Resolving SINUMERIK 840D Alarm 12550 _C97_NR Not Defined

Overview

SINUMERIK 840D controllers emit alarm 12550 ("Channel %1 Block %2 identifier %3 not defined or option not installed") when a defined GUD, macro, LUD, or program name is referenced in an NC block but is not present in the active scope. On a lathe retrofit running Cycle 95 / CYCLE97 thread-cutting, the alarm typically points at the channel-global array _C97_NR[11] declared in GUD7.DEF. The cycle cannot resolve a spindle-to-machine-axis mapping, so downstream calls into _C97_NR[n] fail with 12550 at NC-Start. This reference covers the diagnostic path for that specific failure, the machine-data checks that underpin it, and the recovery sequence for restoring CYCLE95 / CYCLE97 operation without reloading the entire cycle pack.

Siemens documents the general meaning of alarm 12550 in the SINUMERIK MC alarms catalog (SINUMERIK 840D sl / ONE). The catalog entry confirms that the alarm fires when a definable identifier (macro, GUD, LUD, program name, or program block) is referenced before it is defined, or when an option bit required for that identifier is not installed. The remediation logic described below resolves the most common field cases of the _C97_NR variant on 840DE retrofit hardware.

Alarm 12550 Reference

Per the Siemens alarms catalog, the 12550 family fires only on identifiers that should exist; it is not an MD validity check. The check is performed by the interpreter against the symbol table populated at NCK power-on and after any explicit GUD reload. If the symbol exists but the value the cycle reads is 0 or the array element is empty (REP of the wrong default), the alarm will still appear, because the cycle passes the empty element back to a higher-level statement that calls it without first verifying validity.

Hardware and Software Environment

Documented from a real 840DE retrofit case (lathe X/Z spindle, threading CYCLE95 / CYCLE97):

The cycle file shown in the source contains the standard header banner ;VERSION: 06.05.14.00 Dec 07, 2004 while the loaded standard cycles on the controller are 06.04.21. Mismatched cycle/DEF versions are a frequent retrofit symptom: the user copies a newer CYCLE97.SPF from a development pack onto an older system. The interpreter then calls symbols whose GUD entries are not yet defined on the older NCK, which is the immediate trigger for 12550.

Root Cause Analysis

Three independent root causes converge on the same alarm text. Diagnose in this order:

1. Empty spindle lookup table. CYCLE97 builds _C97_NR[] dynamically by scanning all configured machine axes and storing $MA_SPIND_ASSIGN_TO_MACHAX[Ax] for each spindle-capable axis. If the lathe has only one main spindle but the spindle-to-axis assignment in MD 30500 / 30550 / 30350 is missing or set to 0, the loop populates only _C97_NR[0] = 0 (the initial REP(0)). Subsequent statements that address _C97_NR[1..5] (e.g. for the counterspindle or the C-axis mapping) read a zero that was never written, and the interpreter raises 12550 on the GUD symbol referenced as the assignment target.
2. GUD file not actually loaded. The DEF file is present on the CF card in user/_N_DEF_DIR/_N_GUD7_DEF but the active GUD set on the NCK is older. NCK reads the GUD set only at power-on or after an explicit PI service _N_GUD. A file-system update without an NCK reset is the most common field cause of "files are present, no data is visible in the parameter screen".
3. Protection level. GUD definitions are stored under the current access level. The operator-level (level 4) and setup-level (level 3) parameter displays do not see definitions stored at the manufacturer (level 1) or service (level 2) level unless the password for that level is set. CYCLE97 reads _C97_NR at the protection level of the calling program (typically level 0 or 1), but the values defined in the GUD are written by the cycle at the access level of the active _C97_NR[0] = REP(0) statement. Mismatched levels cause the read to return an undefined symbol.

