l4 - 6.111 Lecture # 4 Ss Counting is a very important...

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Unformatted text preview: 6.111 Lecture # 4 Ss Counting is a very important function in the digital world, and it is done in a variety of ways Here is a 'ripple' counter using negative edge triggered T flip flops Count Sequence: The LSB is on the left in this diagram. It always toggles. The transition of 1 -> 0 of each 'bit' triggers a toggle of the next most significant bit 0 0 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 1 0 0 1 1 1 1 0 0 0 1 0 0 1 1 0 1 0 1 0 1 1 1 1 0 0 Here is why it is called a 'ripple' counter: The effect of each input transition must affect all bits, and it does this by rippling through from LSB to MSB An odd effect is that the transient count is always less than the true count. Can COUNT fast, but maybe can't be READ fast! 'Synchronous' counters use more logic to reduce the time to stable outputs. Here is a simplified version of the 4 bit 74LS163 counter Note that, while all bits of the synchrous counter are set very close to the same time, they may not be set at exactly the same time. This means that there is a rapidly changing transient state of the counter....
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This note was uploaded on 07/20/2009 for the course ELECTRICAL 6.111 taught by Professor Prof.dontroxel during the Fall '02 term at MIT.

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l4 - 6.111 Lecture # 4 Ss Counting is a very important...

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