To use a CTUD counter instruction, which requirement must be fulfilled?

In the context of using a CTUD (Count Up/Down) counter instruction within a programmable logic controller (PLC) programming environment, it is crucial that both the CTU (Count Up) and CTD (Count Down) instructions share the same instruction tag. This is because the CTUD instruction relies on a unified reference for counting; the up counter and down counter need to track the same variable to ensure accurate operation.

When both instructions utilize the same tag, they can effectively increment or decrement the count based on the defined conditions, allowing for a seamless operation of the counting process. Using different tags for CTU and CTD could lead to discrepancies where the two counters do not maintain a coherent relationship, ultimately causing incorrect count behavior.

This requirement ensures that the count is properly managed as demanded by the application, allowing the program to maintain accurate operational functionality when utilizing the CTUD instruction for varying scenarios requiring both counting up and down.