piclist 1998\11\07\142748a >
Thread: VHF PLL controlled with PIC
picon face BY : Peter L. Peres email (remove spam text)

On Fri, 6 Nov 1998, Chris Eddy wrote:

{Quote hidden}

I did something with a MC145171, with and without extra UHF prescaler. The
only trick is to clean the data control lines from the PIC to the
PLL/synthesizer of RF if any is present (i.e. use RCs and proper
decoupling on the data lines). If you fail to do this strange errors can
happen sometimes. The PIC and the synth shared the same clock osc. which
was implemented at the Motorola part.

A PIC-only PLL is best done using a PWM ouput from a single pin followed
by a dumb RC low-pass. A transistor (or two) is (are) sometimes used to
chop a 33V voltage for larger tuning ranges (often used in un-syntesized
TVs). Of course the slow output filter must be accounted for in the PLL
loop to prevent instability. PLLs implemented like this with a PIC are
slow reacting as a rule (is there a rule ?).



In reply to: <3643BAC2.C864E638@nb.net>
See also: www.piclist.com/techref/microchip/math/filter.htm?key=pll
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