AS-i faults — slave address, 2-wire yellow power, how to diagnose

AS-Interface (AS-i) uses a flat 2-wire yellow cable carrying both power and signal for low-level sensors/actuators — cheap, simple. When a slave won't come up or the gateway faults, the cause is usually the slave address (duplicate/0), AS-i power, or yellow-cable wiring.

Common causes

1. Address 0 / duplicate — a replaced slave not yet addressed, or two slaves clash.
2. AS-i power — must use a dedicated AS-i supply (not plain 24V), voltage drop on long runs.
3. Yellow-cable wiring — piercing contacts not biting, reversed, poor contact.
4. Profile / config — master holds an old config, slave profile mismatch.
5. Too many slaves / length — over the segment limit (≈100m without a repeater).

Step-by-step diagnosis

1. Read the master LEDs The AS-i gateway shows config error / slave missing — tells you which slave is absent.
2. Set/fix the address Use an AS-i addressing unit to set the slave to the right number, avoiding 0/duplicate.
3. Measure AS-i power Confirm a dedicated AS-i supply, sufficient voltage at the farthest slave.
4. Check the yellow cable Inspect piercing points, correct orientation, contact; reseat suspect connectors.
5. Update the config Let the master “relearn” the configuration (store actual config) once correct.
6. Check the limits Slave count & segment length; add a repeater/extension if exceeded.

When to call an expert

AS-i is simple but address/power/wiring faults still stop machines. DeepDebug helps localize fast and reconfigure the master remotely, including AS-i ↔ Profibus/Profinet integration.