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For what purpose will you use a 4046 with th 16F877 ?
A phase locked loop is used to synthesize frequency, i.e. multiply frequency. Some PICs have an internal PLL to multiply the frequency of a crystal to be used as a main clock. If it is the case, the 4046 has a maximum operating frequency output of 1MHz @ Vdd = 5V, which is too low for the PIC clock (you can use a 20MHz crystal directly).
If it is not the case and you just try to multiply the frequency of a signal from PIC, just connect the signal to pin 14 (signal in) of 4046, choose pin 2 or 13 for phase comparator, you should calculate a RC low pass filter (to pin 9), choose some componentes to VCO (Capacitors and resistors), use a frequency divider counter (between pins 3 and 4). Better take a look at the 4046 datasheet (search at Philips site).