What causes FANUC alarm 101?

RS-232 cable disconnected or loose at CNC or external device end. Communication parameters (baud rate, stop bits, parity) mismatch between CNC and device. External DNC software not running or serial port not active. Cable length too long for the selected baud rate — RS-232 limit is ~15 meters. Electrical noise on the RS-232 cable causing data corruption.

How do I fix FANUC alarm 101?

1. Verify the external device is connected and the DNC software is running. 2. Check the RS-232 cable at both ends — confirm it is fully seated. 3. Verify communication parameters match exactly on both the CNC and the external device. 4. Try reducing the baud rate to improve reliability over longer cable runs. 5. Check cable routing away from high-current lines that may cause EMI interference.

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FANUC Controller

Communication · Intermediate · 15-30 minutes

Alarm 101

Fanuc Alarm 101 - Communication Framing

Fanuc Alarm 101 indicates a framing error during serial communication between the CNC and external devices (PC, DNC, peripheral equipment). This occurs when the receiving device detects incorrect start/stop bits, incorrect data format, or mismatched communication parameters such as baud rate, parity, stop bits, or data bits between the CNC and connected equipment.

FANUCCommunicationIntermediate15-30 minutes

101

Fanuc Alarm 101 - Communication Framing

Framing Error

Root Cause Summary

Fanuc Alarm 101 indicates a framing error during serial communication between the CNC and external devices (PC, DNC, peripheral equipment). This occurs when the receiving device detects incorrect start/stop bits, incorrect data format, or mismatched communication parameters such as baud rate, parity, stop bits, or data bits between the CNC and connected equipment.

Safety

Communication failed

Causes and Fixes

1
Navigate to SYSTEM > PARAM and verify RS-232C parameters: Check Parameter 20 (I/O channel selection), Parameter 101-102 (baud rate for channel 0/1), Parameter 110-111 (stop bits), Parameter 112-113 (parity settings), and Parameter 114-115 (data bits). Common settings are 9600 baud, 7 data bits, even parity, 2 stop bits.
2
Compare CNC parameters with the external device settings (PC, DNC software, printer). Ensure exact match for all communication parameters. For 0i/16i/18i series, verify Parameter 0020 bits 0-2 for I/O device selection.
3
If using Fanuc Ladder or PMC, check Parameter 904-919 for channel settings and verify the selected channel corresponds to the physical port being used (JD1A, JD1B connectors on control unit).
4
After correcting parameters, power cycle both the CNC and external device completely. Reset alarm and test communication with a simple program transfer or MDI operation.
Parameter changes require POWER OFF/ON cycle to take effect. Ensure Parameter Write Enable (PWE) is ON before modifying parameters.

DIY Feasiblehigh confidence

Call a technician if:

·Memory hardware failure confirmed
·Repeated failures after multiple memory clears
·System won't accept any programs after parameter reset

Prevention

Maintain regular parameter and program backups
Replace backup battery every 2-3 years
Avoid mixing programs from different Fanuc software versions
Use proper program transfer procedures with error checking

Common Mistakes

Not backing up parameters before memory clear
Ignoring low battery warnings
Loading programs created on newer software versions
Mixing different series program formats

Related Alarms

100 102 111 112

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