Sidesticks are spring-loaded to neutral. When the autopilot is engaged, a solenoid-operated detent stiffens both sidesticks in the neutral position.
If the pilot applies a force above a given threshold, the autopilot
disengages and the sidesticks operate under normal artificial feel loads
and sends an input to the computers.
The hand grip includes 2 P/Bs: An autopilot disconnect/sidestick priority P/B and a push-to-talk button.
Sidestick priority logic: When only one pilot operates the sidestick, his
demand is sent to the computers. When the other pilot operates his
sidestick, in the same or opposite direction, both pilot inputs are
algebraically added. The addition is limited to single-stick maximum
deflection.
NOTE: In the event of simultaneous inputs on both sidesticks (2°
deflection off the neutral position in any direction), the two
green SIDE STICK PRIORITY lights, on the glareshield, come
on and the “DUAL INPUT” voice message activates.
A pilot can deactivate the other sidestick, and take full control by pressing
and keeping pressed his takeover P/B. For latching the priority condition,
it is recommended that the takeover P/B be pressed for more than 40
seconds. The takeover pushbutton can then be released without losing
priority.
However, a deactivated sidestick can be reactivated at any time,
by momentarily pressing either takeover P/B. If both pilots press their
takeover P/Bs, the last pilot to press their P/B will have priority.
NOTE: If an autopilot is engaged, any action on a takeover P/B will
disengage it.
In a priority situation, a red light will come on, in front of the pilot whose
sidestick is deactivated. A green light will come on, in front of the pilot
who has taken control, if the other sidestick is not in the neutral position
(to indicate a potential and unwanted control demand).
NOTE: If one stick is deactivated on ground, at takeoff thrust
application, the takeoff «CONFIG» warning is triggered.
Source – Airbus