Outputs of Clocked Devices
How do I guarantee that the first output of a register or flip-flop will be valid?
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What we get fairly often on flip-flops is what is the state of Q after VCC is first turned on? That's once VCC has reached its recommended operating condition, what's Q? And the correct answer is that we don't know. And you won't know until a clockedge has come through.
So one solution to find out Q is this force a clockedge through when you know D is and then Q will be known. Another solution is to use a flip-flop that has clear and pre-set inputs, and then you can tie one of those inputs through a pull-down resistor to ground. And it'll force the output to that state. In clear, this is going to be putting out a low state. And the control line can force this high to start using the flip-flop.
This video is part of a series
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Logic and voltage translation
video-playlist (20 videos)