the second device is driven by the second power supply, and capable of performing a communication via the bus in the condition in which the pull up {HEAD ~ voltage} is equal to {TAIL ~ the second predetermined voltage}, wherein 
is equal to
the second device is driven by the second power supply , and capable of performing a communication via the bus in the condition in which the pull up { HEAD ~ voltage } is equal to { TAIL ~ the second predetermined voltage } , wherein
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH