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ADC10 results ok in JTAG, different in standalone run

Started by hc08jb8 December 16, 2004
Hello Guys

I have a strange problem, I am logging pressure sensor data using 
F1232 via its one of the ADC channel. When the pressure sensor is 
stable, I get a 0.69V~0.71V (i.e. no presssure applied). This works 
as expeced when debuggin in JTAG mode.

However when I run the same code standalone, the ADC reading for the 
same case is fluctuatig (0.69V~0.80V). The only difference is that I 
have detachted the JTAG cable, what could be wrong, where should I 
start looking into? Any ideas?

Cheers
Jay






Beginning Microcontrollers with the MSP430

Hi Jay,

hc08jb8 wrote:
> However when I run the same code standalone, the ADC reading for the
>  same case is fluctuatig (0.69V~0.80V). The only difference is that I
>  have detachted the JTAG cable, what could be wrong, where should I 
> start looking into? Any ideas?

Noisy power supply, attach the scope.

Indrek

-- 
  Indrek Rebane           |      Borthwick-Pignon
  Electronics Engineer    |    Tartu Science Park
  Phone: (+372) 7 302 641 | Riia 185, 51014 Tartu
  Fax:   (+372) 7 383 041 |               Estonia
  indrek@indr...        |         www.bps.co.ee


Hi Jay,

What is your reference for the ADC ?
Internal or Vcc ???
It you're using Vcc as a reference, then it could be that you have power
supply problem, and connecting the JTAG stablises Vcc better.
(assuming you have Vcc JTAG connected onto target Vcc)

If you're using internal Ref, then I'm out

-- Kris

> Hello Guys
> 
> I have a strange problem, I am logging pressure sensor data using 
> F1232 via its one of the ADC channel. When the pressure sensor is 
> stable, I get a 0.69V~0.71V (i.e. no presssure applied). This works 
> as expeced when debuggin in JTAG mode.
> 
> However when I run the same code standalone, the ADC reading for the 
> same case is fluctuatig (0.69V~0.80V). The only difference is that I 
> have detachted the JTAG cable, what could be wrong, where should I 
> start looking into? Any ideas?
> 
> Cheers
> Jay





Hi

It is powered by a Li-Poly battery, with bypass caps and a LP2980 
Voltage reg with an output of 3.3V.

I left the batt attached when in JTAG mode too, if it were noise, it 
should affect the JTAG session as well right?

Cheers
Jay

--- In msp430@msp4..., Indrek Rebane <indrek@b...> wrote:
> Hi Jay,
> 
> hc08jb8 wrote:
> > However when I run the same code standalone, the ADC reading for 
the
> >  same case is fluctuatig (0.69V~0.80V). The
only difference is 
that I
> >  have detachted the JTAG cable, what could be
wrong, where should 
I 
> > start looking into? Any ideas?
> 
> Noisy power supply, attach the scope.
> 
> Indrek
> 
> -- 
>   Indrek Rebane           |      Borthwick-Pignon
>   Electronics Engineer    |    Tartu Science Park
>   Phone: (+372) 7 302 641 | Riia 185, 51014 Tartu
>   Fax:   (+372) 7 383 041 |               Estonia
>   indrek@b...        |         www.bps.co.ee





Thanks guys, I think it is the noise problem, I tried some test of 
supplying a well regulated power bypassing the regulation circuitry 
and it seems to work fine. :-)

Now, the second question is what can I do to minimise or eliminate(?) 
this noise issue? Make a big cpper gound beneath? Any tips?

Thanks
Jay



--- In msp430@msp4..., "microbit" <microbit@c...> wrote:
> Hi Jay,
> 
> What is your reference for the ADC ?
> Internal or Vcc ???
> It you're using Vcc as a reference, then it could be that you have 
power
> supply problem, and connecting the JTAG stablises
Vcc better.
> (assuming you have Vcc JTAG connected onto target Vcc)
> 
> If you're using internal Ref, then I'm out
> 
> -- Kris
> 
> > Hello Guys
> > 
> > I have a strange problem, I am logging pressure sensor data using 
> > F1232 via its one of the ADC channel. When the pressure sensor is 
> > stable, I get a 0.69V~0.71V (i.e. no presssure applied). This 
works 
> > as expeced when debuggin in JTAG mode.
> > 
> > However when I run the same code standalone, the ADC reading for 
the 
> > same case is fluctuatig (0.69V~0.80V). The
only difference is 
that I 
> > have detachted the JTAG cable, what could be
wrong, where should 
I 
> > start looking into? Any ideas?
> > 
> > Cheers
> > Jay
> 
> 
> 




Hi again Jay,

hc08jb8 wrote:
> Now, the second question is what can I do to minimise or eliminate(?)
>  this noise issue? Make a big cpper gound beneath? Any tips?

Capacitance. Quantity is not as important as quality (location,
routing). There have been many books and papers written about the
subject. First two papers I suggest you to read are:

http://www.si-list.org/files/published/sun/cpmt_1999.pdf
http://www.si-list.org/files/published/sun/cpmt_2001.pdf

Also, search in SI-List archives would not hurt:
http://www.freelists.org/archives/si-list/

Indrek

-- 
  Indrek Rebane           |      Borthwick-Pignon
  Electronics Engineer    |    Tartu Science Park
  Phone: (+372) 7 302 641 | Riia 185, 51014 Tartu
  Fax:   (+372) 7 383 041 |               Estonia
  indrek@indr...        |         www.bps.co.ee


Filter the switcher a little better, did you use the basic circuit or 
did you calculate the ouput cap for very low jitter? Are you separating 
the Vcca and Vcc supplies? and separately filtering them? Are you doing 
the same for the Vssa and Vss lines. Have you correctly filtered Vref 
etc etc.

Al

hc08jb8 wrote:

> 
> 
> Thanks guys, I think it is the noise problem, I tried some test of 
> supplying a well regulated power bypassing the regulation circuitry 
> and it seems to work fine. :-)
> 
> Now, the second question is what can I do to minimise or eliminate(?) 
> this noise issue? Make a big cpper gound beneath? Any tips?
> 
> Thanks
> Jay
> 
> 
> 
> --- In msp430@msp4..., "microbit" <microbit@c...> wrote:
> 
>>Hi Jay,
>>
>>What is your reference for the ADC ?
>>Internal or Vcc ???
>>It you're using Vcc as a reference, then it could be that you have 
> 
> power
> 
>>supply problem, and connecting the JTAG stablises Vcc better.
>>(assuming you have Vcc JTAG connected onto target Vcc)
>>
>>If you're using internal Ref, then I'm out
>>
>>-- Kris
>>
>>
>>>Hello Guys
>>>
>>>I have a strange problem, I am logging pressure sensor data using 
>>>F1232 via its one of the ADC channel. When the pressure sensor is 
>>>stable, I get a 0.69V~0.71V (i.e. no presssure applied). This 
> 
> works 
> 
>>>as expeced when debuggin in JTAG mode.
>>>
>>>However when I run the same code standalone, the ADC reading for 
> 
> the 
> 
>>>same case is fluctuatig (0.69V~0.80V). The only difference is 
> 
> that I 
> 
>>>have detachted the JTAG cable, what could be wrong, where should 
> 
> I 
> 
>>>start looking into? Any ideas?
>>>
>>>Cheers
>>>Jay
>>
>>
>>
> 
> 
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