Sinumerik 840D MCP Flashing: Resolving PLC 200000/200001 Errors

Sinumerik 840D MCP Flashing: Resolving PLC 200000/200001 Errors

A Sinumerik 840D control that powers up with all Machine Control Panel (MCP) keys flashing and a "PLC not alive" alarm indicates the integrated PLC has either failed to start, lost communication with the HMI/NCU, or is executing an incompatible program. The two alarm codes that most commonly appear in this condition are 200000 (PLC sign-of-life monitoring) and 200001 (PLC has not started up). This reference covers the diagnostic path, the NCU switch-based reset procedures, archive compatibility issues, and the recovery options when no working PLC backup is available.

1. Problem Summary

The NCU displaying 6 is a useful first signal: it confirms the PLC submodule is reachable and the firmware has booted into the PLC stop state, but no user program is cycling. Without a running OB1, the PLC watchdog times out, MCP communication is never established, and the panel defaults to a flashing-key fault indication.

2. Hardware Identification

Before executing any recovery procedure, record the part numbers of every module on the PROFIBUS/Ethernet ring. The part numbers determine which firmware branch, archive format, and PLC project can be loaded.

Confirm the NCU variant on the type plate. The 0BB21 designation places this in the NCU 57x.5 family. Cross-reference the ordering designation against the official Sinumerik 840D sl NCU configuration manual to verify the matching PLC firmware version that the archive must contain.

3. Alarm Code Definitions

Alarm 200000 — PLC Sign-of-Life Monitoring

This alarm is raised by the NCK when the integrated PLC fails to refresh the sign-of-life counter within the configured monitoring time. Typical triggers:

• PLC OB1 cycle time exceeds the sign-of-life window (default 300 ms).
• PLC program halted or in stop mode.
• Archive loaded with mismatched hardware configuration — PLC starts but immediately halts on a peripheral access error.
• Corrupted PLC project: symbol table present but code blocks invalid.

Alarm 200001 — PLC Has Not Started Up

This alarm appears when the PLC reports it never reached the run state after NC power-up. Typical triggers:

• NC/PLC general reset was performed (S4 sequence) and no project was reloaded.
• Archive was loaded but contained an empty PLC container.
• PLC firmware does not match the NCU boot loader version.

4. Root Cause Analysis

The most common root cause for a used Sinumerik 840D with flashing MCP keys and alarm 200000/200001 is a backup-archive mismatch. The PLC archive stored on the internal HDD was generated against a different machine configuration (different NCK version, different MCP variant, different bus topology, or a different machine tool builder OEM project). Even when the archive loads without an explicit error, the resulting PLC project either:

1. References HW Config I/O addresses that do not exist on this physical machine, or
2. Calls FB/FC blocks that were OEM-encrypted or compiled with a different Step 7 version, or
3. Targets a PLC firmware newer than the submodule's runtime supports.

When any of these conditions is met, the PLC halts within the first cycle and the sign-of-life counter is never refreshed. The NCK raises 200000 within the monitoring window. The MCP, which only receives pre-mapped I/O from the PLC, can see no valid input image and enters its fault state: all keys flash.

5. NCU Switch-Based Reset Procedures

The NCU has two rotary switches accessible from the front panel: S3 (NC reset / general reset) and S4 (PLC reset / PLC general reset). Always power-cycle the NCU after changing either switch and wait for the 7-segment display to settle before re-evaluating.

S3 Switch — NC Reset and General Reset

Procedure for NC reset:

1. Set S3 to position 1.
2. Press and hold the NCU reset button until the 7-segment display blanks.
3. Release. The NCU reboots. NCK restarts, PLC remains in its last state.
4. Return S3 to 0 after the cycle completes.

S4 Switch — PLC Reset and PLC General Reset

The PLC reset is performed by rotating S4 through a defined sequence rather than a single position. The most commonly cited sequence is the 2-3-2 toggle for PLC general reset, which clears all PLC user data including blocks, retentive flags, and the system data blocks.

PLC general reset sequence (2-3-2):

1. Set S4 to position 2, wait until the 7-segment display reflects PLC activity.
2. Set S4 to position 3 (general reset position), wait several seconds for the PLC to clear its memory.
3. Return S4 to position 2 to confirm and trigger the erase cycle.
4. Power-cycle the NCU. The PLC is now empty.

After this sequence, alarm 200001 is the expected state: the PLC has been cleared and is waiting for a project to be loaded. This is the correct state to begin a controlled archive load.

6. PCMCIA Card Considerations

The PCMCIA card slot on the NCU accepts a CompactFlash-formatted Siemens card that contains the boot image, optionally the PLC runtime, and is also used to transfer series commissioning archives (*.arc) into the system. The two failure modes commonly seen with replaced PCMCIA cards are:

1. Card was always defective: The card was purchased new but never tested. It may have been formatted with an incompatible filesystem, or it may be a non-Siemens CF adapter without the proper card information (CFI) block. Symptom: the NCU cannot read archives, or the boot sequence hangs.
2. Card was working, system failed: The card was functional, but a configuration change elsewhere caused the failure. Symptom: alarm 200000 appears despite an identical mechanical and electrical setup.

To isolate the PCMCIA card as the root cause:

• Boot the NCU and access the Service menu (key > on MMC 103).
• Navigate to Commissioning > PCMCIA and verify the card is detected.
• Check the card's file system: archives on the card must reside in a directory the HMI can index, and the file types must match the NCK build (e.g. archive *.arc for series commissioning, *.dsf for data set files).

If the card is not recognized, attempt to read it on a separate PC using a CF-to-USB adapter. The filesystem must be FAT16 with a specific cluster size. Siemens documentation lists the supported card types and the maximum capacity for each NCU variant.

7. Archive Compatibility

An archive that loads successfully on one Sinumerik 840D is not guaranteed to load on another. The compatibility matrix is governed by:

For used machines where the original archives are 15+ years old, the most likely incompatibility is in the drive data block. Older 840D systems used SIMODRIVE 611 digital; newer 840D sl systems use SINAMICS S120. A drive block from one family on the other family produces an immediate PLC halt.

Verifying Archive Validity Without Loading

Before performing a PLC general reset, evaluate every candidate archive on the HDD:

1. Insert the PCMCIA card or navigate to the HDD archive directory via the Service menu.
2. Open each *.arc and inspect the header. The header contains the source NCU part number, NCK version, and the date the archive was generated.
3. Match the source NCU part number to the target NCU part number 6FC5357-0BB21-0AE0. If they differ, the archive is a candidate for PLC only — do not load NCK data from it.

8. Step-by-Step Recovery Procedure

Use the following ordered procedure to move from the fault state to a clean running system. The procedure assumes the NCU has been confirmed reachable, the PCMCIA card is recognized, and at least one candidate archive is available on the internal HDD or the card.

Prerequisites

• PCMCIA card recognized by the NCU.
• At least one *.arc on the internal HDD or PCMCIA card.
• Access to the NCU front panel switches S3 and S4.
• 24 V DC supply stable (no undervoltage events during boot).

Procedure

1. Power down the NCU and remove the PCMCIA card.
2. Set S4 to the 2-3-2 sequence to clear all PLC data. Power-cycle to apply.
3. Set S3 to position 1, press reset. Wait for the NCK to complete the restart. The 7-segment display will cycle through the boot states and settle on 6 (PLC stop).
4. Return S3 to 0.
5. Insert the PCMCIA card. Power-cycle if it was not already inserted before the PLC reset.
6. Navigate on the MMC 103 to Commissioning > Series Commissioning > Read Archive. Select the most compatible *.arc from the list.
7. Confirm the restore. The NCK will load first, then the PLC, then the HMI data. The process takes 2 to 10 minutes depending on archive size.
8. Wait for the HMI to display the channel reset or operating area screen without active alarms.
9. Power-cycle the NCU one more time to confirm the loaded configuration is persistent across a clean boot.

Verification

• The 7-segment display on the NCU shows a steady 6 (PLC stop) or transitions to 0 if the PLC is configured to auto-run.
• The MMC 103 shows the standard operating area with no 200000/200001 alarm in the alarm bar.
• The MCP keys no longer flash. Pressing a key generates a corresponding input in the PLC online monitor (verify via Step 7 or the PLC variable view in the HMI).

9. When No Compatible Archive Exists

If every archive on the HDD is incompatible and the original machine tool builder (MTB) cannot supply a backup, the PLC must be redeveloped. This is the worst case and is not trivial: a complete PLC program for a milling or turning machine can range from a few hundred to several thousand network segments, including axis handshaking, tool changer logic, spindle control, coolant, hydraulics, and safety interlocks.

Options for Recovery Without an Archive

1. Source a ghost image from a similar machine. If another machine with identical NCU part number and similar configuration exists in the plant, clone its archive. Match the part number, the MCP variant, and the drive configuration exactly. This is the only fast path to a working system.
2. Obtain a tool box CD from the MTB. Some machine builders ship a "tool box" CD with the project source, including the STL/SCL source of the PLC program, the HW Config, and the NC machine data. The PLC project can be reloaded into Step 7 and recompiled against the current NCU firmware.
3. Engage the Siemens regional service center. The service center can recover an MTB-specific backup if the machine was commissioned through Siemens and the backup was registered in the Siemens commissioning database. They can also deploy a field engineer to recreate the PLC project from the machine's I/O list and electrical drawings.
4. Redesign the PLC. From the machine's electrical schematics, build a new HW Config and PLC program. This is a multi-week effort and requires the original machine documentation, the axis parameter list, and the I/O wiring list.

10. Diagnostic Cross-Check With Step 7

If a programming PC with Simatic Step 7 is available, attach it to the NCU's Ethernet port (X127 service interface) and read the PLC diagnostic buffer directly. The diagnostic buffer records the last fatal error before the PLC halted and is the most reliable way to identify the exact incompatibility.

Procedure:

1. Connect the programming PC to X127 with a standard Ethernet cable. The default IP for X127 is 192.168.215.1; the programming PC must be set to the 192.168.215.x subnet.
2. Open Step 7 Manager, select PLC > Accessible Nodes. The NCU should appear in the browse list.
3. Open the online view and select PLC > Diagnostic/Setting > Diagnostic Buffer.
4. Read the most recent event. Common entries after an archive mismatch are OB not loaded, IO access error, or block version conflict.

The diagnostic buffer will resolve the ambiguity between "archive invalid" (PLC refused to start) and "archive valid but incompatible with hardware" (PLC started, ran one cycle, and halted on I/O access). The recovery path is the same — a compatible archive — but the root cause is more clearly documented for the MTB engagement.

11. Preventing the Condition on Refurbished Machines

For any used Sinumerik 840D being recommissioned:

1. Capture a fresh series commissioning archive from the machine as it arrives, before any maintenance or restart attempts. This is the baseline.
2. Document the NCK version on the HMI start-up screen and the PLC firmware version from the PLC online view. Store these in the machine file.
3. Verify the PCMCIA card on a separate PC before relying on it. Confirm the directory structure and file sizes match the original Siemens card image.
4. Never delete the existing archives on the internal HDD until the machine is fully commissioned and a new, validated archive has been stored.

12. Frequently Asked Questions