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TM4C123GH6PM: Using external VCXO or TCXO instead of the 16mhz crystal

can altineller
Expert 1720 points
Part Number: TM4C123GH6PM

Hello,

I would like to use a 16mhz vcxo module with my custom made tm4c123 board.

Currently I have a 16mhz 50ppm abracon oscillator that is depicted below:

VCXO's or TCXO's have LVDS versions which give out compementary outputs like:

How would I go about connecting an external oscillator to tm4c123gh6pm.

Best regards,

C.A.

  • 0
    TI__Guru*** 135355 points

    Hello C.A.

    Please review Section 3.7 of our System Design Guidelines for details about connecting crystal oscillators to TM4C123x MCUs: https://www.ti.com/lit/pdf/spma059

    Best Regards,

    Ralph Jacobi

  • 0 in reply to Ralph Jacobi
    Expert 1720 points

    Hello Ralph,

    I have reviewed both System Design Guidelines and the Datasheet, these are about connecting crystals, with the mcu, they form a crystal oscillator.

    But how about connecting an external generator that gives pulses, or differential pulses?

    Best Regards,

    C.

  • +1 in reply to can altineller
    Guru 92251 points
    can altineller said:
    But how about connecting an external generator that gives pulses, or differential pulses?

    The TM4C123GH6PM datasheet shows a single ended oscillator should be connected to the OSC0 input. Section 1.3.4.2 System Control and Clocks has:

    Main Oscillator (MOSC): A frequency-accurate clock source by one of two means: an external single-ended clock source is connected to the OSC0 input pin, or an external crystal is connected across the OSC0 input and OSC1 output pins.

    Table 24-18. Main Oscillator Input Characteristics has the following about the single-ended clock source:

  • 0 in reply to can altineller
    TI__Guru*** 135355 points

    Hello C.A.

    As Chester indicated, that is possible. System Design Guidelines also notes this:

    It is possible to use a single-ended clock source such as an external oscillator to drive the OSC0 input of the Main Oscillator Circuit. Refer to the device's data sheet for input specifications. When a single-ended clock source is used, the OSC1 pin should be left unconnected and GNDX2, if present, should be connected to GND.

    Best Regards,

    Ralph Jacobi