Delta ASDA-B2 Fault AL020 Serial Communication Timeout

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Getting the AL020 fault on your Delta ASDA-B2 servo drive? Learn how to troubleshoot serial communication timeouts, adjust parameter P3-07, and verify your RS-485/RS-232 wiring.

Delta ASDA-B2 Fault AL020 Serial Communication Timeout

 

If you are using the Delta ASDA-B2 servo drive in an automated system, you may eventually encounter Fault AL020. This specific code stands for Serial Communication Time Out.

In simple terms, the drive has a "watchdog" timer. When it is controlled via a serial interface (like RS-485 or RS-232), it expects to hear from the controller (PLC, HMI, or PC) at regular intervals. If that "heartbeat" is missed for too long, the drive assumes the connection is lost and trips AL020 for safety. Here is how to diagnose and fix it.

Common Causes of AL020

The AL020 fault isn't usually a sign of a broken drive; it is almost always a configuration or physical connectivity issue. The primary causes include:

  • Aggressive Timeout Settings: The internal timer (Parameter P3-07) is set to a time shorter than the controller's communication cycle.
  • Physical Disconnection: A loose RJ-45 connector or a snapped wire in the communication cable.
  • Controller Inactivity: The PLC or HMI has stopped sending commands (perhaps it is in "Stop" mode or has its own internal error).
  • Electrical Noise (EMI): High-frequency interference is "scrambling" the data packets, making them unreadable to the drive.

Step-by-Step Troubleshooting Guide

1. Check Parameter P3-07 (Communication Timeout)

This is the most frequent culprit. Parameter P3-07 defines the maximum allowable time between received data packets.

  • The Fix: Navigate to Parameter P3-07.
  • If the value is very low (e.g., 100ms), try increasing it to 500ms or 1000ms to give the controller more breathing room.
  • Diagnostic Tip: Setting P3-07 to 0 disables the timeout detection entirely. While not recommended for final production safety, setting it to 0 is a great way to confirm if the issue is purely timing-related.

2. Inspect the Communication Wiring (CN3 Port)

Vibration in industrial cabinets can often loosen the pins in an RJ-45 or terminal connector.

  • Inspect the Cable: Check the cable plugged into the CN3 port on the front of the ASDA-B2 drive. Ensure the locking tab is clicked in firmly.
  • Verify Continuity: Use a multimeter to check for continuity on the Data+ (RS-485+) and Data- (RS-485-) lines. A single broken strand can cause intermittent timeouts.
  • Check the Pinout: Ensure you are using the correct pinout for Delta's serial interface (Pins 4 and 5 are typically used for RS-485 on the RJ-45 connector).

3. Verify the Master Controller (PLC/HMI)

If the drive is "listening" but the controller isn't "talking," the drive will eventually time out.

  • Check the Status LEDs on your PLC or HMI communication module. Are the "TX" and "RX" lights flashing?
  • Ensure the PLC is in RUN mode. If the PLC is stopped, it stops sending the cyclical commands the drive expects.
  • Verify that the Baud Rate (P3-01) and Communication Protocol (P3-02) on the drive match the controller exactly.

4. Eliminate Electrical Interference (Noise)

If AL020 occurs only when the motor starts or when a nearby machine turns on, you have a noise problem.

  • Shielding: Use a shielded, twisted-pair cable for your RS-485 link.
  • Grounding: Ensure the shield is grounded at the drive or controller end (but not both, to avoid ground loops).
  • Termination: If the drive is at the end of a long communication line, ensure a 120-ohm termination resistor is installed to prevent signal reflection.

Summary Checklist for AL020

Checkpoint Action Required
Parameter P3-07 Increase the value or set to 0 to test.
CN3 Connection Ensure RJ-45 is clicked in and wiring is tight.
PLC/HMI Status Verify the controller is actively sending data.
Baud Rate / ID Confirm P3-00 and P3-01 match the PLC settings.
Shielding Check for EMI if the fault is intermittent.

How to Reset the Fault

  1. Resolve the physical wiring issue or restore the PLC signal.
  2. Press the [Reset] button on the drive's keypad or toggle the Digital Input configured for "Alarm Reset."
  3. If the fault triggers again within seconds, the drive is still not receiving a valid command—re-check your Baud Rate and Station ID settings.

 

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