The MC145173 is a singlechip CMOS synthesizer with a fourwire serial interface for primary use in AMFM broadcast receivers. The device also finds use in longwave (LW) and shortwave (SW) receivers. Two inputs to a single highspeed N counter are provided, along with 2 phase detectors; one for a VHF loop up to 130 MHz, and another for an HF loop up to 40 MHz. The VHF phase detector has a current source/sink output and both detectors feature linear transfer functions (no dead zones). An external crystal ties across onchip circuitry which drives a completelyprogrammable reference counter. Thus, a broad range of tuning resolution is possible. The crystal oscillator is buffered and fed to an opendrain output which is active in the HF mode only. Due to the patented BitGrabberTM registers, address or steering bits are not needed in the serial data stream for random access of the registers. The serial port is byteoriented to facilitate control via an MCU. Tuning across a band is accomplished with a twobyte transfer to the N register. The 6bit analogtodigital converter (ADC) has two input channels. The converter is read via a onebyte transfer which includes an endofconversion (EOC) bit.