What must both CTU and CTD instructions share in order to enter a CUD counter instruction?

The correct choice is based on the requirement that both the CTU (Count Up) and CTD (Count Down) instructions must utilize the same instruction tag when they interact with a CUD (Count Up/Down) counter instruction.

The instruction tag serves as an identifier that links the CTU and CTD to the same counter. This means that both instructions can appropriately increment or decrement the same count, reflecting a unified operation on the same counter instance within a control system. Without the same instruction tag, there would be no synchronization between the CTU and CTD, thus failing to provide coherent and meaningful count tracking in the program’s logic.

Establishing a shared instruction tag ensures that all operations related to counting are managed under a single identifier, which is critical for accurate data handling and maintaining the integrity of counting processes within programmable logic controllers.