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reset and startup problem with stand alone msp430g2553 board

davide pasini
Prodigy 80 points
Other Parts Discussed in Thread: MSP430G2553, ENERGIA

Hi,

After some months of launchpad experiences I'm developing my first stand alone board.

 

On the board there are these smd components for now.

MSP430G2553 Tsop28pins

Voltage regulator at 3,3V

Anaren RF module.

A led with 150ohm resistor.

 

I think I've a problem with the sturtup and reset.

There are 2 decoupling ceramics capacitors for the voltage regulator (about 4,7uF)

There is a 100nF capacitor connected ad VCC and GND 10mm far from the microcontroller.

There is a 47K resistor between Vcc and the RESET pin.

 

 

Often if I connect the battery (nominal 3.7V) the circuit works well but it is not stable.

Often it doesn't start.

 

Sometimes when it doesn't work there is a 1V across the 47K resistor. If I decrease the resistor value it works better but there are the same problems.

 

 

I tried to remove the RF module and write a simple led blink program (I use Energia IDE) but the problems are the same.

 

Thank you for your help.

 

ilpaso

 

  • 0
    Guru 46710 points

    davide pasini said:
    There is a 47K resistor between Vcc and the RESET pin.

    Reset pin circuit includes capacitor. Do you have any? If not - then most probably this is your problem.

  • 0
    Guru 227245 points

    davide pasini said:
    Sometimes when it doesn't work there is a 1V across the 47K resistor.

    Weird. This means 21µA input current into the RST pin. Which shouldn't happen. Anything else connected to the pin? FET?

    maybe the VCC pin isn't soldered correctly and some power is drawn through the reset pin and the clamp diodes?

  • 0 in reply to Jens-Michael Gross
    Guru 46710 points

    Jens-Michael Gross said:
    Sometimes when it doesn't work there is a 1V across the 47K resistor.

    Weird. This means 21µA input current into the RST pin. Which shouldn't happen.[/quote]

    Why you say so? If reset is not done properly and microcontroller is in "limbo" - virtually anything can happen including some latch-up of reset pin internal circuit. My guess here is that by adding capacitor to reset pin all the problems will go away including particular one.

  • 0 in reply to Ilmars
    Prodigy 80 points

    Hi everyone,

    There was a 1nF capacitor at the RST pin but the problems were the same.

    No other components are connected to the RST pin. I've removed the voltage regulator too but nothing changed.

    I've soldered 2 boards with the same problem.

    Is important the width and the length of the reset trace?

    bye

    ilpaso

  • 0 in reply to davide pasini
    Guru 46710 points

    davide pasini said:
    There was a 1nF capacitor at the RST pin but the problems were the same.

    You shall program chip and then do testing using big enough capacitor here, like 100nF.

    Side question: do you happen to change DCO frequency in your firmware?

  • 0 in reply to Ilmars
    Prodigy 80 points

    Ilmars said:

    You shall program chip and then do testing using big enough capacitor here, like 100nF.

    Side question: do you happen to change DCO frequency in your firmware?

    I'll try with a bigger capacitor.
    No changes to DCO frequency.
  • 0
    Expert 1620 points

    If you're not using the 32kHz crystal then you need to clear the oscillator fault flag and take it out of crystal mode like so:

    IFG1 &= ~OFIFG;
      while (BCSCTL3 & LFXT1OF)
          BCSCTL3 = LFXT1S_2;

    I do it right after

    WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT

  • 0 in reply to Ilmars
    Guru 227245 points

    Ilmars said:
    Why you say so? If reset is not done properly and microcontroller is in "limbo" - virtually anything can happen including some latch-up of reset pin internal circuit.

    How that? The reset pin is a plain CMOS input. And therefore shouldn't have more than 50nA input leakage unless the voltage on RST is >Vcc.

    Ilmars said:
    My guess here is that by adding capacitor to reset pin all the problems will go away including particular one.

    Possible. Still doesn't explain why there is such a high input current into RST - unless RST is connected with the FET and current flows there.

  • 0 in reply to Jens-Michael Gross
    Guru 46710 points

    Jens-Michael Gross said:
    The reset pin is a plain CMOS input.

    If it is plain CMOS input - then yes. But is it? To avoid any assumptions - do you know any document with actual reset (pin) internal circuit of msp430g2553 shown?

  • 0 in reply to Ilmars
    Guru 227245 points

    Ilmars said:
    If it is plain CMOS input - then yes. But is it? To avoid any assumptions - do you know any document with actual reset (pin) internal circuit of msp430g2553 shown?

    Since it is no GPIO port pin, it is not listed in the port pin schematics section. But the RST pin is listed in the chapter for the GPIO electrical specs as a footnote, along with the XTIN pins in bypass mode. At least in some datasheets.

    But you're right, it's only an assumption. But based on valid reasoning.

  • 0 in reply to Jens-Michael Gross
    Expert 2555 points

    For anyone happening on this thread in the future... I had a similar problem, adding a cap on reset pin seems to resolve the issue.

  • 0 in reply to Martin Helie
    Guru 74080 points
    The combination of a resistor to Vcc AND a capacitor to GND is recommended by the manufacturer. Even the values are given. I wonder why one should use it in a different way to later figure out it works better when following the recommendation.

    Dennis
  • 0 in reply to Dennis Eichmann
    Expert 2555 points

    I should have been more specific. The 1n cap (maybe because the ones I am using are out of spec) don't always cut it. Using a higher value cap works best.

  • 0 in reply to Martin Helie
    Guru 227245 points
    The really required capacitance depends on the power supply. If you hav a power supply that provides an instantaneous rise form 0 to VCC, you don't need a cap at all. But only a battery pack is that fast.

    The slower voltage rises, the higher the cap should be.
    Ony my own hardware, I used 100nF/10K. But with introduction of SBW, the maximum cap is limited to 2nF. And a 500M pull-up doesn't sound a good idea.
    A possible way is to use connect a 100nF/10K combo through a 1k series resistor to the RST pin. So for SBW, the cap is separated from RST with 1k. Which prevents the SBW signals to be shorted to GND by the cap while still keeping RST low on power-on while VCC is still rising.
  • 0 in reply to Jens-Michael Gross
    Prodigy 160 points

    Hey Jens-Michael,

    I have exactly the same problem and the same current measurement for two of my self made board with the same 28 pin chip. 47k pull up and 2.2nF capacitor. no other connections to the reset pin. input voltage is 3.3V and the VCC pin for the microcontroller is decoupled with 100nF and 10uF. Any idea what is really going on? For my first board I thought it might be ESD damage during my handling, but when it happens to my second board, there for sure should be something wrong, running out of ideas. Any suggestions will be helpful. Thanks very much.

    Joe

  • 0 in reply to Liqiang Du
    Guru 46710 points
    >I have exactly the same problem and the same current measurement for two of my self made board with the same 28 pin chip. 47k pull up and 2.2nF capacitor.
    First you shall try 100nF/47k+1k_series to see if it helps. If not - then your problem could be elsewere.
  • 0 in reply to Liqiang Du
    Guru 227245 points
    YOu don't write which MSP you use. Most of the 5x family or newer MSPs have an internal pull-up on RST (40-60k). (on the 5438 and some others it isn't enabled on power-up, making it useless)
    In these cases, the external resistor is not only superfluous, it effectively halves the pulldown capacitance. Take a look at your VCC with a scope. How long does it take to settle?
    With the internal resistor, the 47k/100n/1k construct won't work effectively anymore. But you can simply try 1k/100nF in series from RST to GND.

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