Upon receiving a compel data command, a function block of {TAIL ~ a device} publishes its output data on {HEAD ~ the bus} 30 
Upon receiving a compel data command , a function block of { TAIL ~ a device } publishes its output data on { HEAD ~ the bus } 30
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH