A Johnson counter is a type of digital counter circuit used in electronics and digital logic design. It's a specific implementation of a shift register with feedback that produces a cyclic sequence of binary states. The unique shifting pattern of a Johnson counter involves shifting the bits in such a way that only one bit changes its state at each clock cycle, creating a "walking" or "cascading" effect through the bits.
A Johnson counter is typically composed of a series of flip-flops connected in a ring or loop configuration. The output of each flip-flop is fed into the next flip-flop's input, and the last flip-flop's output is connected to the first flip-flop's input. This feedback loop creates the cyclic behavior characteristic of a Johnson counter.
The shifting pattern of a Johnson counter is designed in a way that only one bit changes its state from 0 to 1 or from 1 to 0 during each clock cycle. The direction of shifting (left or right) depends on the specific implementation, but the essential characteristic is that the transition between states is always controlled so that only one bit changes, and the rest of the bits remain unchanged.
For example, let's consider a 4-bit Johnson counter with an initial state of 0001. The shifting pattern would look like this:
Clock 1: 0001
Clock 2: 1000
Clock 3: 1100
Clock 4: 0110
Clock 5: 0011
Clock 6: 1001
Clock 7: 0100
Clock 8: 0010
In this pattern, you can see that at each clock cycle, only one bit changes its state, and the rest of the bits follow suit in a cascading manner. This type of shifting pattern is useful in various applications, such as generating timing sequences, controlling LEDs, or creating rotating visual effects in displays.
It's worth noting that Johnson counters are just one example of shift registers with specific shifting patterns. Other shift register configurations, like ring counters and linear-feedback shift registers (LFSRs), also have unique shifting patterns and find applications in various digital logic and communication systems.