Power Supply  and Clock Frequency

there are following  pins  for power  supply  and clock  frequency  signals.

V_CC + 5 V  power supply.

V_SS Ground reference

X₁ and X₂  these  two pins  are used  to connect  an external  crystal oscillator ( generally  RC clock Frequency) which is  responsible  to generate clock  frequency  for the systems.  For the  clock frequency  of the  microprocessor  to be 3  MHz the crystal should  have  the frequency  twice  of it i e  6 MHz as it is internally divided by two .

CLK  output - output clock  this is used  to provide  clock  signal  to other  ICs  used in the  same  systems  to synchronise them with  the microprocessor