From memory, the EEC's have Prim & Sec computation sections that only use data from local sensors to do all its own calculations, only if there is a internal voting error does the EEC look at A/C data, Prim at L ADC & Sec at R ADC. If there is an error with external data, the EEC will use internal generated assumed data using the local sensors available to it. Not too sure off hand if this is RR or GE or both (similar).
SC, you're memory is good but just a little off. All of the 'electronic' engines i've worked on GE CF6, RB211-524 and P & W 7R4 and PW4000 all use the ADC inputs for TAT, MACH and P0 (ambient press).
Yes, they all have their own built-in engine sensors for these parameters but only default to these if the ADC input is lost and/or is outside of the EEC's internal error checking limits (i.e the EEC takes the ADC input for say P0 and checks it against it's own P0 sensor - if the two figures are within an acceptable tolerance the ADC data is the one used for calculations by the EEC)
As was explained to me by a very good instructor, more money is spent on the building/testing/certification of the ADC's and this data is good enough to operate the auto-pilot, displays for pilots, ATC encoder etc, so it's the best info for the engines to use too.
Of course the engine EEC's need other parameters NOT measured by the ADC's so in those cases use attached engine sensors.
P.S. will dig into the books and see if I can find some more info.
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