Engines are rated based on weight and elevator/rudder control limits which can be then derated by the owner via EEC plugs.
The top rating of the engine is the max thrust you can expect to get at fire wall position of the thrust levers...for example a CFM56-7B can provide 27400 lbs of torque up to its Tref.
EEC doesnt calculate the rating,it knows the rating already but it calculates the Max N1 TRA and provides it to the AT.
So as per this above definition on A/T Limit, during normal operation the A/T system uses N1 limit values ( the N1 reference bugs which are placed on the N1 gauge) from the FMC, and during a degraded operation it uses a degraded N1 thrust from the related EEC
Correct.
Isn't this a conflict? Because EEC when in ON posn (which is the normal mode) provides the engines rating or places the Reference N1 bugs on the N1 gauage, but the A/T LIM defenition says A/T system takes input from EEC in a degraded mode, and in normal mode it takes input from FMC
The autothrottle is providing the N1 limits if the FMC N1 data is invalid for climb,cruise and Go Around but Not for take off.
The n1 cursors can be used but are fo reference only and you would get dashes on the TMA as the FMC isnt providing the info.