--- In BITX20@..., Jim Strohm <jstrohm@e...> wrote:
On Jul 10, 2005, at 7:04 AM, Ashhar Farhan wrote:
while PLL chips are difficult to find, the 16F84 or the 16F628 are
plentiful. why can't we program the PIC to behave as a PLL on it's
own?
the PIC timer can be used to accurately measure the oscillator
frequency
(as normal PIC based frequency counters do) instead of displaying the
frequency on a display, it can (in addition) also pump a capacitor
that
in turn is used to bias a varactor across the VFO.
if chris and his merry band can do a single chip HnP, there is no
need to
assume that they can't turn out a single mirochip PLL too.
Given how cheap a PIC is, I think it's just a matter of time before
we stop using standard TTL/CMOS logic, and start programming PICs as
replacements. They won't be pin-for-pin replacements, but they'll be
easier to locate than some of the more esoteric logic chips.
A PIC PLL sounds like a fabulous project.
Jim N6OTQ
Three things:
PIC is a sequential device, there are whole classes of logic solutions
that are not easily done with a sequential device.
Using the PIC as a PLL, it could be done but even the fastest parts
are far too slow to be succiciently precise. With PLLs a lack of
precision can be causes noise in the signal. The core of most PLLs
is the phase detector which is usually a very fast sequential logic
element to in real time compare the phse of two signals. Hard to do
well enough with a PIC.
Using a PIC for HnP and display, this is very do able.
Allison
KB1GMX
