Which counter type counts only downward?

A down counter is specifically designed to count in a descending manner, meaning it reduces its count with each clock pulse received. This is in contrast to other counter types, such as an up counter, which increments its count. The down counter effectively tracks counts in reverse order, which can be particularly useful in various applications such as timers, countdowns, and control systems where tracking remaining time or resources is necessary.

The decade counter, which counts in a sequence of ten, can count both up and down based on how it is configured and does not solely count downward. Similarly, a synchronous counter, which can be either an up or down counter depending on its design, uses a specific clock signal to update all flip-flops simultaneously but does not limit its counting direction. Therefore, the distinctive characteristic of a down counter is its exclusive downward counting function, making it the correct choice for this question.