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Regarding Vbat pin connection with TM4C1294NCPDT

Rahul Kumar38
Prodigy 250 points
Other Parts Discussed in Thread: EK-TM4C1294XL

Hi,

i am using CR2032 Cmos battery for powering up internal RTC Must be in Running.

But i am not able to find which pin to be connected on Tiva Board,As i hav eseen so many post it states that pin 68 of launch pad is connected to Vbat.

But can any one tell me which pin no is availabale is on Tiva TMC1294NCPDT and what are the codes which are available used for configuring the hibernate.

By this requirement I have to make the RTC keep running when power suplly from USB is offf?

Is it posiible or if not can anyone help me out?

  • 0
    Prodigy 210 points

    If the "Tiva Board" you're referring to is the EK-TM4C1294XL LaunchPad, then Vbat is not broken out to any of the pin headers, nor is there a battery holder on the board. This is too bad, and very common--I suppose vendors do this to save money on their cheap and cheerful loss-leader boards like the LaunchPad.

    According to the board's schematic, Vbat is connected directly to 3.3v via R38. You could remove R38 and connect a battery to the R38 pad that goes to Vbat on the MCU.

  • 0 in reply to Jerry Gardner
    Prodigy 250 points
    thanks Jerry

    But i could not find that Vbat pin.
    i have battry can i connect that battry (+) to pin 3.3V on Tiva launch pad and (-)negative to ground. so that Vbat can able to Drive RTC? is it possible?

    I have one more issue i have to make the tiva board to sleep permanentley and it shd get wake up when ever their is an interrupt acuurs from UART.
    Kindly anyone suggest me some code??
  • 0 in reply to Rahul Kumar38
    Prodigy 210 points

    Vbat is pin 68 on the TM4C129. It's connected to 3.3v through R38. Connecting the battery to the board's 3.3v pin won't do you any good. You need to isolate Vbat by removing R38 and connecting the battery to the R38 pad that goes to pin 68 on the micro.

  • 0 in reply to Jerry Gardner
    TI__Guru**** 244400 points
    Hello Jerry,

    It must be R39 and not R38 resistor that needs to be removed. Removing the R38 will still keep the WAKE pin connected to the Main MCU power supply. So in VDD3OFF mode, this will cause the WAKE pin to go low due to voltage decay and wake up the device.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Prodigy 210 points
    If the WAKE* input is active when Vdd goes away and the MCU is running from Vbat, then yes, you need to make sure that WAKE* is pulled high. Removing R39 makes connecting a battery even easier because you can solder the + lead from the battery to TP11, which is easier than soldering it to the pad of a small surface mount resistor.
  • 0 in reply to Jerry Gardner
    Prodigy 250 points

    Thanks.

    But can u please guide me some code which is based on interrupt based  and it should function whenever UART comes in picture??

    So whenever their is data on UART pin the tiva must get awake from sleep mode and it must response to received data and later again  tiva must go in sleep...

    Please

    Any one guide me..

  • 0 in reply to Rahul Kumar38
    TI__Guru**** 244400 points
    Hello Rahul,

    Sleep and Hibernate Mode are different

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Prodigy 250 points
    ok thanks AMIT
    i have connected 3V battry to "JP2 pin" which gives 2.72V across TP11 and 2.5V across R38 (acoording to schematic) .Is this proper for driving RTC when it enters in sleep mode if YES ?can u give more details about code.....

    I have one more issue i have to make the tiva board to sleep permanentley and it shd get wake up when ever their is an interrupt acuurs from UART.
    Kindly anyone suggest me some code??
  • 0 in reply to Rahul Kumar38
    TI__Guru**** 244400 points
    Hello Rahul,

    JP2 is not the correct place for the battery. It is supplying all the supply rails and causing current drain. The battery will not last long enough.

    Regards
    Amit