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24Mhz Crystal is not working with 32 Khz Crystal

Brajesh Sharma
Expert 1785 points

Other Parts Discussed in Thread: CC2640

Hi ,

I'm having certain queries regarding Clock settings of CC2640. In our custom board, we have two Crystals for clock, 24Mhz & 32kHz Crystals. I'm using TI's SimpleBLEPeripheral Example and after probing i notice, only 32kHz crystal is providing clock which is optional Crystal and there is no clock @ 24Mhz. 

As per working wise, I don see any issue with only 32Khz Clock but since that is slow clock also a Optional, i am not sure whether it's okay to go ahead with. 

Also when we remove 32kHz Crystal, FW automatically switches to 24Mhz crystal and works okay till connection. With 24Mhz Clock, device gets disconnected within 15 seconds of connection, every time.

Any suggestion would be well appreciated.

Thanks

Brajesh

  • 0
    TI__Guru 57545 points
    Hi,

    Probing directly on 24MHz while the DCDC vonverter is enable might cause permanent damage to the device, which is stated in datasheet section 5.10 note (1).

    Since it's custom board, did you follow our reference design?
    processors.wiki.ti.com/.../CC26xx_HW_Checklist
    you can find more information here :

    processors.wiki.ti.com/.../Category:BluetoothLE
  • 0 in reply to Christin Lee
    Expert 1785 points
    Hi Christin,

    Thanks for the reply, I understand the fact that it can damage the device, but I need to confirm the whether that crystal has actually been used or not. I know advertising and connection suggests that 24MhZ crystal has been used , but isn't there any way that we can actually probe or see the clock. ?

    Thanks
    Brajesh
  • 0 in reply to Brajesh Sharma
    TI__Guru 57545 points
    You can probe it once you disable DCDC. In order to do that, you need to modify it in ccfg.c
    The FW won't switch your sclk_lf source unless you modify the ccfg setting and also we don't support sclk_lf source to be 24MHz crystal.
    Please take a look at our software developer's guide section 3.10.5
    For disabling DCDC,
    #define SET_CCFG_MODE_CONF_DCDC_RECHARGE 0x1 // Do not use the DC/DC during recharge in powerdown
    #define SET_CCFG_MODE_CONF_DCDC_ACTIVE 0x1 // Do not use the DC/DC during active mode

    For changing sclk_lf source

    #define SET_CCFG_MODE_CONF_SCLK_LF_OPTION 0x2 // LF XOSC
    or
    #define SET_CCFG_MODE_CONF_SCLK_LF_OPTION 0x3 // LF RCOSC

    Also you can route out your 32kHz signal to GPIO by doing the following, so that you don't need to probe the 32kHz crystal.

    IOCPortConfigureSet(IOIDn, IOC_PORT_AON_CLK32K, IOC_STD_OUTPUT);
    AONIOC32kHzOutputEnable();

    What was the intention for checking xtal frequency?