Re: Launchpad clock jitter: What should I expect?

"Reginald Beardsley [email protected] [msp430]" <[email protected]> Wed, 25 Feb 2015 16:22:23 -0800
Newsgroups gmane.comp.hardware.texas-instruments.msp430.discuss
Message-ID <[email protected]>
Dan,

I've got the pins soldered into the underside of the  Launchpad so it plugs into a breadboard.  I had huge issues w/ XOUT and XIN last summer until I removed the pins and the jumpers.  Before I did that, the jitter was over 1 us which was terrible.  I'm not using the TEST pin.  A scope probe on that shows  100-150 mV noise bursts at the transitions on P1.6, but I'm pretty sure that's just stray pickup by the probe.  A 100 nF capacitor to ground on TEST really doesn't change things.  My instincts are that the jitter is caused by noise pick up at the xtal connections, but I'd love to have confirmation from someone with more experience.  If it is the result of noise on the xtal lines, then it's a design limitation of the board and I'll have to live with it or use another board like the F5529 
 Launchpad.

I'm running Mecrisp forth, so the debugger doesn't enter into it.  I can sit and change the running timer settings via a commandline terminal like God intended ;-)

Have Fun!
Reg

--------------------------------------------

 
 Hi Reg,
 
 I had recently worked with the same device using the FET.
 Same, I wanted 
 
 the chip on a breadboard, not the launch pad. I had a pretty
 rough time 
 
 with the 32k xtal while debugging. I found that the noise
 from the TEST 
 
 pin was all over the XOUT, and sometimes even keeping the
 clock from 
 
 running. I'd bet that without the debugger and using the
 ACLK out to 
 
 check the clock will be stable. And for anyone that runs
 into the clock 
 
 not running while debugging, I found that a 56pF on XOUT to
 ground keeps 
 
 the TEST noise down so it works.
 
 
 
 Best, Dan.
 
 


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Posted by: Reginald Beardsley <[email protected]>
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