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Subject: Re: Crystal circuit

Date: 03/27/01 at 8:12 PM
Posted by: Greg Lynch
E-mail: fxrider@iname.com
Message Posted:

In Reply to: Re: Crystal circuit posted by John Dunn - Consultant on 08/17/00 at 9:09 PM:

I've got a parellel crystal circuit with a 74HCT04 IC.

The 18.432 MHz 18pf crystal is in parellel with a 100K ohm resistor across pins 1 and 2. Pins 1 and 2 have caps to ground, 27pf. Pins 2 and 3 tie together and clk is output on pin 4.

Can anyone point me to the math I need to replace the crystal with a 20pf?
It seems to matter.
Does this circuit oscillate at 18.432MHz?
Am I correct in that the 100K shunt resistor can be replaced by just about anything up to about 100 times greater?

I'd be glad to read and do the math myself but can't find the formulars or theory for these simple circuits.

Thanks for your time and thoughts.


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