The output of the last shift register is fed to the input of the first register. 1000, the repeating pattern is: 1000, 0100, 0010, 0001, 1000 . Johnson counters are often favoured, not just because they offer twice as many count states from the same number of shift registers, but because they are able to self-initialise from the all-zeros state, without requiring the first count bit to be injected externally at start-up. 4-bit Johnson counter using counters pdf in digital electronics D-Type Flip Flops.
Synchronous Clock and Reset line shown. Note the inversion of the Q signal from the last shift register before feeding back to the first D input, making this a Johnson counter. 4-bit Overbeck counter using four D-Type Flip Flops. The propagation delay of a ring counter will be a constant regardless of the number of bits in the code.
The complex combinational logic of an adder can create timing errors which may result in erratic hardware performance. The disadvantage of ring counters is that they are lower density codes. N states, where N is the number of bits in the code, whereas an Overbeck counter can represent only N states and a Johnson counter can represent only 2N states. This may be an important consideration in hardware implementations where registers are more expensive than combinational logic.
John Wiley and Sons, 2005, p. This page was last edited on 25 August 2017, at 08:09. Digital Electronics questions and answers with explanation for interview, competitive examination and entrance test. Fully solved examples with detailed answer description, explanation are given and it would be easy to understand. Here you can find Digital Electronics interview questions with answers and explanation.
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