axismd.ai
Siemens SINUMERIK Controller
Servo/Axis · Intermediate · 30-120 minutes
Siemens 840D 27090 - Error in data cross check NCK-PLC, NCK:; <ALSI>
Alarm 27090 indicates a cyclic data integrity mismatch between the NCK (Numerical Control Kernel) and PLC subsystems during real-time synchronization of shared variables ($A_INSI, $A_OUTSI, $A_INSE, $A_OUTSE, or $A_MARKERSI). This cross-check failure suggests either corrupted interface data, timing synchronization loss, or a fault in the NCK-PLC communication protocol layer.
27090
Siemens 840D 27090 - Error in data cross check NCK-PLC, NCK:; <ALSI>
Error in data cross check NCK-PLC, NCK:; <ALSI>
Siemens SINUMERIK alarm 27090: Error in data cross check NCK-PLC, [], NCK:; <ALSI>. This alarm indicates a fault or error condition on the SINUMERIK 840D control. Refer to the Siemens SINUMERIK alarm documentation for the complete description and remedy.
Root Cause Summary
Alarm 27090 indicates a cyclic data integrity mismatch between the NCK (Numerical Control Kernel) and PLC subsystems during real-time synchronization of shared variables ($A_INSI, $A_OUTSI, $A_INSE, $A_OUTSE, or $A_MARKERSI). This cross-check failure suggests either corrupted interface data, timing synchronization loss, or a fault in the NCK-PLC communication protocol layer.
Safety
- Refer to Siemens documentation
- Ensure qualified technician performs repairs
Causes and Fixes
- 1
Access Diagnostics > System Information > Cycle Times and verify NCK cycle time (MD 20050) matches PLC OB35/OB40 cycle declarations. Standard is 4ms NCK with synchronized PLC update rates.
Do not modify MD 20050 during active machine operation.
- 2
Check PLC source code (SIMATIC STEP 7 environment) for $A_INSI/$A_OUTSI update blocks. Confirm these blocks execute synchronously without unconditional RETURN statements or excessive logic that might delay cycle completion.
Overloaded PLC cycles can cause watchdog timeout before cross-check completion.
- 3
Review System > Diagnostics > PLC Diagnostics for cycle time overruns (OB80 errors) or communication timeouts in the last 10-20 cycles prior to alarm occurrence.
- 4
Reset the system and enable PLC online change diagnostics (STEP 7 > Program > Diagnostics) to confirm PLC cycle jitter is <10% of NCK cycle time.
Seeing Multiple Alarms?
Seeing another alarm with this one? Enter the code.
Get machine-aware diagnosis
AxisMD logs alarms against your actual machines, tracks patterns, and gives AI context your manual doesn't have.
Start freeWas this guide helpful?
Always verify with your machine manual or a certified technician before performing service procedures.