What causes FANUC alarm 085?

Baud rate set too high for reliable communication with the sending device. Communication cable too long or not properly shielded, causing signal degradation. Fanuc serial parameter settings (baud rate, stop bits, parity) do not match the external device. External computer sending data faster than the control can buffer it (no hardware handshaking). Faulty RS-232 interface board in the CNC control unit.

How do I fix FANUC alarm 085?

1. Reduce the baud rate on both the CNC and external device to a lower value (e.g., 4800 or 9600 baud). 2. Verify the serial communication parameters match exactly on both ends (baud, data bits, stop bits, parity). 3. Enable hardware handshaking (RTS/CTS) on both devices if supported. 4. Check the cable length and shielding — RS-232 is limited to approximately 15 meters. 5. Test with a known good cable and a different computer if the problem persists.

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FANUC Controller

Program/G-code · Intermediate · 15-30 minutes

Alarm 085

Fanuc Alarm 085 - OVERRUN ERROR

Fanuc Alarm 085 (Communication Timeout) indicates the CNC has failed to receive expected data from an external device within the programmed timeout period. This typically occurs during serial communication (RS-232C, HSSB, Ethernet) between the CNC and peripheral equipment such as DNC systems, robots, PLCs, or bar feeders. The alarm triggers when handshake signals are not received or data transmission is interrupted beyond the timeout threshold defined in communication parameters.

FANUCProgram/G-codeIntermediate15-30 minutes

085

Fanuc Alarm 085 - OVERRUN ERROR

OVERRUN ERROR

Root Cause Summary

Fanuc Alarm 085 (Communication Timeout) indicates the CNC has failed to receive expected data from an external device within the programmed timeout period. This typically occurs during serial communication (RS-232C, HSSB, Ethernet) between the CNC and peripheral equipment such as DNC systems, robots, PLCs, or bar feeders. The alarm triggers when handshake signals are not received or data transmission is interrupted beyond the timeout threshold defined in communication parameters.

Safety

Data transfer failed

Causes and Fixes

1
Navigate to SYSTEM > PARAM and verify parameter 0020 (baud rate: 0=300, 4=4800, 5=9600, 6=19200), parameter 0021 (stop bits: 0=1bit, 1=2bits), and parameter 0022 (parity: 0=none, 1=odd, 2=even) match the external device settings.
2
Check parameter 0000 bit 0 (I/O channel selection) and parameter 0020 bit 2 (TV check) settings. Verify parameter 0101 (timeout value) - increase from default if network latency is high, typical range 1-60 seconds.
Changing parameter 0000 requires power cycle to take effect
3
Verify parameter 0112 (DC code settings) and parameter 0110 (end-of-block code). For DNC operations, confirm parameter 0100 bit 0 (EIA/ISO code) matches the data format being transmitted.
4
Test communication by navigating to SYSTEM > I/O and attempting manual data input/output. Monitor DIAGNOSIS > I/O for real-time communication status and handshake signal states (DR, ER, SR).

DIY Feasiblehigh confidence

Call a technician if:

·I/O board hardware failure suspected
·Parameter changes don't resolve issue
·Multiple communication alarms occurring

Prevention

Regularly inspect RS-232C cables for wear
Document working communication parameters
Use surge protection on communication lines
Avoid hot-plugging RS-232C connections

Common Mistakes

Forgetting to restart CNC after parameter changes
Using straight-through cable instead of null modem
Mismatching baud rates between devices
Ignoring handshaking requirements

Related Alarms

086 087 088

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