{HEAD ~ a second logic unit} which logically operates {TAIL ~ the first data} and the second transfer control signal, and outputs the result of the logical operation; and 
logically operates
{ HEAD ~ a second logic unit } which logically operates { TAIL ~ the first data } and the second transfer control signal , and outputs the result of the logical operation ; and
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH