Cause : XSTO circuit open comes when circuit connected to XSTO:IN1 and/or XSTO:IN2 is open. The XSTO circuit provides a way to stop the drive operation through external control. This is important for safety and system integration. The circuit typically consists of two terminals, XSTO:IN1 and XSTO:IN2, where an external signal can be applied to trigger a drive stop.

The fault code 5E03 in your ABB ACS880 drive indicates an issue with the XSTO circuit. This circuit is responsible for external stop control, which allows you to stop the drive using an external signal from a separate control system or safety device.