External flip-flop chip to synchronize an external asynchronous input

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Discussion Overview

The discussion revolves around the use of an external flip-flop chip to synchronize an external asynchronous input to a microcontroller, specifically the Motorola 68HC12. Participants explore methods for providing a clock signal to the flip-flop chip, considering various approaches and implications for their project on speed detection.

Discussion Character

  • Technical explanation, Experimental/applied, Conceptual clarification

Main Points Raised

  • One participant inquires about how to provide a clock to the flip-flop chip, questioning whether it can be extracted from the microcontroller's oscillator clock or if a separate crystal oscillator is necessary.
  • A later post indicates that the participant found documentation allowing them to extract the clock signal from a pin on the microcontroller.
  • Another participant reminds that two flip-flops are required to properly synchronize the signal, asking if the second flip-flop is the input to the microcontroller.
  • A subsequent response acknowledges the importance of using two flip-flops based on personal experience, while noting that their current project requires the use of external chips.
  • The participant mentions that routing out a clock from the core seems feasible for their application.

Areas of Agreement / Disagreement

Participants generally agree on the necessity of using two flip-flops for synchronization, but there is no consensus on the best method for providing the clock signal to the flip-flop chip, as different approaches are being considered.

Contextual Notes

There are limitations regarding the assumptions about the clock signal extraction and the specific requirements of the project, which may depend on the microcontroller's capabilities and the external flip-flop chip specifications.

Who May Find This Useful

Individuals working on microcontroller projects involving asynchronous signal synchronization, particularly those using the Motorola 68HC12 or similar architectures.

EvLer
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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.
 
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nevermind... found something in the pile of documentation on the core where i can take the clock out on a pin...
 
Remember that it takes 2 FFs to synchronize the signal. Is the 2nd FF the input into the uC?
 
berkeman said:
Remember that it takes 2 FFs to synchronize the signal. Is the 2nd FF the input into the uC?

: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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