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How does the 74HC245 on Altera DE2-115 board debounce the push buttons?

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matrixofdynamism

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The 74HC245 is given as "Octal bus tranceiver; 3-state". I am not sure what applications such a device is supposed to have. In any case, on the DE2-115 board, this chip is being used for purpos of debouncing the push buttons. How does it achieve that? Is it not true that a debounce circuit that reads the key input after a delay of first detecting a key down event, is sufficient for "debouncing the push button"?
 

It's a bit difficult to guess how this part is being used on this circuit without seeing the schematic, but there may be some plausible reasons, varying from: Just to protect the main chip against static voltages from finger; Allow separate general purpose 5v from core 3,3v, etc...
 

The "debouncing" is done by a 1 uF capacitor in parallel with each push button. The push button temporarily shorts the capacitor.
There is a 100k pull-up resistor for each button/capacitor. In this circuit the 74HC245 only a buffer/amplifier.
 

It's an example of a bad hardware debouncing circuit. A 1 µF shouldn't be discharged by a push-button without a small series resistor. And the slow rising edge is still at risk to be received as multiple edges if not processed by an ST gate. Using pure software debounce is probably more reliable.
 

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