What causes FANUC alarm 102?

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 102?

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 102

Fanuc Alarm 102 - Buffer Overrun

Alarm 102 occurs when the CNC control cannot process incoming serial data fast enough, causing the receive buffer to overflow. This is typically caused by excessive baud rate settings, incorrect communication parameters, or hardware issues with the RS-232 interface preventing proper data flow control.

FANUCCommunicationIntermediate15-30 minutes

102

Fanuc Alarm 102 - Buffer Overrun

Overrun Error

Root Cause Summary

Alarm 102 occurs when the CNC control cannot process incoming serial data fast enough, causing the receive buffer to overflow. This is typically caused by excessive baud rate settings, incorrect communication parameters, or hardware issues with the RS-232 interface preventing proper data flow control.

Safety

Data lost

Causes and Fixes

1
Check parameter 20 (baud rate setting) on the CNC and verify it matches the external device exactly. Common values are 4800, 9600, or 19200 baud.
2
Reduce baud rate to 4800 or 9600 baud on both CNC and external device if currently set higher.
Record original parameter values before making changes.
3
Verify parameter 21 (stop bits), parameter 22 (parity), and parameter 19 (data bits) match between CNC and external device.
4
Test communication by sending a small program file (under 10KB) and gradually increase file size if successful.

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