CYCLE800 Swivel Detection and Reset on 840D sl at Program Startup

Overview: CYCLE800 Swivel Persistence Across NC Reset

CYCLE800 is the Siemens swivel cycle for 5-axis and turn-mill machines. On a SINUMERIK 840D sl it computes and applies a frame rotation that aligns the tool plane to a tilted surface or to a swiveling milling head, writes the result into a settable frame (G54–G599), and selects the matching active plane (G17 / G18 / G19). The cycle is documented in the SINUMERIK 840D sl Programming Manual Cycles (PGZ) and is shipped as a Siemens standard cycle that machine builders (including DMG MORI on the CTX Gamma 2000 TC) overwrite or extend with their own compile cycle.

By design, most machine builders configure the NCK to retain the active swivel after NC reset and after M30. The intent is production-friendly: an operator who is re-running the same program does not have to re-enter the swivel data record before each run. The active data record remains visible on the work-offset page together with the active plane and the rotation angle, and the operator can re-select it from the HMI at any time. The retention behavior is documented in the PGZ manual under the "CYCLE800 startup" section, which states that the existing swivel data record is kept and can be re-selected (toggled).

The side effect is the symptom most teams hit in production: a new program calls CYCLE800 with a different data record, the controller sees an active swivel and refuses to overwrite it cleanly, and the operator is left with a "swivel data record already active" alarm and a work-offset page that still shows the previous plane. This reference covers the engineer-facing answer: detect the active swivel at NC startup by inspecting frame system variables, then clear the residual programmatically before the next CYCLE800 runs.

Three mechanisms are described, in order of safety:

1. Detect the active swivel in NC code by reading $P_UIFR and $P_CHBFR rotation components.
2. Programmatically clear the swivel by direct frame write, by ROT/AROT plus G500, or by a follow-up CYCLE800 deselect call.
3. Wire the detect-plus-clear sequence into PROG_EVENT.SPF so it fires automatically at every NC start.

CYCLE800 Cycle Mechanics on 840D sl

CYCLE800 is a compile cycle that lives in one of three NCK cycle directories. The search order at cycle call is fixed and is the same one the Siemens documentation uses for CYCLE800, CYCLE81, CYCLE832 and the rest of the cycle library.

The call form for the standard Siemens cycle is documented in the PGZ manual and is typically invoked as:

with the parameter meanings summarized below. The exact parameter set depends on the release of the cycle shipped with the firmware; always confirm against the active cycle on the machine by opening the cycle in the editor and matching the DEF line.

When the cycle finishes, the work-offset frame referenced by _FR contains the translation and rotation of the swiveled coordinate system, the plane is set to G17, G18, or G19 according to the new tool axis, and the active data record is remembered in the NCK. The operator can re-select it from the HMI work-offset page. The PGZ manual calls out this retention explicitly: the existing swivel data record is kept and can be toggled from the operator screen.

On reset, the NCK does not zero that frame. Reset and M30 are treated by the OEM as "I want to re-run the same setup", and the data is preserved. The PGZ manual documents the data-record behavior in the CYCLE800 startup section; the retention is configured by the machine builder at commissioning, not by an operator-accessible switch.

Frame System Variables for Swivel Detection

The 840D sl frame chain is documented in the Siemens Industry Online Support portal under the SINUMERIK 840D sl Programming Manual Basics (PGA) and in the SINUMERIK 840D sl Lists (Book 2) reference. The variables that matter for detecting an active CYCLE800 are:

For a CTX Gamma 2000 TC the OEM cycle typically writes the rotation into the UIFR referenced by _FR, but it may also chain a small rotation into $P_CHBFR[$P_IFRAME] when the machine builder wants the operator's G54–G59 view to stay clean. Always inspect both.

Frame components are accessed with two indices: AX selects the axis and MI selects the component kind. The full table from the PGA / PGZ manuals is repeated here because off-by-one errors on MI are a common source of false negatives.

To check whether the active UIFR carries a swivel rotation, the relevant components are MI=4 on the three axes. The CTX Gamma 2000 TC B-axis swivel typically produces a non-zero value in $P_UIFR[$P_IFRAME, 1, 4] (X rotation in degrees) or, on machines with a table-mounted C-axis, in $P_UIFR[$P_IFRAME, 3, 4] (Z rotation).

Detecting an Active Swivel from NC Code

Use a small block of NC code at the top of the program (or in PROG_EVENT.SPF) to inspect the active frame and decide whether to clear. The example below reads the three rotation components of the active UIFR and of the active chain basic frame, then flags a swivel as active if any rotation magnitude exceeds a small tolerance.

; NC program - detect CYCLE800 swivel at startup
DEF REAL _RX_UIFR, _RY_UIFR, _RZ_UIFR
DEF REAL _RX_CHB, _RY_CHB, _RZ_CHB
DEF REAL _TOL = 0.0005

; Read rotations in degrees from active settable frame
_RX_UIFR = $P_UIFR[$P_IFRAME, 1, 4]
_RY_UIFR = $P_UIFR[$P_IFRAME, 2, 4]
_RZ_UIFR = $P_UIFR[$P_IFRAME, 3, 4]

; Read rotations in degrees from active chain basic frame
_RX_CHB = $P_CHBFR[$P_IFRAME, 1, 4]
_RY_CHB = $P_CHBFR[$P_IFRAME, 2, 4]
_RZ_CHB = $P_CHBFR[$P_IFRAME, 3, 4]

IF ABS(_RX_UIFR) > _TOL OR ABS(_RY_UIFR) > _TOL OR ABS(_RZ_UIFR) > _TOL \
   OR ABS(_RX_CHB) > _TOL OR ABS(_RY_CHB) > _TOL OR ABS(_RZ_CHB) > _TOL
  ; Active CYCLE800 swivel detected in work-offset chain
  MSG("Residual CYCLE800 swivel in frame " << $P_IFRAME << " - clearing")
  ; (clear block goes here, see next section)
ENDIF

The tolerance (_TOL = 0.0005 deg) is intentional. A clean G54–G59 frame has a true zero for the rotation components, but floating-point read-back can return sub-nanometer residue from previous AROT/ROT operations. 0.0005 deg is well below the smallest swivel increment the operator can enter on a CTX Gamma 2000 TC (the HMI shows angles in 0.001 deg steps) and will not trigger on floating-point noise.

Two refinements worth adding in production code:

1. Read $P_UIFRNUM first to learn the upper bound of n, then loop over all settable frames, not just the active one. A previous program may have left a swivel in a non-active frame that becomes active on the next G55 / G56 select.
2. Use IF $AC_PLANE <> 17 GOTOF _NO_SWIVEL as a fast pre-check. CYCLE800 almost always leaves the plane different from G17 on a 5-axis machine; if you are still on G17 and the rotation values are zero, you can skip the more expensive checks. Do not rely on plane alone, because some B-axis swivels keep G17 active for a 90 deg B rotation around X.

Programmatic Reset of CYCLE800 Data

Three methods are usable in an NC program. Pick the one that matches what your OEM allows and what the channel MDs permit for direct frame writes.

Method A: Direct write to $P_UIFR and $P_CHBFR

The most surgical method. Issue ROT to clear the active programmable frame, then zero the rotation components of the active settable frame and the active chain basic frame. This is the recommended approach when the operator's G54–G59 base offsets must not be touched.

; Clear CYCLE800 swivel residue
ROT
AROT X0 Y0 Z0
IF $P_IFRAME > 0
  $P_UIFR[$P_IFRAME, 1, 4] = 0
  $P_UIFR[$P_IFRAME, 2, 4] = 0
  $P_UIFR[$P_IFRAME, 3, 4] = 0
  $P_CHBFR[$P_IFRAME, 1, 4] = 0
  $P_CHBFR[$P_IFRAME, 2, 4] = 0
  $P_CHBFR[$P_IFRAME, 3, 4] = 0
ENDIF

Method B: SETFR / G500 plus Programmable Frame Clear

SETFR(n, m) selects settable frame m in the G-group of frames 1–30. The cleanest way to drop a residual swivel without touching the operator's base offsets is to deselect the settable frame entirely with G500 and clear the programmable overlay with ROT.

; Anchor on a known-clean deselected state
G500
ROT
AROT X0 Y0 Z0

With G500 active, $P_IFRAME reads 0 and the settable frame component is bypassed, so any residual rotation in G54 no longer affects the kinematics. The next CYCLE800 call writes into the frame it is configured for (via the _FR parameter) and the residual is overwritten. Method B is the safest when the channel MDs block direct frame writes.

Method C: Re-Call CYCLE800 with a Deselect Strategy

Per the PGZ manual, you can deselect the active swivel by calling CYCLE800 with a data record configured for deselect, or by calling the cycle with a parameter combination that puts the machine back to a known un-swiveled state. On a CTX Gamma 2000 TC the typical DMG MORI approach is to use the cycle's retract or unload sequence, which is usually wrapped behind a machine-specific M function (often in the M40–M45 series for head change).

; Example - confirm against your machine's OEM documentation
CYCLE800(0, 0, 0, 0, "DESELECT", 0)
; Or, on DMG MORI:
M75   ; DMG MORI swivel retract (example only)

The exact parameter set is OEM-specific and is best confirmed in the machine's documentation, because the DMG MORI cycle typically wraps a proprietary M function around the CYCLE800 call. The Siemens-side general call form is in the PGZ manual; the wrapper M functions and the data-record names are DMG MORI territory and live in the machine's service documentation.

