The second control signal is coupled to {HEAD ~ an input} of {TAIL ~ the NAND gate} and inactivates the first control signal 
of
The second control signal is coupled to { HEAD ~ an input } of { TAIL ~ the NAND gate } and inactivates the first control signal
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH