The FX465 is a 3-volt, half-duplex predictive Continuous Tone Controlled Squelch System (CTCSS) encoder/decoder microcircuit. The FX465 has integral voice-band filtering for prefiltering of Tx audio and the rejection of the CTCSS tone in receive. Under Processor control, the FX465 will encode and decode any one of 47 sub-audio frequencies (+NOTONE) in the range 67.0Hz to 254.1Hz. Tone frequencies and all functional commands can be loaded to the device in either pin-selectable 8-bit parallel or serial format.