Diagnostic Procedure

1. Confirm the alarm block. On the HMI, read the alarm screen and note the channel, block, and identifier. The third parameter of alarm 12550 is the symbol that the interpreter cannot resolve. In the source case it is _C97_NR (or _C97_NR[k] depending on the controller build). Compare the literal symbol against the symbol table.
2. List GUDs from the HMI. Navigate to Startup > GUD (or Parameters > User Data depending on HMI build). Open GUD7 (channel-specific) and check that _C97_NR, _C97_AXNAM, and _C97 are listed with the expected data type and array size. If the entries are missing entirely, the GUD file is not active.
3. Inspect the live value. From the same GUD screen, open _C97_NR[0] and read its value. A value of 0 indicates the cycle has just been initialized but has not yet populated the array. A value of 1, 4, or 5 indicates a real spindle number was assigned by $MA_SPIND_ASSIGN_TO_MACHAX.
4. Check the active file system. Use HMI Startup > File System and confirm the active partition. On a 840DE the partition is normally /card/user/.... The expected path for the GUD definition is /card/user/_N_DEF_DIR/_N_GUD7_DEF and for the cycle /card/user/_N_CST_DIR/_N_CYCLE97_SPF.
5. Read the cycle version banner. Open CYCLE97.SPF in the HMI editor. The first non-comment line should contain ;VERSION: and ;CHANGE: with a date. If the version date is newer than the loaded standard cycles (Startup > Version → Standard Cycles), you have a mixed version installation and the array layout in the DEF file may no longer match the cycle's expectations.
6. Cross-check machine data. Verify MD30350 $MA_SPIND_ASSIGN_TO_MACHAX[AX1] and MD30350 $MA_SPIND_ASSIGN_TO_MACHAX[AX2]. Both must be non-zero for a lathe that uses one main spindle and one C-axis. A value of 0 for one of them causes the FOR loop in CYCLE97 to skip the affected index, leaving _C97_NR[1] = 0 and triggering 12550 on a later reference.
7. Check option bits. Some cycles are option-gated on 840DE export systems. In Startup > Licenses > Options, confirm that the threading option (commonly listed as "Thread cutting") is enabled. A missing option shows up in alarm 12550's fourth parameter ("option %4 is not installed").

Machine Data Verification

The spindle-to-axis assignment is the most common single point of failure. The following MDs must be set in a coordinated way for CYCLE97 to populate _C97_NR correctly:

Read the live values with MD > Display MD on the HMI. For a retrofit on 840DE export, MD38010 is frequently left at the default 1 even when the mechanical scope includes a counterspindle. CYCLE97 then writes _C97_NR[1] = 0 (because no second spindle is allocated) and downstream blocks that address _C97_NR[1] raise 12550. Increasing MD38010 to 2 (or 3) and re-powering is the fix.

GUD File Verification

The GUD file GUD7.DEF declares the symbol table that the cycle writes into. The relevant block from the source case is:

;$PATH=/_N_DEF_DIR
;VERSION: 06.05.14.00 Dec 07, 2004
;CHANGE : 06.05.11.00 Oct 28, 2003
APR 11 APW 11
N10 DEF CHAN INT _ZSD[10]=0
N20 DEF CHAN REAL _C97[4]
N30 DEF CHAN INT _C97_NR[11]=SET(1,0,0,0,0,4,0,0,0,0,1)
N40 DEF CHAN STRING[8] _C97_AXNAM[5]=SET("C")
N50 DEF CHAN REAL _CONT2[10]
N51 DEF NCK INT _SC_MASK[10]=SET(0,0,0)
N300 REDEF $MC_TOOL_CARRIER_RESET_VALUE APR 7 APW 7

Three structural checks apply to this file:

1. Attribute match (APR / APW). APR 11 APW 11 sets the read and write access level to 1 (manufacturer). The cycle's write statements are at the level of the running program. If the running program has access level 4 (operator) and the GUDs are at level 1, the cycle fails to write. The standard fix on a retrofit is to change APR/APW to 7 (operator read, operator write) or to match the calling program's level. The REDEF line for the tool carrier reset must also keep the new level (here APR 7 APW 7).
2. Initial values. The SET(1,0,0,0,0,4,0,0,0,0,1) initializer primes the array with two non-zero entries (index 0 = 1, index 5 = 4) so the cycle has a valid starting point before the FOR loop overwrites the spindle entries. If this initializer is corrupted (e.g. truncated to SET(0,0,0,0,0,0,0,0,0,0,0)), the cycle cannot resolve _C97_NR[0] after the first overwrite pass.
3. Array sizes. _C97_NR[11] matches an 11-slot layout expected by the CYCLE97 implementation at 06.05.14.00. A copy of an older or newer DEF file (e.g. 10-slot or 12-slot) desynchronizes the cycle's addressing and raises 12550 on slot 10 or 11. Re-extract the file from the matching standard-cycles archive before editing.

