I would like to develop Bally Heck answer.
The EEC (non FADEC) is called a supervisory control system and contains all elements of conventional hydromechanical control plus an engine electronic control. Boeing required the system to be designed so that failures in the electronic portions are passive and result in no thrust change. In this event the hydromechanical control then assumes complete governing of the engine. The hydromechanical element govern basic engine operation (starting, accell, decel, speed governing, vane and bleed scheduling). The electronic control provides precision thrust management, rotor speeds limit protection and transmission of information for cockpit displays.
The supervisory control systems were certified on B767 with JT9D-R4 and CF6-80A engines in 1982. At that time Boeing judged that overall control system design and reliability had not yet been established to the point where a full authority digital engine control (FADEC) could be pursued for the initial 767 airplane. The 767 with PW4000,CF6-80C,RB211-524H FADEC controled engines were certified in 1988/1989.
The FADEC control doesn't employ any hydromechanical computations except for a mechanical overspeed governor. The control performs the following functions: starting, accell, deccel, speed governing, vane and bleed scheduling, engine operating and rating data; fault detection, isolation and acomodation by each of the two EEC channels and indication of fault status for display and maintenance. Flight crew commands required to control the engine are input to the EEC.
Mechanical thrust cable systems are not required with FADEC controllers.
The autothrottle computer (TMC) provides a trim command data word to each FADEC controller on the digital data buses between the units. Each FADEC controller reads it's own trim word and implements the requested change in power setting. The A/T computer adjusts the word, as necessary, to achieve equal thrust on all engines. The FADEC controller limits the magnitude of the received trim word so that a failure of the A/T computer can not cause a significant thrusth change on the engines.
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