a first diode disposed in series between the first power supply and {HEAD ~ the signal line} so as to allow supply of the pull up voltage from the first power supply to the signal line and to block {TAIL ~ flow} of a current from the second power supply to the first power supply, 
to block
a first diode disposed in series between the first power supply and { HEAD ~ the signal line } so as to allow supply of the pull up voltage from the first power supply to the signal line and to block { TAIL ~ flow } of a current from the second power supply to the first power supply ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH