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