axismd.ai
Heidenhain Controller
Communication · Intermediate · 30-120 minutes
HEIDENHAIN 126-0112 - Switch-off port on incorrect bus system
This alarm is triggered by a configuration error where safety-critical switch-off outputs are assigned to or detected on an inappropriate bus system within the Heidenhain control architecture. The control's safety monitoring detects this topology violation because switch-off ports must operate on designated safety-rated bus segments (typically the main PLC bus) rather than on encoder or non-safety peripheral buses to maintain functional safety integrity per the control's safety certification requirements.
126-0112
HEIDENHAIN 126-0112 - Switch-off port on incorrect bus system
Switch-off port on incorrect bus system
The shutdown output was mapped to a bus system that is not allowed for this purpose. Valid choices are external PL units with HSCI link or internal PL assemblies.
Root Cause Summary
This alarm is triggered by a configuration error where safety-critical switch-off outputs are assigned to or detected on an inappropriate bus system within the Heidenhain control architecture. The control's safety monitoring detects this topology violation because switch-off ports must operate on designated safety-rated bus segments (typically the main PLC bus) rather than on encoder or non-safety peripheral buses to maintain functional safety integrity per the control's safety certification requirements.
Safety
- Refer to Heidenhain service manual
- Ensure qualified technician performs repairs
Causes and Fixes
- 1
Access MOD configuration
Navigate to SYSTEM (MOD key) → Machine Parameters → MOD Settings. Locate the switch-off port configuration section, typically under 'CfgSafetyRelay' or similar safety output parameters.
Make a backup copy of your current MOD file to CF card before making changes - use MOD function → Backup Machine Parameters.
- 2
Identify bus assignment
Review the bus node assignment for each switch-off port entry. Look for parameters like 'BusType' or 'NodeAddress' - these should reference PLC bus nodes (typically MC or CC PLC channels), not EIB nodes.
Do not change safety-related parameters without proper authorization and machine manufacturer documentation.
- 3
Correct bus assignment
Modify the switch-off port configuration to assign it to the correct PLC bus node. Change bus type from 'EIB' to 'PLC' or update the node address to match the physical safety I/O module location (e.g., CC6xx PLC node instead of EIB encoder node).
- 4
Reboot and verify
Perform a complete control restart (power cycle recommended). After reboot, check SYSTEM → Diagnose → PLC → I/O Status to confirm the switch-off port now appears on the correct bus system and alarm clears.
Use Service → System Info → Component Tree to visually verify which bus each component is assigned to after the change.
Call a technician if:
- ·If IO configuration corrections do not resolve the issue after multiple attempts
- ·If hardware failure is suspected and replacement parts are not readily available or expertise is lacking
Prevention
- Regularly review and document IO configurations to prevent misassignments during updates or maintenance.
- Perform routine firmware and software updates to maintain compatibility with bus systems.
- Schedule periodic hardware inspections to identify and address potential failures before they cause alarms.
Common Mistakes
- Failing to document original IO configurations before making changes, leading to difficulty in rollback.
- Using incompatible or unverified hardware components for bus system connections, risking further errors.
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.