crystal oscillator for system clock?

[agraupe]

Posted on January 24, 2005 at 10:09

crystal oscillator for system clock?

[agraupe]

Posted on May 17, 2011 at 12:05

Is it a good idea to drive a schmitttrigger by the XTAL2 output of the crystal-oscillator to get a dividable system clock for other peripherals?

I would like to use a 22.1184 crystal or a 40Mhz crystal on a uPSD3334D-40T6.

Do you have any design ideas for me please

Greetings

[jdaniel]

Posted on May 17, 2011 at 12:05

Andy,

In general it's a bad idea to throw anything into the feedback loop for the oscillator that could affect the resonance. For instance, you'd have to adjust the load capacitor on that side to take into account the input capacitance on the schmitt trigger. Also, if you've ever looked at the clock signal with a scope, they tend not to be at all a square wave and you'd have to make sure your scmitt trigger would work properly with what it's putting out.

I don't know if you've already decided on using the -40T6 package for this part yet or not, but if you instead used the TQFP80 package (-40U6), then you could use the ALE signal which will basically give you a divided version of the clock with the capability to easily drive a scmitt trigger. That's assuming you're not using any external memory, but then, if you weren't even going to have the address bus on there before, I'm thinking that's a safe assumption.

Hope some of that helps.