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FANUC Controller
Servo/Axis · Intermediate · 5-30 minutes
Fanuc 494 - Fssb slave count error
FSSB alarm 494 indicates a mismatch between the number of servo amplifiers the CNC expects to find on the serial servo bus and the number actually detected during initialization or runtime. This typically occurs during power-up when the control counts connected slaves, or when a communication dropout causes a slave to disappear from the bus.
494
Fanuc 494 - Fssb slave count error
FSSB SLAVE COUNT ERROR
An FSSB (Fanuc Serial Servo Bus) error has been detected related to fssb slave count error. The serial bus communication between the CNC and servo amplifiers is affected.
Root Cause Summary
FSSB alarm 494 indicates a mismatch between the number of servo amplifiers the CNC expects to find on the serial servo bus and the number actually detected during initialization or runtime. This typically occurs during power-up when the control counts connected slaves, or when a communication dropout causes a slave to disappear from the bus.
Safety
- Verify corrected program or parameters before resuming machining
Causes and Fixes
- 1
Check parameter 8000 (or 8100 depending on Fanuc series) for the configured number of FSSB slaves.
- 2
Physically count the number of servo amplifiers connected to the FSSB fiber optic or cable loop and verify each has power LED illuminated.
- 3
Compare the physical count with the parameter value. If mismatched, correct parameter 8000 to reflect actual connected amplifiers.
Changing FSSB configuration parameters requires a full power cycle to take effect. Ensure proper backup before modification.
- 4
Power cycle the entire system (CNC and amplifiers) and verify alarm clears during boot sequence.
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