A/c ATC Transponder
 

If its a transit flight, should the ATC transponder with an stdby/auto/on function be set to stdby or keep it at auto for parking, squawking 2000. Will keeping it at AUTO interfere with ATC during the time a/c is on ground with engines shut down or will it automatically switch to stbdy mode with any internal logic. On ground in AUTO it goes to mode S. The QRH for the A320 says stdby. I follow what the QRH says but its a doubt I'd like to clear.

Cheers

Once you have stopped at the gate and shut down you should switch to standby, and leave it there until you start moving again for departure.

Good thought! I've had a few guys over the years leave it in "Auto" only to have a few ATC units (Bangkok and Hong Kong come to mind) remind us the set it to "On," rightfully so, per their airport requirements (Ground Radar, etc). So, it would seem that in "Auto" with the aircraft on the ground (Airbus), it reverts to "Stby".

Depends on the aircraft. Some systems switch to standby on their own, others don't. In some airports, one is expected to have the transponder on for taxi for ground radar purposes, and in other locations, one is not. Do what is appropriate according to the aircraft, the equipment, and the location.