On Thu, 11 Sep 1997 13:03:58 -0500 John Payson <supercat@MCS.NET> writes:
     pulse
     >>
     >> The PIC clock needs to synchronize to the incoming video, I was
     >planning
     >> to do that by using software to compare the sync pulses with the >state
     of
     >> the program, and output pulses to a varicap diode that adjusts the >>
     frequency of the PIC oscillator.  Anyone tried this before?  Just >>
     synchronizing the software will let the text jitter (maybe slowly, >maybe
     >> quickly) one pixel or so back and forth.  Also a custom crystal >would
     be
     >> required.  So I'd really like to synchronize the oscillator itself.
     ------------------------



     video in ->----------------------------------------->mixer----> video out
                 |                                          ^
                 |                                          |
                 v                                          |
               tv sync detector ic                          |
                H Sync   V sync                             |
                 |       |                            -----------
                 |       |                            |         |
                 |       \--------------------------->|         |
                 |                                    |         |
                 |                                    |  PIC    |
                 v                                    |         |
                PLL  --> vco --------------------->clk|         |
                 ^        |                           |         |
                 |        v                           -----------
                 |     divide by N *
                 |        |
                 |        |
                  \------/


     * Where N is (the number of PIC cycles desired per horizontal line) * 4

     Am I close??  Or completely in the weeds

     Joe