The FX589 is a single-chip modem employing Gaussian Minimum Shift Keying (GMSK) modulation. Data rates of 4kb/s to 64kb/s and the choice of BT to 0.3 or 0.5 are pin-programmable functions to suit radio data channel bandwidth requirements. The Rx and Tx digital data interfaces are bit-serial and synchronised to Rx and Tx data clocks generated by the modem. Separate Rx and Tx Powersave/Enable inputs allow for full- or half-duplex operation. Rx input levels can be set by a suitable ac and dc level adjusting circuit built, with external components, around an on-chip Rx input amplifier.