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CC2640: cJTAG needs to have Y1 (24MHz) or Y2 (32.768KHz) to be functional?

Part Number: CC2640
Other Parts Discussed in Thread: TIDA-00757

- I have sent the schematic to local FAE and he should have sent it to you.

- U2 (CC2640) is powered by +3V;  VDDR (pin 28 & pin 32) measures around 1.8V; DCOUPL (pin 12) measure about 1.3V; these voltages seem to be correct according to the datasheet.

- I measured Y1 (24MHz crystal) pin 1 or 3 but there is NO clock.  I assume there should be a clock if the CC2640 microprocessor is up and running.

- I connected to cJTAG using the SmartRF06 EVM but wasn’t able to detect the CC2640.  Does the cJTAG needs to have Y1 (24MHz) or Y2 (32.768KHz) to be functional?

- C10 & C11 for Y1 are NOT currently installed according to the reference design TIDA-00757 (Smart-Lock).  Y1 (TSX-3225 24.0000MF20G-AC3) datasheet calls out 9pF of loading capacitors.  Is there a reason why the reference design does not need them?

  • Hi Chao,

    Note that you should not probe directly on the 24 MHz crystal. This can cause permanent damage to the device (as stated in the datasheet).

    None of the crystals are required for JTAG to work.

    The 24 MHz crystal pins have internal load capacitor banks. The load capacitance can be adjusted up to 9 pF.

  • Hi Fredrik,

    Thank you for your quick reply and information.

    Where in the datasheet that says should not probe directly on the 24MHz crystal?  I'm not seeing it.  I wonder if I have the older datasheet.

    I'm trying to connect to the CC2640 via cJTAG using the SmartRF06 EVM but it didn't detect the CC2640 device.  Am I doing something wrong?



  • Hi Chao,

    This is stated in note 1 in the 24 MHz crystal oscillator section. Note that this is not a problem if you are not using the DCDC regulator.

    Are you sure all your JTAG signals are connected correctly? What do you mean by "not detected"? What do you see if you run Flash Programmer 2?

  • Hi Fredrik,

    Yes, I double checked all the cJTAG (not JTAG) signal connections and they are correct as recommended by the SmartRF06 User Guide Figure 24 (see attached file: cJTAG connections). 

    For cJTAG, I've connected the following signals:

    1) VDD_SENSE (3.3V from my board), JTAG_TMS, JTAG_TCK, RESET, and GND from SmartRF06 EB P410 (10-pin ARM Cortex Debug Header) to my board. 

    The jumper settings on SmartRF06 are:

    1) P408 - all jumpers are ON (connected)

    2) J503 - jumper on mounted (using VDD on my board)

    I made the cJTAG connection between SmartRF06 EB to my board via the 10-pin flat cable provided with the SmartRF06 EB (see attached file for connection diagram: cJTAG setup pic)

    I power the SmartRF06 first, then my board with the CC2640 device.

    I run/open the Flash Programmer 2 software.  It shows the XDS100v3 is detected.  Below XDS100v3 it shows Unknown device (see attached pic: FlashProgram2 Open).

    When I click on the "Unknown" icon below XDS100v3, it shows "selected device could not be indentified." 

    If everything is working properly, below XDS100v3 it should show the CC2640 device instead of "Unknown".

    Does XDS100v3 support cJTAG?  I am assuming it does because I'm following the exact directions from the TIDA-00757 users manual (TIDUBV3A) pages 36 to 37.  TIDA-00757 reference design uses the same device that I'm using, the CC2640.

    Please let me know if I am doing something incorrect.



  • Hi Fredrik,

    I was able to detect and connect to the CC2640 device on my board using Flash Programmer 2 now.  I am able to flash the device with .hex file!

    Thanks for your help.



  • Good to hear!

    Was it just because the debug cable was connected the wrong way on the SmartRF06EB?