420, from the company provided FCOM1 CD:
AUTO FLIGHT FLIGHT GUIDANCE
A/THR ARMING CONDITIONS 1.22.30 P60
or
AUTO FLIGHT FLIGHT GUIDANCE
1.22.30 P63
Caution - If the pilot pushes and holds one instinctive disconnect pushbutton for more than 15 seconds, the A/THR system is disconnected for the remainder of the flight. All A/THR functions including ALPHA FLOOR are lost, and they can be recovered only at the next FMGC power-up (on ground).