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




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Reginald Beardsley p...@yahoo.com [msp430] wrote:
> I'm seeing more jitter than I would like in the length of a pulse (e.g. 120 us) generated by timer A in PWM mode using ACLK from the 32 KHz xtal on a G2553 Launchpad. An eyeball estimate is a standard deviation of 15 ns. I've pulled the header pins that connect to the xtal and removed the zero ohm jumpers. That improved things a lot, but I'd like better if possible. Is there anything else I should consider?
>
> This is plugged into a solderless breadboard with a 10x scope probe connected to a short wire plugged into the row for P1.6. LED2 is disconnected.
>
> Is it reasonable to think that I can improve on this with the Launchpad? I found a Freescale application note showing jitter well under 1 ns using a 32 KHz xtal feeding the PLL to generate 48 MHz USB timing. This leads me to think it's a noise issue with the Launchpad design or my bench area (several computers running) in close proximity), but I could be all wet.

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: Dan Bloomquist




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I'm seeing more jitter than I would like in the length of a pulse (e.g. 120 us) generated by timer A in PWM mode using ACLK from the 32 KHz xtal on a G2553 Launchpad. An eyeball estimate is a standard deviation of 15 ns. I've pulled the header pins that connect to the xtal and removed the zero ohm jumpers. That improved things a lot, but I'd like better if possible. Is there anything else I should consider?

This is plugged into a solderless breadboard with a 10x scope probe connected to a short wire plugged into the row for P1.6. LED2 is disconnected.

Is it reasonable to think that I can improve on this with the Launchpad? I found a Freescale application note showing jitter well under 1 ns using a 32 KHz xtal feeding the PLL to generate 48 MHz USB timing. This leads me to think it's a noise issue with the Launchpad design or my bench area (several computers running) in close proximity), but I could be all wet.

Thanks,
Reg


Posted by: Reginald Beardsley




Start a New Thread