The two low resistance n transistors at {TAIL ~ the same time} connect the data lines to {HEAD ~ ground} 
The two low resistance n transistors at { TAIL ~ the same time } connect the data lines to { HEAD ~ ground }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD