Introduction: The "Secret" Parameters of the Fanuc OT Control
The Fanuc OT (also written as Fanuc 0T) is one of the most iconic and widely used CNC controls for lathes and turning centers. Despite being introduced in the mid-1980s, thousands of machines worldwide still rely on this resilient, workhorse control.
While most operators are familiar with standard parameters (0000–8999), there exists a mysterious and often misunderstood range: Parameters 900 to 999.
Colloquially known as the "900 Parameters," or the "Option Parameters," this list holds the keys to your machine’s capabilities. Unlike standard settings that control axis tuning or I/O configuration, the 900 parameters enable or disable purchased options—features like rigid tapping, macro programming, AI contour control, and additional axes.
This article provides an exhaustive breakdown of the Fanuc OT 900 parameter list, explaining what each bit does, how to access them, and critical precautions to take before making any changes.
If you have a Fanuc 0T-D or 0T-TT (Twin Turret), the parameter list for the 900 range can differ significantly.
| Bit | Function | |------|-----------| | 7 | DNC drip-feed baud rate override | | 6 | Remote buffer (32K) enable – required for complex programs | | 5 | High-speed serial (RS-422/RS-232C) | | 4 | Tape mode without parity check | | 3-0 | Communication protocol version |
Most operators know parameters 000–899: axis gains, acceleration times, RS232 settings. But parameters 900 through 939 are different. They are option parameters – they tell the CNC what hardware and software features are installed.
Without them, the control doesn’t know: fanuc ot 900 parameter list
Diego’s machine was dead because the control had reverted to factory defaults: no options enabled, wrong PMC type, no axis configuration.
This helps the control identify the generation of the servo system.
The 900 parameters are not in the standard Fanuc manual – they are machine-builder specific. Never trust a generic list from the internet (unless you’re desperate).
Always back up your 900 parameters (and all others) via RS232 to a PC, and print the 900 list on paper. Old Fanuc OT controls can’t be backed up with a USB stick.
If you lose the 900 list, call the machine tool builder – not Fanuc. Fanuc only knows the hardware options they sold to the builder, not how the builder configured the PMC or axis assignments.
Some 900 parameters control serious things:
Write them down today. If your Fanuc OT battery dies and the 900 list is lost, even a Fanuc field tech will have to reverse-engineer the machine’s behavior.
Want to check yours? On a Fanuc OT, press DGNOS/PARAM → soft key right to PARAM → type 900 → INPUT. If you see zeros for everything, someone never set them – or you’ve just had a memory loss. Unlocking the Core: The Complete Guide to the
Demystifying the Fanuc 0-T 900 Series Option Parameters The Fanuc 0-T controller is a legendary workhorse in the CNC world, especially for lathes. If you’ve ever tried to customize your machine or restore it after a battery failure, you’ve likely bumped into the mysterious 900 series parameters. Unlike standard parameters, these "option bits" are the digital switches that unlock specific software features your machine may or may not have been purchased with. What are the 900 Series Parameters?
On a Fanuc 0-T, parameters 900 through 999 are typically Option Parameters. Each parameter number consists of 8 bits (labeled 7 down to 0), and each bit acts as a toggle (0 for OFF, 1 for ON) for a specific feature like canned cycles, extra memory, or conversational programming. Key 900 Parameter Breakdown
While every machine is unique based on its original manufacturer (OEM) specs, here are some of the most common 900 series bits found on the 0-T system: Parameter 900: General Programming Options Bit 0: Canned Cycles (G70-G76) Bit 1: G10 Program Input of Offsets Bit 3: Manual Pulse Generator (Handwheel) control Bit 5: Inch/Metric Conversion Parameter 901: Memory and Interface
Bits 0-4: Tape Memory Additions (Increasing storage from 20M up to 320M) Bit 5: Chamfering and Corner Radius features Bit 7: Multiple Repetitive Canned Cycles Parameter 902: Advanced Control Bit 2: Constant Surface Speed Control (CSS) Bit 6: Custom Macro A Parameter 903: Display and Interface Bit 5: Increases number of storable programs to 125 Bit 7: Enables soft keys below the CRT screen How to Access and Edit Them
Editing these requires caution, as an incorrect bit can cause system alarms or disable critical machine functions.
Enter MDI Mode: You cannot change parameters while in Auto or Jog. Enable PWE (Parameter Write Enable): Press the SETTING key. Locate "PARAMETER WRITE" and change the 0 to a 1.
The machine will likely throw a P/S 100 Alarm (Parameter Write Enabled). This is normal; just leave it until you’re done.
Find the 900s: Press the PARAM key and page down or search for 900. ⚠️ A Critical Safety Note If you have
Edit with Care: Use the cursor to highlight the bit you need to change, type the new 8-bit string (e.g., 00010001), and press INPUT.
Reboot: Many 900-series changes require a full power cycle to take effect. A Vital Warning Fanuc Ot 900 Parameter List - Google Groups
The Fanuc 0T Series (including 0T-A, 0T-B, and 0T-C) uses the 900 series parameters to enable specific software options and machine features. These are binary bit-level parameters where each number (900, 901, etc.) contains 8 individual bits (numbered 0 to 7) that function as on/off switches for features like canned cycles, additional memory, and macro programming. Critical Preparation & Safety
Warning: Changing 900-series parameters can disable your machine or cause severe damage if done incorrectly.
Backup Everything: Always perform a full SRAM backup or manually record every existing parameter before making changes.
PWE (Parameter Write Enable): You must enable PWE to make changes. Switch to MDI Mode. Press the SETTING function key.
Find PARAMETER WRITE and change it from 0 to 1. An "ALM 100" (PWE enabled) will appear; this is normal. Fanuc 0T 900-Series Parameter List
Below are the most common bit settings found in 900-series parameters for the 0T control. | Parameter | Bit | Description |
| :--- | :--- | :--- || 900 | 0 | Canned Cycle (G70-G76) || | 1 | G10 Program Input of Offset || | 3 | Manual Pulse Generator (Handle) || | 5 | Inch / Metric Conversion || 901 | 1 | Tape Memory Addition (120M) || | 5 | Chamfering and Corner Radius || | 7 | Multiple Repetitive Canned Cycles || 902 | 2 | Constant Surface Speed (G96/G97) || | 6 | Custom Macro A || 903 | 1 | X-Axis Mirror Image || | 7 | Soft Keys (Below CRT) || 910 | 1 | Work Offsets (G54–G59) || 911 | 2 | Rigid Tapping || 912 | 0 | 3rd / 4th Reference Point Return | How to Edit 900-Series Parameters Fanuc 900 Parameter List Overview | PDF - Scribd
If your battery died and you have no backup, attempt this recovery sequence:
10001000 (X & Z only), param 901 = 00000000 (spindle no special options), param 902 = 01000000 (PMC-R default).- and . while powering up → enter boot menu → load from PCMCIA if a backup exists.