The frequency reference input is selectively at one of {TAIL ~ a first or second fixed voltage} of {HEAD ~ level} designating respectively a first or second oscillator frequency, and a variable signal designating an oscillator frequency 
The frequency reference input is selectively at one of { TAIL ~ a first or second fixed voltage } of { HEAD ~ level } designating respectively a first or second oscillator frequency , and a variable signal designating an oscillator frequency
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH