SINUMERIK 840D: Restoring Missing G500-G599 Frames After Backup

SINUMERIK 840D: Restoring Missing G500-G599 User Frames After a Backup Restore

After reloading a series commissioning archive on a SINUMERIK 840D / 840D sl, operators frequently observe that only G54, G55, G56, G57, and G500 appear in the offset/work offset list, while the extended G501 to G599 settable frames have disappeared from the HMI. The machine continues to run, kinematics behave normally, and the NCK does not report a clear alarm, but every part program that referenced the higher frame numbers now fails with 14800 "Channel %1 wrong checksum for correctable block %2" or with a frame-not-found alarm at block search. This article documents the root cause in machine data MD18601 $MN_MM_NUM_GLOBAL_USER_FRAMES, the family of related MM_-prefixed machine data that governs settable frame count, the correct procedure to expose the missing frames after a backup restore, and the field-proven verification checks.

1. Problem Definition

The archive restore reloaded every NC machine data block and every part-program/frame file from the backup, but the HMI still showed only five entries. After a manual check, MD18601 was discovered to be set to 1, which is far below the values Siemens uses for any production 840D. The user increased it to 5, expecting the standard G54..G57 + G500 mapping, but the offset list remained unchanged. Only after copying the complete data set from a sister machine did the offset list recover.

2. Root Cause: MD18601 $MN_MM_NUM_GLOBAL_USER_FRAMES

The settable frame table size is governed by one global machine data, supported by a family of related MM_-prefixed parameters:

MD18601 $MN_MM_NUM_GLOBAL_USER_FRAMES
   = 5    ; G500 plus G54..G57    (default for many 840D shipments)
   = 50   ; G500 plus G54..G57 and G501..G547
   = 100  ; G500 plus G54..G57 and G501..G599
   = 0    ; No settable frames (G500 still exists as the "deselect" frame)
   = 1..n ; non-standard value often produced by corrupted/partial archive

The first five frame numbers are fixed by the language scope (G54 through G57) plus the deselect frame G500. Any additional frame that the application uses (G501 through G599) is allocated dynamically by the NCK up to the value of MM_NUM_GLOBAL_USER_FRAMES. If the value is too small, the NCK never creates the runtime data structures for the higher frames; a backup/restore cannot resurrect them, because the destination control literally has no place to store them.

3. Family of Frame-Governing Machine Data

Settable frames are not the only memory structures affected by MD18601. The following machine data are typically reviewed together, because the HMI uses the maximum of these for display purposes and the archive restore must set them consistently:

The per-channel parameters (MD28080, MD28081) exist because Siemens historically differentiated between NCU-global and channel-local frames. On a modern 840D sl with one NCU, the values should be identical to the global ones to keep the HMI consistent. If MD28080 is 5 but MD18601 is 100, the HMI will show 100 entries globally but only 5 per channel in the offset detail view, and operators will still perceive a "missing" frame list.

4. Prerequisites for Recovery

1. Operator access level Manufacturer (password level 3) for changing MM_ machine data, or Service level (password level 2) if the access bits were pre-configured by the OEM.
2. A complete, verified series commissioning backup of a known-good sister machine with the same NCU software version.
3. Empty CF card slot or USB stick with at least 4 GB free, formatted in FAT32.
4. For NCK Power On: ability to bring the machine to a safe state (open covers, retracted axes, no part in the chuck).
5. HMI version compatibility: the source archive must be from an HMI software version that matches the destination (e.g., HMI Pro sl 4.8 SP3 cannot read an HMI Pro sl 5.x archive).
6. Documentation of any customer-specific NC macros or compile cycles; these are not always inside the standard *.arc and must be backed up separately.

5. Step-by-Step Recovery Procedure

5.1 Inspect the Current Setting

1. Switch to area Startup > Machine Data.
2. Open the search dialog and enter 18601.
3. If the search returns no row, the current display filter is hiding it. Press the softkey Options > Filter and select Cancel all filters (or "Show all machine data") so that all expert parameters become visible.
4. Note the current value of MD18601 $MN_MM_NUM_GLOBAL_USER_FRAMES and record it for the rollback step.
5. Repeat for MD18602, MD18603, MD28080, MD28081.

5.2 Determine the Required Value

Open the part program of a representative production cycle on the original machine before the backup was made, or on the sister machine that has the same program set, and search for any G5 followed by a digit:

; example program excerpt
N10 G54 G90 G17
N20 G501 ; fixture offset A
N30 G502 ; fixture offset B
...
N540 G599 ; last used extended frame

The highest G5xx number referenced anywhere in the active program set defines the minimum value for MD18601. Round up to the nearest "nice" value (5, 50, or 100). Siemens recommends 100 for any mill or turning cell that uses multiple fixtures, tombstones, or pallet systems.

