A multiplexer, selectively couples {HEAD ~ data} from either the main memory device or the shadow memory device to {TAIL ~ an output terminal} in response to a control signal 
to
A multiplexer , selectively couples { HEAD ~ data } from either the main memory device or the shadow memory device to { TAIL ~ an output terminal } in response to a control signal
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH