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TI MSP430 LED1 port alternating when I switch it on

Murat Aksoy
Prodigy 50 points

Hi,

I was working on the launchpad and decided to power the chip without it and wrote a simple program on IAR. 

All I do is stop the watchdog timer and turn on the LED1 port and then an infinite loop (tried asm and C). When I power the chip on launchpad either with usb or external power the LED1 port voltage is VCC. When I take the chip off and put it on the breadboard and power it up it's VCC/2. After checking on the oscilloscope I realized that it's (P1.0) alternating. Tried both on G2231 and G2211.

Thanks for the help guys.

  • 0
    TI__Guru**** 223157 points
    Hello Murat,

    When moved over to the breadboard, did you still have 10 uF and .1 uF capacitors connected from Vcc to GND? Is the RST line floating or do you have the 2.2 nF pulldown cap to ground and 47 kOhm pullup resistor to Vcc? It's possible that without these basic passive components you are constantly resetting the MSP430 to create the square wave seen.

    Regards,
    Ryan
  • 0 in reply to Ryan Brown1
    Prodigy 50 points

    Yes I do have a 10 uF and .4 uF tantalum capacitor connected from Vcc to GND. I forgot to actually look at the RST line and it's floating. I thought that was for the launchpad when it was connected via USB. Thanks for the heads up. "The power supply and the Spy-Bi-Wire JTAG signals TEST and RST must be connected with jumper J3 to allow the onboard emulation connection to the device." I thought it could float when not doing the onboard emulation.
    Murat

  • 0 in reply to Murat Aksoy
    TI__Guru**** 223157 points
    The RST line must be pulled up to Vcc in order for the device to run properly. Grounding the pin puts the device into a state of reset, and when left floating you can definitely expect the RST line to cause unwarranted resets.

    Ryan
  • 0 in reply to Ryan Brown1
    Prodigy 50 points
    Thanks for the answer. Can you delete this thread because it's embarrassing to make such a basic mistake :).

    Murat
  • 0 in reply to Murat Aksoy
    TI__Guru**** 223157 points
    Haha I wouldn't stress over it too much, basic mistakes happen all of the time. We're all humen ;) the whole point of this forum is for people to find answers to anything MSP430-related, if you had this question then someone else will have the same problem in the future and this thread could help them solve their issue faster!

    Ryan

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