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