A ring counter is a type of digital counter circuit that consists of a circular shift register where the output of one flip-flop serves as the input to the next flip-flop in the sequence. The key characteristic of a ring counter is that only one flip-flop output is high (1) at any given time, creating a rotating or cyclic pattern of states.
Ring counters are typically constructed using D flip-flops, and the number of flip-flops used determines the number of states in the sequence. For an n-bit ring counter, there will be n states in the cycle, and the sequence will repeat after reaching the last state.
Let's illustrate this with an example of a 4-bit ring counter. We have four D flip-flops labeled as FF0, FF1, FF2, and FF3. Each flip-flop is connected in a circular manner, as follows:
The output of FF0 is connected to the D input of FF1.
The output of FF1 is connected to the D input of FF2.
The output of FF2 is connected to the D input of FF3.
The output of FF3 is connected to the D input of FF0.
To initiate the sequence, all flip-flops are initially reset to 0. Then, when a clock pulse is applied, the data is shifted through the flip-flops. The process works as follows:
Initially, all flip-flop outputs are 0: (FF0=0, FF1=0, FF2=0, FF3=0).
After the first clock pulse, FF0 is set to 1, and all other flip-flops remain at 0: (FF0=1, FF1=0, FF2=0, FF3=0).
On the second clock pulse, the 1 in FF0 is shifted to FF1, while FF0 returns to 0: (FF0=0, FF1=1, FF2=0, FF3=0).
The process continues for subsequent clock pulses, rotating the 1 bit through the flip-flops: (FF0=0, FF1=0, FF2=1, FF3=0), (FF0=0, FF1=0, FF2=0, FF3=1).
Finally, after the fourth clock pulse, the 1 bit has reached FF3, and the sequence wraps around to its initial state: (FF0=1, FF1=0, FF2=0, FF3=0). The cycle then repeats.
The cyclic sequencing in a ring counter can be useful in various applications, such as generating repetitive patterns or serving as a simple state machine for control purposes. However, it's important to note that due to the cyclic nature of the sequence, a ring counter is not suited for applications requiring unique states and counting in a strictly sequential manner.