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External flip-flop chip to synchronize an external asynchronous input

  1. Nov 12, 2006 #1
    Hello everyone,

    I am using an external flip-flop chip to synchronize an external asynchronous input into a microcontroller. So, what I am wondering about is how to provide a clock into the FF chip.... it has to run at the same rate as the system clock of the microcontroller. Is there a way to take the oscillator clock out on a pin? ... in general that is....
    I was also thinking of generating a wave from PWM with unscaled clock and rout it to the FF.... or would i have to have a separate crystal oscillator chip? The microcontroller is motorolla 68hc12.
    Thanks in advance.
  2. jcsd
  3. Nov 13, 2006 #2
    nevermind.... found something in the pile of documentation on the core where i can take the clock out on a pin...
  4. Nov 13, 2006 #3


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    Staff: Mentor

    Remember that it takes 2 FFs to synchronize the signal. Is the 2nd FF the input into the uC?
  5. Nov 13, 2006 #4
    :biggrin: :biggrin: yeah, berkeman... THAT i have learned on my own mistake and will not forget. For FFT project i am writting flip-flops in vhdl, no externals.

    But this one is a project on speed-detection using microcontroller, in which case i have to use external chips. Seems like it is possible to 'rout out' a clock from the core.
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