239-01B3

Check current encoder cycle time

Navigate to MOD > Machine Parameters > MP7440 ENDAT_CYCLE_TIME and note the current value. Values below 125μs often cause this alarm with multiple encoders.

Document all encoder types and resolutions before making changes

Increase cycle time incrementally

Increase MP7440 from current value by 25μs increments (e.g., from 100μs to 125μs). Restart control after each change.

Do not exceed 500μs as this may affect positioning accuracy

Test axis movement

Perform reference run on all axes and execute test program with rapid movements to verify alarm clearance and maintained performance.

Monitor FS communication load

Check diagnostic screen PLC > Info > FS Communication to verify telegram load is below 80% after changes.

Review encoder resolution settings

Check MP4210-MP4270 (encoder input assignment) and MP4110-MP4170 (lines per revolution) for all axes. Note any encoders >1,000,000 counts/rev.

Linear encoders with 0.1μm resolution are common culprits

Reduce encoder resolution if possible

For non-critical axes, reduce MP41xx values to lower resolution (e.g., from 5,000,000 to 1,000,000 lines/rev) while maintaining required accuracy.

Coordinate with machine manufacturer before changing encoder parameters

Adjust EnDat telegram content

Access Setup > EnDat Configuration and disable unnecessary additional information telegrams (temperature, diagnostics) to reduce communication load.

Verify system performance

Run precision test programs to ensure reduced resolution still meets machining requirements.

Inventory FS bus devices

Navigate to PLC > Info > FS Devices and document all connected devices including encoders, safety I/O, and communication modules.

Each EnDat encoder counts as 2-3 device units depending on configuration

Check FS bus load parameters

Review MP7441 (FS bus cycle time) and MP7442 (max FS devices). Compare actual device count against maximum allowed.

Never exceed manufacturer's maximum device count specifications

Redistribute devices if possible

Move non-critical devices to standard I/O bus or implement secondary FS communication module if available on your TNC model.

Optimize device priorities

Use Setup > FS Configuration to set lower priority for non-safety critical devices, allowing safety encoders priority access.

Check encoder error counters

Navigate to Diagnostics > Encoder Status and review error counters for all EnDat encoders. Look for CRC errors, timeout errors, or excessive retransmissions.

Error rates above 1 per 10,000 cycles indicate encoder problems

Isolate suspect encoder

Temporarily disconnect encoders one at a time and restart control to identify which encoder triggers the alarm.

Disable affected axes in MP200x before disconnecting encoders

Verify encoder cable integrity

Check EnDat cable for damage, proper shielding connection, and correct impedance. Measure cable resistance and continuity.

EnDat cables are sensitive to electromagnetic interference from servo drives

Test encoder communication quality

Use TNC encoder test function in Setup > Encoder Test to verify signal quality and timing parameters for the suspect encoder.

Verify FS firmware versions

Check MOD > Version Info > FS Microcontroller and compare with TNC software version. Ensure compatibility per Heidenhain documentation.

FS firmware should typically match TNC software major version

Check communication protocol settings

Verify MP7443 (FS protocol version) matches the installed FS microcontroller capabilities. Reset to default if uncertain.

Incorrect protocol settings can cause system instability

Update FS microcontroller firmware

If version mismatch found, update FS firmware using TNC Update function with proper Heidenhain firmware file.

Never interrupt firmware update process - ensure stable power supply

Restore optimized parameters

After firmware update, restore machine parameters from backup and re-optimize FS communication settings.