Reply by " [msp430]" June 23, 20182018-06-23
Thank you for both quick replies - much appreciated.

I now understand that there is greater variability unit-to-unit than I assumed, however, this it not a problem, just requires that I include a mechanism for determining then storing in information flash the required unit-specific constants.



On Thu, 6/21/18, wrote:

Subject: [msp430] Digest Number 5229
To: m...
Date: Thursday, June 21, 2018, 9:04 PM

There are 2 messages in this issue.

Topics in this digest:

1a. Re: Consistency of DCO parameters
across multiple samples of a given   
    From: Onestone

2. Re: Consistency of DCO parameters
across multiple samples of a given   
    From: Fedde Bloemhof

1a. Re: Consistency of DCO parameters
across multiple samples of a given
    Posted by: "Onestone"
    Date: Wed Jun 20, 2018
8:29 pm ((PDT))

The accuracy and repeatability of the
DCO  clock for the pre-programmed
values is around 3%. I tested just 20
samples and found that typically
this was closer to 1%. Certainly on a
range of 200 shipped units, using
a calibrated DCO for a 460kb UART, no
complaints were received regarding
failed communication to a PC based
program. But this is a small sample.
For any other value of DCO frequency I
would expect much worse, given
that Ti rate some of their calibrated
values as worst case +/-6% over
the full temperature range.  What
prevents you from using one of the
calibrated frequencies, or even a cheap
watch crystal. Not all, but
most, of my designs use a watch
crystal, and still achieve very low mean
power consumption, and I design very
tiny systems typically 1cm square
or smaller, so size shouldn't be an


On 21/06/2018 9:01 AM, David Feldman
[msp430] wrote:
> I am working on a project that
uses MSP430G2452IPW14 (14 pin TSSOP package.)
> At initialization, I set MCLK and
SMCLK sourced from DCO and set DCO to my chosen clock
frequency (I did not rely on Info flash segment D
calibration parameters, as those didn't yield the frequency
I require.)
> I was surprised to find upon
building my second prototype of the project that the DCO
frequency, using the same parameters as the first prototype,
was off considerably (perhaps 5% or so.)
> What should I expect in terms of
DCO frequency consistency? Should I plan a calibration step
for each device I use (i.e., find it's correct parameters to
obtain the required frequency?) I do not have a crystal or
other primary frequency source in the design -- the DCO is
being used stand-alone with no discipline mechanism
> Thanks,
> Dave

> Posted by: David Feldman

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