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c6748 RTC problem

si cheng
Expert 2685 points
Other Parts Discussed in Thread: OMAP-L138

hello:

I am now working with C6748, and I have an TI EVM , I want to use the RTC, then I write the RTC code ,and test on the TI EVM ,it work well,But

when I use the RTC code on my c6748 board , it can't work. I just modify the PLL, make sure my board CPU works on 300Mhz,the same with TI's EVM.

Because my  board is 12Mhz External crystal and the TI EVM is 24Mhz External crystal. I found that after  I wrote the RTC's kick registers, I can't not write any value

into the other RTC register, for example ,sencond, minute registers, and so on. I don't know why. Can anyone hlep me?

Thank you very much!

best~

  • 0
    TI__Expert 7470 points

    Hi,

    Which TI EVM are you using? Have you copied the TI EVM's RTC power/clock design in your board design? I assume you are providing the proper reference clocks to the RTC.

    Also remember that it takes 4 AUXCLK cycles (clock into RTC logic) for a write to the RTC registers to take effect. Since the AUXCLK on your board is 1/2 that of the TI EVM, you should double the wait loop after every write to any RTC register before reading it back.

    Regards,

    Sunil Kamath

  • 0 in reply to Sunil Kamath
    Expert 2685 points

    hello：

    My EVM is Zoom OMAP-L138 EVM Development kit. The clock reference for the RTC is an external 32.768-kHz crystal. The crystal is connected

    between pins RTC_XI and RTC_XO.Below is the RTC design. I have done what you suggested. But it don't work. Can you give me oher advice?

    Thanks

    . 

  • 0 in reply to si cheng
    TI__Expert 7470 points

    Hi,

    Do you wait for 4 AUXCLKs after writing to the RTC kick registers? Try increasing the wait time to a higher value just to rule out this issue. If this still does not work, please try the following:

    1) wait for 3 32KHz clock cycles after resetting the RTC before writing to any of its registers, or

    2) it may be that the crystal is not able to sufficiently drive the oscillator. The resistor between XI and XO is not required for the C6748 as this has been designed into the device - try removing R110 from your board.

    I am assuming that RTC power is being correctly provided.

    Regards,

    Sunil Kamath

  • 0 in reply to Sunil Kamath
    Expert 2685 points

    Hi，

    I solve the problem ,it's external battery problem, the external battery is dead, and I chage another battery, the the RTC is OK.

    Thanks!