Each of {HEAD ~ the EDUs}, {TAIL ~ keypad controllers} and CCIs of the system is connected to a common communication bus 
Each of { HEAD ~ the EDUs } , { TAIL ~ keypad controllers } and CCIs of the system is connected to a common communication bus
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH