• Blocks container (OB, FB, FC, DB, SDB, SFB, SFC).
• Source files container (STL sources if S7-SCL is enabled).
• Symbol table (exported as ASCII for the NCK interface symbols).
• System data (HW Config snapshot).
• PLC basic program library (FB1..FB7, FC22..FC200, FC1000).

The original poster's symptom (upload succeeds, online fails) confirms that the Upload Station path is healthy but the S7 Online path is blocked. The remediation order is therefore toolbox install → PG/PC interface → HW Config update → Go Online retest.

10. Download Restrictions and Password Protection

The 840D PLC has password classes defined in STEP 7 → PLC → Access Protection (CPU properties → Protection tab):

Many 840D machines ship with level 2 protection enabled so that the OEM can prevent the end user from modifying the safety-relevant FC62 (emergency stop) and FC22 (NCK-PLC handshake) blocks. Download to Target will fail with Cannot download to target - protection violation until the matching password is entered under PLC → Access Protection → Enter Password. This is independent of the toolbox and Access Point configuration and is a frequent false-positive cause of online works, download fails.

If the password is unknown, the procedure to recover programming access is:

1. Back up the current project with Upload Station to PG.
2. Insert the toolbox DVD and execute Tools → Reset Password (only available with toolbox V06.04.07 or later).
3. The PLC is reset to protection level 1 and the password is cleared from the CPU memory. A cold restart (OB102) is triggered automatically.
4. Reload the saved project, recompile HW Config, and download the corrected SDBs.

11. Verification and Commissioning Checklist

Run the following checks after the toolbox and PG/PC interface are corrected:

1. Accessible Nodes scan: Reports the NCU at the expected DP/MPI address with CPU type CPU 31x-2 DP.
2. Online diagnosis buffer: No entries of type Communication error or Parameter assignment error in the last 24 h.
3. Monitor on OB1: Tick bit M0.0 visible, DB2 interface flags match the HMI screen state.
4. Force on a test flag: M100.0 can be forced and the change is visible in the HMI PLC Diagnosis view.
5. Download test block: Insert a FC99 "Hello World" STL block, download, verify execution in online monitor.
6. Upload verification: Re-upload to PG, diff the new archive against the source archive — only the test FC99 should differ.
7. HMI lock check: Confirm that the HMI softkey PLC → Stop is greyed-out in operator mode (OEM protection).

12. Reference Documentation

• SINUMERIK 840D/840D sl PLC Basic Program List Manual
• SINUMERIK 840D Commissioning Manual (NCK / PLC / Drive)
• SINUMERIK 840D Toolbox V06.04.07 Installation Notes
• STEP 7 V5.5 SP4 Online Help — Set PG/PC Interface
• SINUMERIK 840D sl HMI-Advanced V2.6 SP1 Manual
• SINUMERIK 840D PLC Access Protection and Password Handling
• SINUMERIK Operator Components & Engineering Overview