Thanks for the fast responces to my questions ,THREE TWENTY and SILKY.
Just the information I was looking for .
Im I right in saying the A/TH is arm on on the ground when you select the A/TH switch on the FCU to arm the system.
The system is not active until you bring the thrust levers back to CLM at the thrust reduction altitude.
So putting the s/w to arm engages the system but it can be active or not active depending on the thrust levers position , and flight envelope protections.
To disconnect the system you can operate the levers disconnect button or the FCU switch
Have I got the right understanding now?