How to detect if VBAT supply is present for RTC to work?

[Amit_Kumar1]

Hi

I am using K60 custom made board with cw10.6. In my application I have to time stamp the data. for that I am using RTC. If VBAT pin is given a supply of 3.6V through a coin cell and then the program is dumped, my code is works fine . Suppose my battery is dead, my programs hangs and keeps restarting. Is there any way to find out if VBAT supply is present?

During Initialization I want to check if VBAT supply is present only then I will initiate the RTC else I will use some other clk source i.e from different uc. I also wanted to know what will happen if  VBAT pin is left open? Will my entire program hang or will the rest of the program work excluding RTC?  I will be using PE component for RTC.

Kind Regards

Amit Kumar

[Paul_Tian]

Hi, Amit

Do you use external 32.768KHz for RTC module? If yes, you can check 32.768KHz has been setup? If setup is OK, battery is no problem.

Best Regards

Paul

[Amit_Kumar1]

Hi Zhe

Thanks for the quick reply. I am using external 32.768KHz for RTC module. My program was working fine until I took out the coin cell, i did POR but still the issue was there. even after inserting it back and doing POR the issue still persist.

Kind Regards

Amit Kumar

[egoodii]

What you've got DIRECTLY to work with is TIF (Time Invalid Flag) in RTC_SR as set by VBAT_POR, and procedures must ensue to restart the RTC when this gets set (including long oscillator startup, if used).

You should also be aware of dV/dT limitations in the chip relative to instantaneous battery-connect, especially in early silicon.

[Amit_Kumar1]

Hi Earl

I tried reading all the registers. If the VBAT is connected to 3.3 v source, it gives the o/p. In case if it is floating then my program enters in hard fault. I am using the following code

/*lint -save -e970 Disable MISRA rule (6.3) checking. */

int main(void)

/*lint -restore Enable MISRA rule (6.3) checking. */

{

/* Write your local variable definition here */

/*** Processor Expert internal initialization. DON'T REMOVE THIS CODE!!! ***/

PE_low_level_init();

/*** End of Processor Expert internal initialization. ***/

printf("testing starts\n");

/* Write your code here */

for(;;)

{

printf("%0X,%0X,%0X,%0X,%0X,%0X,%0X,%0X,%0X,%0X\n",RTC_TSR, RTC_TPR, RTC_TAR, RTC_TCR,RTC_CR, RTC_SR, RTC_LR,RTC_IER, RTC_WAR,RTC_RAR);

WAIT1_Waitms(2000);

}

the same code works if the VBAT is connected 3.3V.

Kind Regards

Amit Kumar

[egoodii]

I am not surprised that the RTC subsystem must be powered-up to access the registers.  The 'normal connection' is a BAT54C to VDD and coin-cell, thence 100ohms surge-limiter to the VBAT pin.  If, when you power it up 'so connected' but if no/invalid coin-cell voltage came 'previously' you should get the VBAT_POR (Power On Reset) indication.

[Amit_Kumar1]

HI Earl

Thanks for the schematic. I went through the schematic of the TWR board which had this type of setup. I wanted complete isolated setup for the RTC.

In the reference manual I found hat some access control register is there which can be read. I wanted to know where is that?

Kind Regards

Amit Kumar

[Jorge_Gonzalez]

Hello Amit:

Just in case you did not find the answer to your last question:

Access control registers refers to RTC_RAR and RTC_WAR registers. As you can read in the manual, these registers are not powered by VBAT:

Regards!

Jorge Gonzalez

[Amit_Kumar1]

Hi Jorge

Thanks for your valuable reply. I tried reading all the register one at a time. In that process I tried reading the above 2 registers which you mentioned. But when Vbat is not powered, The program hangs at the reading statement. If VBAT is powered then I am able to read all the registers. But this won't solve my issue.

Kind Regards

Amit Kumar