The FX365C is a 3-volt, half-duplex predictive Continuous Tone Controlled Squelch System (CTCSS) encoder/decoder microcircuit. The FX365C has integral voice-band filtering for prefiltering of Tx audio and the rejection of the CTCSS tone in receive. Under Processor control, the FX365C will encode and decode any one of 39 sub-audio frequencies (+NOTONE) in the range 67.0Hz to 250.3Hz. Tone frequencies and all functional commands can be loaded to the device in either pin-selectable 8-bit parallel or serial format.