Cycle 97 Code Analysis

The interpreter block that drives the 12550 alarm is the spindle-search loop at the head of CYCLE97:

KK=0
_C97_NR[0]=REP(0)
_C97_AXNAM[0]=REP("")
_AXZAHL=$ON_NUM_AXES_IN_SYSTEM-1
SBLOF
FOR II=0 TO _AXZAHL
  JJ=$MC_AXCONF_MACHAX_USED[II]
  IF JJ<>0
    IF $MA_SPIND_ASSIGN_TO_MACHAX[AXNAME("AX"<<JJ)]<>0
      _C97_NR[KK]=$MA_SPIND_ASSIGN_TO_MACHAX[AXNAME("AX"<<JJ)]
      _C97_NR[KK+5]=JJ
      _C97_AXNAM[KK]=$MC_AXCONF_CHANAX_NAME_TAB[II]
      KK=KK+1
    ENDIF
    IF (KK>_SPIZAHL)
      GOTOF _END_SPISUCH
    ENDIF
  ENDIF
ENDFOR
_END_SPISUCH:

Two key observations from this block:

• REP(0) and REP("") are valid initializers but the entries they write are *not* real spindle numbers. The block is intended to clear the array before the search. If the FOR loop never finds a valid $MA_SPIND_ASSIGN_TO_MACHAX value (because all the MD entries are 0), the array stays at REP(0). CYCLE97 then tries to assign _C97_NR[0] = 0 to a local variable of type INT, and the interpreter (depending on build) raises 12550 on the symbol because the runtime binding is "defined as zero, not undefined at this point".
• SBLOF suppresses single-block stop inside the loop, so the alarm is reported against the calling program block (the CYCLE95 call), not against line SBLOF. The operator sees the alarm at the CYCLE95 call site, which is why the alarm message is reported as "_C97_NR not defined" even though the cycle 95 source is correct.

Resolution Procedure

1. Back up the active GUD and the cycle file. In HMI Startup > GUD > Save to export the current GUD set. Use File System > Copy to copy CYCLE97.SPF and CYCLE95.SPF to a USB stick before any change.
2. Verify machine data for the spindle assignment. Set MD30350 $MA_SPIND_ASSIGN_TO_MACHAX for the main spindle axis to 1, and for the C-axis (or counterspindle axis, if used) to 2 or 3 as applicable. If a second spindle is mechanically present, raise MD38010 $MC_MM_NUM_SPINDLES from 1 to 2 (or 3) so the runtime can address the extra index.
3. Reload the matching DEF file. Copy the GUD7.DEF from the standard-cycles archive that matches the running cycle version (06.04.21). Do not edit the array initializers or the array sizes by hand unless the cycle is also updated. The file must reside at /card/user/_N_DEF_DIR/_N_GUD7_DEF.
4. Adjust the access levels. In the DEF file header, change APR 11 APW 11 to APR 7 APW 7 (or to the access level of the calling program). The REDEF line for the tool carrier reset must be updated to the same level. Save the file on the HMI.
5. Trigger an NCK reload. Either power-cycle the NCU (proper way) or use the HMI Startup > GUD > Activate to force a reload. The PI service _N_GUD executes the same effect without a power cycle but requires service-level access.
6. Clear the alarm and test. Press NC-Reset to clear 12550, then run a dry motion in JOG on the spindle (no thread). Run a single CYCLE95 call with a short thread (e.g. 1 mm pitch, 1 mm thread length) to confirm _C97_NR[0] and _C97_NR[1] populate correctly. Read them back from Parameters > GUD > GUD7 — the values should now show 1 and 2 (or whatever the MD assignment is), not 0.

Verification and Commissioning

After the fix, run a verification matrix to confirm the cycle behaves across the lathe's operating envelope:

Related Cycles and Common Variants

For the 802D variant of the same failure, the symbol reported in alarm 12550 is _ktl_not (or _ktl_ followed by an index). The recovery sequence is the same: verify the GUD file is active, verify the spindle MD assignment, and verify the threading option bit. The 802D controller does not use the same DEF file naming, so do not copy a 840D GUD7.DEF across to an 802D platform — the GUD layout is different.

Troubleshooting Matrix

FAQ