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TMS320F28335: Switching from crystal to external oscillator

Christopher Mounce
Prodigy 160 points
Part Number: TMS320F28335


On an F28335 design, I'm trying to switch from a 30 Mhz crystal using X1/X2 to using only a 30 Mhz external oscillator on the XCLKIN pin, with X1 grounded and X2 unconnected. What, if any, changes are required in code to shift from using the crystal to using the oscillator? Since it's the same PLL multiplication, I figured it would be the same, but I am unsure, and I see nothing in the documentation about a difference in register setup requirements for one configuration vs the other.

  • +1
    TI__Guru* 81560 points

    Christopher,

    Thanks for reaching out, in this design the inputs from the X1 pin and the XCLKIN are XOR'd before they propagate to the PLL(or bypass mux).  So, as long as you are grounding the X1 on the revised schematic you are good to go.  I've included the clock diagram from the TRM for reference.

    Best,

    Matthew