When the value of {HEAD ~ the dc signal} equals or exceeds a predetermined value thereof, {TAIL ~ an indication} of tone detection is provided 
When the value of { HEAD ~ the dc signal } equals or exceeds a predetermined value thereof , { TAIL ~ an indication } of tone detection is provided
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH