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Siemens SINUMERIK Controller
Spindle · Intermediate · 30-120 minutes
Siemens 840D 16794 - Channel block coupling of axis/spindle prohibits reference
Alarm 16794 fires when a reference point approach (G74/G75) is commanded on a slave axis within a gantry or coupling configuration. The NCK detects that the axis is coupled via MD32100 (Axis coupling type) and blocks the reference move because slave axes must synchronize through their master axis, not independently.
16794
Siemens 840D 16794 - Channel block coupling of axis/spindle prohibits reference
Channel block coupling of axis/spindle prohibits reference
Siemens SINUMERIK 840D alarm 16794: Channel block coupling of axis/spindle prohibits reference. This alarm indicates a program or channel-level error on the SINUMERIK control. The part program or machine function cannot be executed as commanded.
Root Cause Summary
Alarm 16794 fires when a reference point approach (G74/G75) is commanded on a slave axis within a gantry or coupling configuration. The NCK detects that the axis is coupled via MD32100 (Axis coupling type) and blocks the reference move because slave axes must synchronize through their master axis, not independently.
Safety
- Refer to Siemens documentation
- Ensure qualified technician performs repairs
Causes and Fixes
- 1
Navigate to Diagnosis > Parameters > Machine data > Axis-specific (MD) and locate the affected axis. Check MD32100 (Coupling type) value. If value = 1 (gantry slave), 2 (spindle slave), or similar coupling mode, the axis is coupled.
Do not modify MD32100 during machine operation.
- 2
Verify MD32110 (Coupling master axis) points to the correct master axis name. Confirm via Diagnosis > Axis overview that master and slave axes are correctly paired.
- 3
Issue reference point command (G74/G75) on the master axis listed in MD32110, not on the slave axis. The slave will auto-synchronize during master reference via MD32120 (Coupling response) settings.
Ensure master axis reference is complete before resuming coupled motion.
- 4
After master reference completes, verify both axes are referenced via Diagnosis > Actual values. Check axis status display shows 'REF' (referenced) for both master and slave.
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