CC2640R2F: Simple_peripheral in custom board application is not connecting with central with external crystal

Krishna priya Boban

Part Number: CC2640R2F
Other Parts Discussed in Thread: CC2640

I am trying to work with Simple_peripheral in custom board with external crystal (XCOSC_LF) enabled. I am using the same crystal as in CC2640 LAUNCHPAD , the project is working perfectly with launchpad . Also the project is working fine with RCOSC_LF in custom board.

But with the XCOSC_LF in custom board , it is advertising but when Im trying to connect it is immediately disconnecting with GATT CONN ERROR in NRF application. May I know possible reasons?

Note: When I took out the crystal output , it was around 31.26KHz instead of 32.76KHz . Can this be an issue?

over 3 years ago

0 Guillaume over 3 years ago

TI__Expert 5150 points

Hi Krishna,

It's definitely to be a crystal issue.

If you look at the data sheet product here :

https://www.ti.com/lit/ds/symlink/cc2640r2f.pdf

You can find at the §8.15 that the crystal should be 32.768kHz or around.

Regards,

0 Krishna priya Boban over 3 years ago in reply to Guillaume

Prodigy 220 points

Can this be a crystal calibration issue? I tried with two different crystals , and the crystal output is same 31.2khz .

0 Guillaume over 3 years ago in reply to Krishna priya Boban

TI__Expert 5150 points

It could be.

I will move the thread to the right expert thus you will have some more detailed clues for this issue.

regards,

0 desouza over 3 years ago in reply to Guillaume

TI__Guru**** 171649 points

Hi,

Measuring the LFOSC can easily skew its frequency and stability due to the capacitance of oscilloscope or DMM probes.

In this case, I strongly recommend following the measurement recommendations (section 5) and load capacitance (section 3.3) of the app note SWRA495 at: https://www.ti.com/lit/an/swra495i/swra495i.pdf

Hope this helps,

Rafael

0 Krishna priya Boban over 3 years ago in reply to desouza

Prodigy 220 points

Thank you for the reply

The measurement recommendations shown in section 5 is for High frequency crystal (XOSC_HF) right? Also, In that case, Would I be getting a precise 32.76 KHz with the same procedure in launchpad.

I will consider tuning the Load capacitance and will let you know. Meanwhile, I am open to take the suggestions.

0 desouza over 3 years ago in reply to Krishna priya Boban

TI__Guru**** 171649 points

Krishna,

Please apologize; indeed I got confused. However, even the 32kHz crystal is highly susceptible to direct measurement using a probe.

A very low input capacitance probe (an oscilloscope active probe, for example) can yield better results.

Apart from the crystal and any possible hardware problems, would it be possible to run a "known good" SDK example code in your board to see if the issue might be rooted in SW? Conversely, if your code can be run in a Launchpad, that could also help uncover a possible root cause.

Hope this helps,

Rafael

+1 Krishna priya Boban over 3 years ago in reply to desouza

Prodigy 220 points

Hi,

Thank you for the valued suggestion. The issue was with the Load capacitance itself. Now the crystal is giving required output. Even though it still need some stabilization , I understood where the problem lied.

Regards

Krishna priya

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CC2640R2F: Simple_peripheral in custom board application is not connecting with central with external crystal