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Siemens SINUMERIK Controller
Spindle · Intermediate · 30-120 minutes
Siemens 840D 21750 - Error during output of cam signals via timer
Alarm 21750 fires when the hardware timer cannot output cam signals independently of the NCK interpolation clock because the interpolation cycle (set by MD 32100 IPO_CYCLE_TIME_MS) exceeds 15 ms. The fast output mask configured in MD 10480 SW_CAM_TIMER_FASTOUT_MASK requires a sufficiently short interpolation cycle to maintain timing accuracy for spindle cam switching.
21750
Siemens 840D 21750 - Error during output of cam signals via timer
Error during output of cam signals via timer
Siemens SINUMERIK 840D alarm 21750: Error during output of cam signals via timer. 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 21750 fires when the hardware timer cannot output cam signals independently of the NCK interpolation clock because the interpolation cycle (set by MD 32100 IPO_CYCLE_TIME_MS) exceeds 15 ms. The fast output mask configured in MD 10480 SW_CAM_TIMER_FASTOUT_MASK requires a sufficiently short interpolation cycle to maintain timing accuracy for spindle cam switching.
Safety
- Refer to Siemens documentation
- Ensure qualified technician performs repairs
Causes and Fixes
- 1
Access Siemens HMI > Diagnostics > Parameters > Machine Data. Navigate to MD 32100 IPO_CYCLE_TIME_MS and verify current value.
Do not modify IPO_CYCLE_TIME_MS without consulting machine tool builder specifications; this affects all interpolation timing.
- 2
If IPO_CYCLE_TIME_MS > 15 ms, reduce to ≤15 ms (e.g., 12 ms or 10 ms). Use increments of 1-2 ms to avoid destabilizing servo loop response.
- 3
Verify MD 10480 SW_CAM_TIMER_FASTOUT_MASK bit assignment is correct for spindle cam output channels (typically bits 0-3 for spindle A-D).
- 4
Perform cold restart (POWER ON/OFF cycle) of the control. Test spindle cam switching function via manual spindle orientation or synchronized spindle program block.
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Always verify with your machine manual or a certified technician before performing service procedures.