The MC145149 contains two PLL Frequency Synthesizers which share a common serial data port and common reference oscillator. The device contains two 14stage R counters, two 10stage N counters, and two 7stage A counters. All six counters are fully programmable through a serial port. The divide ratios are latched into the appropriate counter latch according to the last data bits (control bits) entered. When combined with external lowpass filters and voltage controlled oscillators (VCOs), the MC145149 can provide all the remaining functions for two PLL frequency synthesizers operating up to the device's frequency limit. For higher VCO frequency operation, a down mixer or dualmodulus prescaler can be used between the VCO and the synthesizer IC.