Re: Launchpad clock jitter: What should I expect?

I have seen influence of mechanical vibration on the 32kHz xtal (knock on 
it with the finger und you see terrible waves on the scope!).
Is the case of the xtal grounded? TI recommends soldering of the case of 
the XTAL to GND. 

Matthias

"Reginald Beardsley pulaskite-/[email protected] [msp430]"
<[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.
>  
>  
> 
> 
> ------------------------------------
> Posted by: Reginald Beardsley <pulaskite-/[email protected]>
> ------------------------------------
> 
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> 
> 
> 




------------------------------------
Posted by: Matthias Weingart <[email protected]>
------------------------------------

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