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'20 MHz Ceramic Resonators'
I spoke with Jim Simmons at Microchip about using a 20MHz resonator on a PIC
(16C621), and he told me that many people were not able to make this work,
but he had spoken with one customer that hadn't had any trouble with his
particular brand; unfortunatly Jim could not remember what brand it was that
worked. Has anyone discovered a working, reliable 20MHz resonator solution?
Also, anyone have any thoughts on whether or not a 20MHz resonator would be
good for reliable 9600 Baud serial communication?
E-Lab Digital Engineering, Inc.
| We've been using 16 MHz on the 16c74. To save board space, we
went with resonators with internal capacitors. The Microchip data book
gives a muRata resonator number for 16 MHz, but not 20 MHz. The part
number they do specify uses external capacitors of 10 to 22 pF. The
resonators with internal capacitors (muRata, ECS and Integrity) all have
30 pF capacitors in them. With ECS and Integrity, we've had between 30
and 50% of the resonators not start. We've only tried 6 of the muRata
with internal capacitors, and they all worked. muRata tells me they are
currently working with Microchip on characterizing resonators to work
with the chips. This work is going on in Japan. Earlier this week ECS
told me that they'd get some Microchip chips and see what's going on.
Integrity told me that if the resonators work with a standard inverter
circuit, the resonators are ok. They probably are, but we're not using a
standard inverter! Also, Microchip was unable to give me details on the
oscillator in the 16c74 (such as an input Z plot, output Z plot, and gain
plot, all with both magnitude and phase). So, we're kinda stuck just
plugging in resonators and see who gets the highest score! The next
production run we'll try muRata.
We are using the 16 MHz resonator and getting good 250 Kbps
transmit and receive operation out of the uart. The tables in the
databook indicate you can get 9.6 Kbps -1.36% with a 20 MHz clock and
+0.16% wit a 16 MHz clock.
On Wed, 26 Mar 1997 16:45:40 -0600 Todd Peterson <NETINS.NET> elab
'20 MHz Ceramic Resonators'
|In message <netins.net> 22.214.171.12470326163556.3aafef0cMITVMA.MIT.EDUPICLIST
> I spoke with Jim Simmons at Microchip about using a 20MHz resonator on a PIC
> (16C621), and he told me that many people were not able to make this work,
> but he had spoken with one customer that hadn't had any trouble with his
> particular brand; unfortunatly Jim could not remember what brand it was that
> worked. Has anyone discovered a working, reliable 20MHz resonator solution?
> Also, anyone have any thoughts on whether or not a 20MHz resonator would be
> good for reliable 9600 Baud serial communication?
I have used what I believe to be a Murata 3 terminal resonator on
a 16C73 with no problems. The part number is CST20.00MXW.
It was used on an early prototype, but was repalced after a number
of weeks with an oscillator, so I can't comment on whether it works
with different batches of PICs and resonators.
Regarding rs232 comms, I have used a 4MHz resonator to bit bash
rs232 transmission and reception on a 16C84 with no problems.
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