Startup Program Integration with PROG_EVENT.SPF

The 840D sl supports a program event cycle that fires at program start, end, and (depending on firmware) reset. The mechanism is documented in the Programming Manual Basics (PGA). You create a cycle named PROG_EVENT.SPF in the right cycle directory and the controller calls it automatically with an event ID that distinguishes the trigger.

Cycle body for a CTX Gamma 2000 TC that needs to clear residual swivel at every NC start:

PROC PROG_EVENT(INT _EV_ID)
DEF INT _EV_ID
DEF REAL _RX, _RY, _RZ, _TOL = 0.0005

IF _EV_ID == 1
  ; ---- Program start: clear residual CYCLE800 swivel ----
  IF $P_IFRAME > 0
    _RX = $P_UIFR[$P_IFRAME, 1, 4]
    _RY = $P_UIFR[$P_IFRAME, 2, 4]
    _RZ = $P_UIFR[$P_IFRAME, 3, 4]
    IF ABS(_RX) > _TOL OR ABS(_RY) > _TOL OR ABS(_RZ) > _TOL
      ; Reset settable frame rotation
      $P_UIFR[$P_IFRAME, 1, 4] = 0
      $P_UIFR[$P_IFRAME, 2, 4] = 0
      $P_UIFR[$P_IFRAME, 3, 4] = 0
    ENDIF
    ; Reset chain basic frame rotation
    $P_CHBFR[$P_IFRAME, 1, 4] = 0
    $P_CHBFR[$P_IFRAME, 2, 4] = 0
    $P_CHBFR[$P_IFRAME, 3, 4] = 0
  ENDIF
  ; Drop any programmable overlay and deselect the active frame
  ROT
  AROT X0 Y0 Z0
  G500
  MSG("PROG_EVENT: residual CYCLE800 swivel cleared")
ENDIF

IF _EV_ID == 2
  ; ---- Program end: park the swivel head (DMG MORI OEM call) ----
  ; Insert your machine's swivel retract sequence here if needed
ENDIF

M17

Notes on the cycle:

• The cycle must end with M17, not M30. M30 is a program-end marker and would create a recursive call into the same event.
• The cycle must be stored in /coi/cus/cycles/ (or in /coi/coa/cycles/ if shop policy places it there). The 840D sl searches for PROG_EVENT.SPF in the configured cycle directories at NCK start.
• Calling SETFR is not strictly necessary if the goal is "any subsequent CYCLE800 starts clean". The next CYCLE800 call overwrites the active frame's rotation by definition.
• The MSG line appears in the operator message bar of SINUMERIK Operate and is invaluable when debugging the first install. Remove it for production if the message line is needed for other alarms.

DMG MORI CTX Gamma 2000 TC Specifics

The CTX Gamma 2000 TC is a turn-mill machine with a milling head on a B-axis (swivel rotary axis) and a C-axis on the main spindle. The control is a SINUMERIK 840D sl with PCU 50 or PCU 50.5 running SINUMERIK Operate. The B-axis and C-axis are configured as the swivel axes for CYCLE800, and the machine builder's cycle wraps additional M functions around the basic CYCLE800 call for head change and retraction.

DMG MORI's CYCLE800 differs from the Siemens standard in three ways that matter for the reset problem:

1. OEM compile cycle. DMG MORI ships its own CYCLE800 in the OEM directory with extended screen masks and a wider set of data records. The parameter names and data-record strings that the Siemens PGZ manual documents may not match the names on your HMI. The general call signature CYCLE800(_FR, _TC, _ST, _MODE, _NAME, _DMODE) is preserved, but the string literals are OEM-specific.
2. Machine-specific M functions. DMG MORI wraps head-retract and tool-change operations behind proprietary M codes in the M40–M45 range (and similar). The clear-then-recall approach from Method A is a common pre-condition for these M codes; if the active swivel is not cleared, the next M call for head retract can refuse to execute with an OEM alarm that points back to CYCLE800.
3. Frame-write protection. The default commissioning of a CTX Gamma 2000 TC marks G54 as the machining frame and G55–G59 as the work offsets. Some sites also configure a swivel base frame in $P_NCBFR[1]. Direct writes to protected frames can be rejected, so Method A and Method B need to be tuned per the active configuration.

For the OEM-specific bit, the authoritative source is the DMG MORI service documentation set that ships with the machine. The Siemens-side general behavior is in the PGZ manual. The two are compatible at the system-variable level, but the data-record names and the additional frame slots live on the DMG MORI side of the boundary.

