take a look at shop manuals, if your local library has them (manufacturer's manuals if you can find them, not Chilton's etc., although Chilton makes a manual just for Electronic Controls).

my 79 Pinto had a single ECU that i know of (the case might have a dual redundant processors inside it, but i doubt it).

93 Geo Prizm (Toyota Corolla is a sister vehicle and should be similar) has separate ECUs for (at least): ECM - Engine Control, EBCM - Brakes (ABS), SRS - Airbag, PCM - Powertrain (Transaxle), CCM - Cruise Control. the Engine Control Module and the Powertrain Control Module are combined in one case, with separate connectors. these controllers are distributed behind the center column and under the passenger-side kick panel (floorplate against the firewall), except for the SRS module which is on the steering column. (i think that on the pinto the ECU was in the engine compartment, but i'm not sure.) ECM, PCM, SRS, CCM, and ECBM have their own sets of error codes and diagnostic flowcharts. there is a Power Door Lock Control Module, but i don't see much on it, maybe it is discrete.

no mention of WHICH mcu flavors (no service procedures are given for the insides of the modules; just "Replace ___ Module" ).

there is a Center Sensor Assembly but it looks like discrete components. the two wires between the CSA and the SRS (Airbag module) have three "shorting bars" along their length: "To prevent accidental deployment, shorting bars close to short terminals when the connector halves are separated." (at the CSA and at the Upper and Lower Steering Column Connectors). i remember that the SRS has several interlocks; for example, if you disconnect (or leave disconnected) the instrument panel while the power is on (or toggled on) the SRS will not detect the Airbag lamp and will disable itself until you've flushed the error code (hopefully following the diagnostic procedure so it wasn't a different problem). and the whole manual is sprinkled with warnings to read the SRS (Airbag) section before servicing electrical components or working around SRS components.

james