Michel Tremblay's recent thought provoking thread on synchronizing a PIC
to within one instruction to an external clock makes me wonder if it is
possible to sample an arbitrary wave form with single cycle resolution.
The best I think you can do (without using external hardware) is two
cycle resolution. For example, assuming that our sample is at PORTB <0>
the following code will work:


buffer0 EQU     0x20             ;RAM buffer
buffer1 EQU     buffer0+1        ;Allocate enough for all the bits
  .                              ;to be collected
  .
  .

SAMPLE
        RRF     PORTB           ;Sample PortB <0> by shifting it into C
        RRF     buffer0,F       ;Save the sample in RAM
        RRF     PORTB
        RRF     buffer0,F
        RRF     PORTB
        RRF     buffer0,F
        RRF     PORTB
        RRF     buffer0,F
        RRF     PORTB
        RRF     buffer0,F
        RRF     PORTB
        RRF     buffer0,F
        RRF     PORTB
        RRF     buffer0,F
        RRF     PORTB
        RRF     buffer0,F       ;Now have 8 samples

        RRF     PORTB           ;Start on the next 8 samples
        RRF     buffer1,F
        RRF     PORTB
        RRF     buffer1,F
   etc... for six more samples, and repeat the pattern...


Does anyone else have any better ideas?


Scott

P.S. Michel, I didn't know you wanted a phase locked loop! But I like the
"synch" solution none-the-less.