Byron A Jeff wrote:
> Again I'm confused. Presuming the signal is in the 15 Mhz range (67 ns period)
> and a PIC is running with a 5Mhz instruction clock (200 ns period), then even
> if such a chip existed, the finest resolution that the PIC could control the
> counter is at 3 count intervals, which is the number of ticks the counter
> would clock inbetween instructions. Right?
>
> Is the exact count necessary? Then you need something quite more complex that
> could be programmed with the amount of time to gate the incoming pulses along
> because the PIC isn't fast enough.
>
> If an exact count isn't necessary, then you simply prescale the count and let
> the PIC count it.
>
> But in any case the PIC's prescaler and count hardware is fast enough to
> handle the signal....
>
> BAJ

Well, its application requires a minimum counting of 15MHz, and it is
not
a pulse counter, but a frequency counter, what means it can stay holding
the counting as long it needs to read the shift register.

The counting gate is easily calculated with the PIC instruction
execution
time versus quantity of instructions, the common time loop, so it is
easy
to make a high precise counting gate even with a pic. Using a round
number
crystal frequency it will go to the crystal precision and accuracy.

There is another problem involved, I didn't say at the first post, the
pic
will serve just as an interface between the device that will make use of
the data and the 8 (yes, eight) counters like that working at the same
time.

The interesting point in here is that a simply 8 jk's fflops counter and
an
incorporated shift register could not cost more than $0.60, while it
would
be just the PIC crystal's cost.

A shift register with a "serial input pin" and "serial output pin" would
be great, since it allows to connect 8 or more chips in series, and at
the
reading time it just needs a string of clock pulses to transport all the
bits (bits per chip times number of chips), in a long string of bits.

In real, one can say it is a 8 or more bits counter with serial
interface,
probably found at the I2C or SPI chip library, but it doesn't exist.

--------------------------------------------------------
Wagner Lipnharski - UST Research Inc. - Orlando, Florida
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