100104

Check PROFIBUS/PROFINET status

Navigate to Diagnostics > Hardware > PROFIBUS/PROFINET and verify all servo drives show 'RUN' status with green indicators.

Look for intermittent red flashing which indicates sporadic communication errors

Verify cable connections

Inspect PROFIBUS/PROFINET cables at NCU X101/X102 connectors and all servo drive communication ports for loose connections or damage.

Power down system before checking connections to prevent electrical damage

Check bus termination

Verify PROFIBUS terminating resistors (220Ω) are properly installed at both ends of the bus network.

Use STEP 7 hardware diagnostics to verify bus topology and termination status

Monitor cycle times

Check MD11300 $MN_SYSCLOCK_CYCLE_TIME and verify it matches the configured PROFIBUS cycle time in HW Config.

Typical values are 2ms for standard applications, 1ms for high-speed machining

Check servo drive displays

Examine all SIMODRIVE/SINAMICS drive displays for fault codes (F-codes) or warning messages (A-codes).

F01910 and F01920 are common communication-related drive faults

Review drive diagnostics

Access Diagnostics > Drives > [Axis] and check drive status, actual values, and fault buffer for each affected axis.

Clear drive faults only after identifying and correcting the root cause

Verify drive enable signals

Check that drive enable signals are active in Diagnostics > Service > Drives and verify MD30200 $MA_DRIVE_ENABLE is set correctly.

Use oscilloscope to verify enable signal integrity if intermittent issues occur

Check power supply status

Verify DC bus voltage at drives is within specification (typically 540-720VDC) and check for power supply alarms.

Low DC bus voltage can cause drives to fault intermittently under load

Monitor NCU performance

Check Diagnostics > NCU > Performance and verify CPU load is below 80% and memory usage is within normal limits.

Use MD11210 $MN_PERF_MONITOR_ENABLE=1 to activate detailed performance monitoring

Review active programs

Check for complex part programs with excessive subroutine calls or mathematical calculations that may overload the interpolator.

Look for programs with tight radius moves or high-frequency oscillations

Verify interpolation settings

Check MD20100 $MC_LOOKAH_NUM (lookahead) and MD20110 $MC_SMOOTHING_MODE settings for optimal performance.

Reduce lookahead from default 5 to 3 if experiencing performance issues

Check background tasks

Review active OEM applications, PLC programs, and HMI updates that may consume excessive NCU resources.

Disable non-essential background tasks during critical machining operations

Check system timing

Verify MD11300 $MN_SYSCLOCK_CYCLE_TIME matches hardware configuration and check for timing violations in alarm buffer.

Standard timing is 2ms for most applications, 1ms for high-speed machining

Review interrupt priorities

Check that servo control interrupts have highest priority and are not being blocked by other system tasks.

Do not modify interrupt priorities without Siemens engineering support

Verify NCU hardware

Check NCU temperature, fan operation, and memory module seating to ensure stable hardware operation.

NCU operating temperature should be below 55°C for optimal performance

Update system software

Verify NCU software version and consider updating to latest stable release if timing issues persist.

Check Siemens support portal for known timing-related software fixes