Frame Component Index Reference

The double-index access $P_UIFR[n, AX, MI] is a frequent source of off-by-one errors. The full table (consolidated from the PGA and PGZ manuals):

Same [AX, MI] structure applies to $P_CHBFR[n, AX, MI], $P_NCBFR[n, AX, MI], $P_WPFR[n, AX, MI], and $P_CYCFR[AX, MI]. $P_PFRAME, $P_OTFRAME, and $P_SETFRAME are accessed with the same AX, MI scheme but without an n index.

Verification and Commissioning Steps

Use this sequence on a CTX Gamma 2000 TC (or equivalent 840D sl turn-mill) to confirm the reset logic works end to end.

1. Power on the machine. Wait for NCK ready and SINUMERIK Operate to load.
2. Switch to the work-offset page. Note that G54 is the default and rotation reads 0.000 deg.
3. Select a swivel data record from the OEM HMI, e.g. B_AXIS_TC. Confirm the work offset page now shows G54 rotation = 90.000 deg (or whatever the data record specifies).
4. Run a test program that contains CYCLE800(1, 1, 0, 0, "B_AXIS_TC", 0). The head swivels, the plane changes, and the work offset shows the rotation.
5. Press NC reset. The program is deselected, the head does not move, and the work offset page still shows the rotation. This is the OEM retention behavior and is expected.
6. Run the new PROG_EVENT.SPF by pressing NC start on a small wrapper program. Verify that the work offset page now shows rotation = 0.000 deg after the startup event fires, and that the message line shows the "PROG_EVENT: residual CYCLE800 swivel cleared" string.
7. Run a fresh CYCLE800(1, 1, 0, 0, "C_AXIS_TABLE", 0) with a different data record. The cycle should accept the call without raising the "swivel already active" alarm.
8. Cycle power on the machine. Verify PROG_EVENT.SPF fires on the next NC start and clears the residual as expected.
9. Run the operator's normal daily program set for one shift. Watch the alarm log for any "swivel" or CYCLE800-related entries.
10. Back up the modified PROG_EVENT.SPF, the directory listing of the cycle directory, and the current $P_UIFR / $P_CHBFR snapshot from the HMI diagnostics screen. These three artifacts are the rollback package.

If step 6 fails (rotation still shown), check in order: (a) the cycle is in the right directory and named exactly PROG_EVENT.SPF; (b) the event ID is what the firmware expects (some 840D sl builds use event 1 for "start" and event 3 for "reset"); (c) the active settable frame at the time PROG_EVENT runs is the same frame CYCLE800 writes to (G54 in the default config); (d) channel MDs are not blocking direct frame writes.

Troubleshooting Matrix

Lifecycle State Diagram

Field-Proven Cautions

• Tolerance is essential. 0.0005 deg below the HMI resolution avoids false positives from floating-point residue in the frame read-back. Going below 0.0001 deg trips the check on perfectly clean frames because the read-back of 0.0 in floating point is rarely exact.
• Always inspect both UIFR and CHBFR. Some shops configure CYCLE800 to write to the chain frame in order to keep G54 clean for the operator. Reading only $P_UIFR leaves the chain frame as a hidden trap, and the next CYCLE800 will still report a conflict.
• PROG_EVENT.SPF must not contain M30. An M30 at the end of PROG_EVENT will recurse into a fresh program-end event and can stall the NCK on some firmware versions. Use M17 to return from the event cycle.
• Do not blanket-reset on every event when the shop relies on persistence. Some production programs intentionally start with a swivel that the operator set up on the previous shift. Clearing it loses that setup. If the shop relies on the operator's setup persistence, put the clear logic in a dedicated reset program the operator runs only between part families, not in PROG_EVENT.SPF.
• $P_IFRAME can be 0 (G500). Writing $P_UIFR[0, ax, mi] = 0 is harmless but does nothing useful; the G500 frame slot is a no-op. Guard the write with IF $P_IFRAME > 0 if the active frame can be 0 at startup.
• PLC-side reset signals. The PLC can also clear swivel data via DB accesses to the NCK (for example through the NC-Variable interface / NCVAR selector). That is a different path; this article covers the NC-side path only. Use the PLC path only when you need to clear from a non-NC state, such as a mode change or a controlled emergency stop.
• Alarm text is the faster first check. The Siemens-side alarm number for a CYCLE800 conflict is 61284 in many configurations; DMG MORI raises its own OEM alarms with their own numbering. Read the alarm text on the HMI first; the text usually points at the CYCLE800 line in the program and at the data record that is already active, which tells you whether the residual lives in $P_UIFR or in $P_CHBFR.
• Back up before you ship the cycle. Snapshot /coi/cus/cycles/PROG_EVENT.SPF (or wherever you store it) to the engineering server and to the machine's archive directory. If a future commissioning change regenerates the cycle directory, the PROG_EVENT.SPF is the first thing to be lost and the last thing the maintenance team will remember.

FAQ