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TM4C123GH6PM: Does TM4C123G support 19.2 MHz quartz?

Pavel Mychko
Intellectual 360 points
Part Number: TM4C123GH6PM

I found out that TM4C123G microcontroller uses direct quartz frequency to speed up its PLL. So there is a list of supported quartzs. But I can't found in this list 19.2 MHz - one of the most common quartzs ever. How it's possible?

  • 0
    TI__Guru 72500 points

    The frequency range of crystals supported is 4MHz to 25MHz. 19.2MHz will work, but not for USB. There are details about selecting the crystal in section 24.9.5 of the datasheet. Check the footnotes of table 24-18. 

    https://www.ti.com/lit/ds/symlink/tm4c123gh6pm.pdf

  • 0 in reply to Bob Crosby
    Intellectual 360 points

    Sorry, I still can't find something about that crystal in the datasheet. Of course it works as it (this crystal set up on my board right now) but I was forced to do some tricks with dividers to adjust frequencys. I'm talking about the "native" support - it would be great to add it into processor and datasheet.

  • 0 in reply to Pavel Mychko
    TI__Guru 72500 points

    You are correct, there is no 19.2 MHz crystal in that table. I was referring to the information about selecting a crystal that is not in the table. If you are only making a few devices saying " Of course it works as it (this crystal set up on my board right now)" might be sufficient. However, if you are going to produce a product in volume you should take the time to look at the crystal ESR and select the proper tank circuit (capacitors and resistor). Also, I highly recommend having your design characterized by the crystal manufacturer before going into volume production.

    While 19.2 MHz used to be a popular crystal choice, we have had no other requests for using that crystal value in the last seven years. The use of higher frequency PLLs and fractional dividers for UART baud rate generators has reduced that requirement. We currently have no plans to update the datasheets with a 19.2MHz crystal in the table. However, we will keep your suggestion in mind for the future.

  • 0 in reply to Bob Crosby
    Intellectual 360 points

    Thank you for the clarification. I hope if there is a new chip revision, this crystal will appear.