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CC2541 Wake-up on Chip Select (SS)

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Expert 1570 points
Other Parts Discussed in Thread: CC2541

I'm using CC2541 in network processor mode connected via SPI to an application processor.  I have enabled POWER_SAVING and I'm following the protocol described in the source code: enable chip select, send a dummy byte (is this even required), disable chip select, wait until the device ready is asserted, then enable chip select and send my message.  Currently with BLE-1.3.1 release I'm seeing a 700us delay between when the master asserts the wake-up signal and when the slave asserts the data ready signal.

Is this delay something that is intrinsic to the processing capabilities of the CC2541, is it limited by the available clocks (I read somewhere that the 32kHz oscillator needs 400us to get ready), or what else?

Is it possible, by employing additional external clocks or other circuitry to drive that wake-up time down?

  • 0
    TI__Genius 12545 points

    Yes. It is a function of the 32kHz clock. The crystal oscialltor has very little drive, hence it take the clock time to establish itself.

    Using an external 32kHz clock might allow you to futher reduce this time.

  • 0 in reply to Chatto
    Expert 1180 points

    Is this the only prescribed way for waking up the device by using CS? That you have to lower CS, which wakes up the device and send the dummy byte. Raise CS again, wait for the given time for the CC2541 to wake up (700us), and then the CS can go low again and message can be read.

    Or, is there a way to just have a delay between the first time CS goes low and when data gets sent across the line that the device can be woken up, and the data can be read?