> I have a suggestion of something to add that will make it even more
useful.
> Track the times beween rising and falling edges, calc and store away a
> current velocity and acceleration value in a register somewhere, and send
it
> out as part of the poll.....i.e. edges per msec, and edges per
msec-squared.
>
> Thanks,
>
> - Ted

Ted,

This would typically be a part of the higher level software in whatever
device was polling the PIC.

BTW: here is a snippet of how C code would interpret the values coming back
from the poll. Note that the 16 bit counters in the PIC can overflow quite
quickly, so the next level of code has to handle the rollover intelligently.
It turns out that this is very simple to do.

long    pos1 = 0;       // assumed initial positions of encoders
long    pos2 = 0;

unsigned short last_count1 = 0;
unsigned short last_count2 = 0;
unsigned short last_faults1 = 0;
unsigned short last_faults2 = 0;

unsigned char new_faults1, new_faults2;


for (;;) // process forever
{
    unsigned short count1, count2;
    unsigned char faults1, faults2;

    // get the values from the encoder
    pollencoder( &count1, &count2, &faults1, &faults2 );

    // We compute the amount the count has changed. It turns out the
unsigned
    // arithmetic used below will properly handle the rollover cases. The
result of
    // the subtraction is cast to a signed value before adding it to the
current position
    // to compute the new position.
    pos1 = (short) (count1 - last_count1);
    pos2 = (short) (count2 - last_count2);
    last_count1 = count1;
    last_count2 = count2;

    // We compute the number of new faults, if any. Again, wraparound
arithmetic
    // does the right thing for us.
    new_faults1 = faults1 - last_faults1;
    new_faults2 = faults2 - last_faults2;
    last_faults1 = faults1;
    last_faults2 = faults2;

    if ( new_faults1 )
        report_faults( 1, new_faults1 );
    if ( new_faults2 )
        report_faults( 2, new_faults2 );
}

Bob Ammerman
RAm Systems

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