When an NT instruction is executed, if the variable that was ON during the previous scan is turned OFF during the current scan, the NT instruction will execute only during the current scan. The NT instruction cannot execute on an initial scan, because the state of the previous scan is always considered to be OFF. Therefore, on an initial scan, the NT instruction will not be conducted even after the instruction is executed. The following example describes the features of the NT instruction.
Program Example
Point A
The variable (Start) turns OFF, and then the variable (Motor) turns ON.
Point B
After a scan is executed once, the variable (Motor) will be turned OFF.
Point C
The variable (Motor) remains OFF because the upward transition of the variable (Start) is not detected.
For the positive transition and negative transition instruction operands, you must pay attention when performing indirect addressing to each element, especially when an element is specifying an array or bit using variables. The variable in the operand of the previous execution is compared with the variable in the operand of the current execution, and then an instruction is executed. Therefore, if the variable value to be specified is different, the target for comparison will differ.