5.3 Modify MD18601 and Relatives

1. Enter 100 in MD18601 $MN_MM_NUM_GLOBAL_USER_FRAMES.
2. Enter 1 in MD18603 $MN_MM_NUM_GLOBAL_BASE_FRAMES if the application uses only the default base frame; increase to 16 for multi-base applications.
3. Enter 0 in MD18602 $MN_MM_NUM_GLOBAL_GUARD_FRAMES unless safety has configured guard frames.
4. Set MD28080 $MC_MM_NUM_USER_FRAMES to the same value (100) for every channel.
5. Set MD28081 $MC_MM_NUM_BASE_FRAMES to match MD18603 in every channel.

5.4 Apply the Change (NCK Power On Required)

1. Bring the machine to a safe state (all axes referenced, no part in the working area, doors closed).
2. Switch the NCK to commissioning mode via PLC signal DB10.DBX0.1 = 1 if your machine configuration requires it for parameter changes.
3. Perform NCK Power On: Startup > NCK > NCK Reset (po), confirm the prompt.
4. Wait for the NCK to come back ready (status field on HMI shows "Run", not "Stop" or "Boot").
5. Open the offset page: Offset > Work Offsets (G54..G599). The list must now show G500 plus G501 through G599.

5.5 Reload Frames if Missing

Even with MD18601 set correctly, frame values stored under G501..G599 that came from the backup are only valid if the source archive was made with the same MD18601 value. If the values appear blank or zero:

1. Restore the commissioning archive once more, but this time use the matching sister-machine archive that has MD18601 = 100.
2. After restore, perform an NCK Power On again.
3. Verify that the frame contents are now populated. If not, the source archive itself was made on a machine with a smaller value, and the frames must be re-entered manually or by reading them from a separate work-offset backup (*.bck or *.wop).

6. Verification

Run the following checks after the recovery procedure:

7. Backup Archive Considerations

Series commissioning archives (*.arc) created on a SINUMERIK 840D always contain the active machine data values. However, the archive format encodes only the differential between the OEM-default set and the current values. If the destination machine has a different NCU software version, some MM_ parameters may not be transferable. Use these rules:

• Always restore to a target NCU whose NCK software (e.g., 06.07.42) is greater than or equal to the source NCK software. Downgrading an archive is not supported.
• Compile cycles (CC) are stored in a separate binary inside the archive; if the CC license key was not transferred, the CC-driven frames (e.g., 5-axis transformations stored as G5xx values) will appear empty.
• If the source archive was created with MD18601 = 5, it will not retroactively populate G501..G599 on the destination, even when MD18601 is later increased. The frames have to be entered manually.
• Verify the archive integrity by opening it on a PC with the SINUMERIK Operate Viewer (if available) and checking the file NCK.MD for the MD18601 line.

8. Display Filter vs. True Absence

Operators sometimes report "frames disappeared" when in fact they are hidden by the HMI filter. Distinguish between the two cases:

The HMI softkey path varies by HMI generation:

• HMI Pro sl (SINUMERIK Operate): Offset > Work Offsets > G5xx > Options > Filter > Show all.
• HMI Advanced: Tools > Work Offsets > Options > Display > Show all frames.
• HMI Embedded: Settings > Display > Frames > All.

9. Reference: ISO Dialect G Code vs. Siemens G Code

SINUMERIK 840D supports both Siemens dialect and ISO dialect G code. The programming manual explicitly states: "Only ISO Dialect G codes can be programmed, not Siemens G codes" when the controller is configured in ISO Turning mode (G code system B or C). In ISO mode, G500 retains the same meaning (cancel all settable frames), but the extended G501..G599 still depend on MD18601. The DISPLOF procedure-call modifier "freezes the block display at the call block; the G code display remains in" its current state, which is useful for verifying the active frame inside a cycle without scrolling.

10. Troubleshooting Matrix

11. Field-Proven Caveats

• Increasing MD18601 from 5 to 100 on an active production machine without an NCK Power On causes the HMI to show "ghost" entries that disappear after the next restart, leading to operator confusion. Always perform NCK Power On in a planned maintenance window.
• On 840D sl with HMI Pro sl 5.x and the new compile cycle kinToolbox, some frames are reserved by name (e.g., G595 through G599). Adjust the application to use a contiguous range below the reserved zone to avoid clashes.
• Some OEMs shrink MD18601 to 5 in the factory default archive to reduce boot time on legacy NCUs. Any sister-machine archive must be from a machine with the same OEM build, otherwise the restore will silently reset the parameter.
• Frame data persisted via _N_SETUP_DIR is stored in a binary structure whose length is determined at NCK startup. If you change MD18601 downward, the truncated frames will be lost. Always back up _N_SETUP_DIR before decreasing any MM_ parameter.

12. Quick Reference: Related Alarms

FAQ