CTU (Count Up) Ladder Logic Instruction

Definition

The Count Up instruction counts up by one every time the preceding logic transitions from false to true. The Counter.DN bit is set when the Accumulator reaches the Preset. The accumulator will continue to count even when the done bit is set. The CTU instruction can be paired with a CTD instruction referencing the same tag name. The overflow and underflow bits are set when the Accumulator exceeds the upper or lower limits.

List of arguments

COUNTER STRUCTURE             PRE DEFINED STRUCTURE

Tag Structure

  • BOOL             Counter.UP     Count up bit, set when instruction is enabled.
  • BOOL             Counter.DN    Count done bit, set when the accumulator reaches the preset.
  • BOOL             Counter.OV    Count overflow bit, set when the count exceeds the upper limit of 2,147,483,647. The accumulator will roll over to -2,147,483,648 and begins counting down.
  • BOOL              Counter.UN     Count overflow bit, set when the count exceeds the lower limit of -2,147,483,648. The accumulator will roll over to 2,147,483,647 and begins counting up.
  • DINT               Counter.PRE    Count Preset value, when the accumulator reaches the preset the .DN bit is set.
  • DINT               Counter.ACC   Count Accumulator value, keeps track of the current count.

Note: The CTU ladder instruction is reset with the RESET instruction referencing the CTU tag. The instruction could also be reset by moving a 0 into the Accumulator.