RE: where to get parts?

> 1) An oscillator is a crystal with supporting components to make the
> signal digitally TTL compatible
>
Yup. I'd be a little careful with the "TTL" designation, but "logic
level" is probably a safe statement. (I don't know if you can get
oscillators that run at less than 3V, but probably for a price they
exist...)

> 2) Multiply the fundamental by overtone to get MHz (if it's an
> overtone
> crystal)
>
Usually overtone crystals are listed by the frequency when operated in
the overtone mode. The important thing to know is that a "3rd overtone"
crystal may or may not work properly in a circuit unless the circuit is
designed for the 3rd overtone crystal to begin with. (Since the crystal
manufacturer's are getting better all the time it's possible to have
fundamental and overtone crystals in the same frequency band. The
"gotcha" is that using an overtone crystal in a ciruict designed for a
fundamental (and vice-versa) might not work.)

(We had some proto boards here give us problems-- we were using 29MHz
fundamental crystals. We accidentally got a few boards with 3rd
overtone crystals on them. Sometimes they'd start up at ~9MHz,
sometimes they'd run at 29MHz... Really flakey.)

-Clay
Received on Tue Jan 19 12:41:11 1999