Your tool post won’t index. The problem is not mechanical but logical: a 900-series bit parameter tells the PMC how to interface with the turret servo or hydraulic clutch. If that bit toggles due to corruption, the turret will freeze.
| Bit | Function | |------|-----------| | 7 | Axis 1 (X) servo type: 0 = analog (±10V), 1 = digital serial (FANUC α/β) | | 6 | Axis 2 (Z) servo type | | 5 | Separate detector for X axis (0 = motor encoder only, 1 = scale feedback) | | 4 | Separate detector for Z axis | | 3 | High-gain servo mode (0=off, 1=on) | | 2 | Torque limit enable | | 1-0 | Axis scaling factor (pitch error compensation) |
The 900 series is interesting because it reveals that Fanuc hardware is often the same, but the software locks differ.
You might buy a used lathe that "doesn't have rigid tapping." However, if you look at the 900-series parameters, you might find the bit for rigid tapping is simply set to 0. In the 90s, machine builders would physically sell the same machine with different features enabled/disabled via these bits.
If you are staring at a blank screen or recovering from a dead battery: fanuc ot 900 parameter list
Do you have a specific issue you are trying to solve? (e.g., enabling rigid tapping, spindle orientation, or restoring a backup?) If you share the specific parameter number you are looking at, I can tell you exactly what that bit does
This is a guide to the Fanuc Series 0-T (Model T) parameter list, specifically focusing on the critical 900-series parameters.
⚠️ CRITICAL WARNING: Incorrect settings in the 900-series parameters can render the machine inoperable, cause servo crashes, or result in dangerous rapid movements. Always back up parameters before making changes. Do not alter these unless you are a qualified service engineer or have specific instructions from the machine tool builder.
1. Never rely on screenshots alone. The Fanuc OT 900 parameter list varies by: Your tool post won’t index
2. Backup before editing.
Old Fanuc OT controls have volatile CMOS batteries. Use the PUNCH function to output all parameters to a PC:
EDIT mode → PUNCH → ALL PARAMETERS → EXEC
Save the file. Specifically, save the 900 range (N900–N999).
3. Do not "experiment" with 908 and 909.
Setting 908 incorrectly can cause a "System HALT" requiring a ROM replacement. Setting 909 without the proper option key may lock the control permanently.
4. Understand the "Parameter Number Changed" alarm.
If you change a 900 parameter and get a "P/S 000" alarm with "PLEASE TURN OFF POWER," you must cycle the control fully. Some 900 bits require a cold start. Do you have a specific issue you are trying to solve
5. Legal note:
Enabling an option via the 900 parameter list that you did not purchase may violate your license agreement with Fanuc. However, if your machine label shows "Macro B included" but it’s disabled, you have every right to re-enable it.
Note: Fanuc OT has multiple ROM versions (A, B, C, D, Mate). The exact function of each bit can vary. This list reflects the most common standard for Fanuc OT-B and OT-C.
Before viewing or modifying the list, you must enable PWE (Parameter Write Enable).
Step-by-step:
WARNING: Never change the 900 parameters arbitrarily. If you enter an invalid combination, the control may display "ROM PARITY ERROR" or fail to boot.
