Tool/software:
Hello
I want to make a circuit to monitor the status of reset signal of the Micro.
The reset signal is a low level 20us signal.
If I receive 3 pulse in 10ms, I would like to output a pulse. And I would like to bypass the first pulse.
Do you have an idea of this kind of circuit?
Thanks!
The three flip-flops form a shift register. On each falling edge of the input signal, a '1' is shifted through; at the third falling edge, the output of the final flip-flop goes high and triggers the multivibrator, which outputs a 20 µs pulse. This pulse is also used to clear the flip-flops so that counting begins again at 0.
The multivibrator at the top implements the timeout. For 100 ms after each rising edge of the input signal, its output is high, and the two AND gates allow the '1' bit to be shifted through. After 100 ms, the last two flip-flops always see a '0' at their input.
The /RESET signal is needed to initialize the flip-flops to a known state at power up. Generate it with a reset IC like the TLV809E or (if you know the rise time of the supply) with an R-C circuit.
multivibrators: SN74AHC123A/TPUL2G123, or any '123
flip-flops: SN74HC175, or any '174/'175
NOT gates: SN74LVC2G14, or any '04/'14
AND gates: SN74HCS08, or any '08
