a pull down unit which pulls down the output terminal of {HEAD ~ the data transfer unit} in response to an output signal from {TAIL ~ the second logic unit} 
a pull down unit which pulls down the output terminal of { HEAD ~ the data transfer unit } in response to an output signal from { TAIL ~ the second logic unit }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL