In a message dated 24/07/1997  17:36:25, you write:

<<
   Vdd is power supply , Vss is ground but what is Vpp ?? It is in the
 documents of Serial Programming a Pic16C84 . A pin of Pic chip ???
  >>

It is the programming voltage  applied to pin labeled MCLR (normally) when
the PIC is in programming mode.

Francesco