The 84021 is a general purpose, Crystal-to-LVCMOS/LVTTL High Frequency Synthesizer. The 84021 has a selectable TESTCLK or crystal input. The VCO operates at a frequency range of 620MHz to 780MHz. The VCO frequency is programmed in steps equal to the value of the input reference or crystal frequency. The VCO and output frequency can be programmed using the serial or parallel interface to the configuration logic.