Presettable tuning apparatus

Abstract

A presettable tuning apparatus includes a digital tuner; a source of digital signals representing radio frequencies to which the tuning apparatus is respectively tuned; an addressable memory having a plurality of sequentially addressable storage locations therein for storing selected ones of the digital signals; write-in circuitry for selectively writing the digital signals from the source into selected ones of the storage locations in the memory; a comparator circuit for comparing the digital signals stored in an adjacent pair of the sequentially addressable storage locations and providing a control signal indicating the relative values of the frequencies represented by such digital signals; and circuitry for replacing the digital signals stored in the pair of storage locations with one another when the control signal indicates that the frequency represented by the digital signal stored in the lower-address one of the pair of storage locations is higher than that represented by the signal stored in the higher-address one of the pair. The apparatus thereby automatically rearranges the particular storage locations in which the digital signals are stored so that the order of the frequencies represented thereby corresponds to the sequential order of the storage locations, notwithstanding that the digital signals can be written at random into the addressable memory.