环形计数器是一种由连接到移位寄存器中的触发器组成的计数器。它有两种类型：
1. 直环计数器：
直环计数器是一种环形计数器，其中最后一个触发器的输出连接到第一个触发器的输入。它在环周围循环单个“0”或“1”位。
2. 扭环计数器：
Twisted Ring counter 是一种环形计数器，其中最后一个移位寄存器的输出的补码连接到第一个寄存器的输入。它在环周围循环 1s 后跟 0s 的流。
直环和扭环计数器的区别：
| STRAIGHT RING COUNTER | TWISTED RING COUNTER |
|---|---|
| It connects the output of the last shift register to the input of first shift register. | It connects the complement of output of the last shift register to the input of the first register. |
| It is known as One hot counter. | It is known as Walking ring counter. |
| It circulates a single bit (0 or 1) around the ring. | It circulates stream of 1 followed by stream of 0. |
| PRESET is used in first shift register. | PRESET is not used in twisted ring counter. |
| CLEAR is used for last (n-1) flip-flops. | CLEAR is used for all flip-flips in it. |
| It is used in successive approximation and stepper motor control. | It is used in phase shift or function generator. |