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