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TCAN4550: How much communication without 40MHz crystal

Ole Kristian Western
Prodigy 85 points

Part Number: TCAN4550

Hello,

I am developing a driver for the si4455. We have a custom board, and due to unforeseen issues the shipment with crystals is delayed.

I can read out the registers to get the chip id and so on (16'h0000 to 16'h002F), but which other registers should I be able to read without crystal?

As I understand it, registers in the SPI CLK domain is not dependent on the crystal and can be read without the crystal in place. Also, what other operations can we do without the crystal?

I've read the chip is sensitive to crystal, matching and biasing. So it would be good to know which registers I should be able to read, to distinguish between crystal and software/spi communication problems.

  • +1
    TI__Guru 74372 points

    Ole,

    Only the registers starting with 16'h00 can be read without the crystal. All registers with 16'h08xx and 16'1xxx require a crystal for operation, and these are all the registers that control and configure the CAN communication on the device. So, he device really isn't usable without the crystal unfortunately. It does accept a single-ended input clock though, so is it possible to develop using that method until the crystals arrive?

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 85 points

    Thanks for your answer. Yes, I suspected that. I've tried to inject a 40MHz (1Vp-p) sine into OSC1 (and ground of the function generator to GND of the chip). I'm not sure if this is correct voltage?

  • 0 in reply to Ole Kristian Western
    TI__Guru 74372 points

    Ole,

    The logic high and low levels on OSC1 are based on the VIO pin voltage. a high level is 0.85*VIO to 1.1*VIO and a low level is anything under 0.3*VIO.

    Regards,

    Eric Hackett