External flip-flop chip to synchronize an external asynchronous input

AI Thread Summary
An external flip-flop chip is being used to synchronize an asynchronous input with a Motorola 68HC12 microcontroller. The user inquires about providing a clock signal to the flip-flop, considering options like taking the oscillator clock from a pin or generating a PWM wave. They discover documentation indicating that the microcontroller can output a clock signal. The discussion emphasizes the necessity of using two flip-flops for proper signal synchronization, with the second flip-flop serving as the input to the microcontroller. The project focuses on speed detection, necessitating the use of external chips for accurate operation.
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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