Use of plc edge instructions - Database & Sql Blog Articles

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The plc edge instruction refers to the rising edge instruction EU and the falling edge instruction ED:
1. The edge instruction operates on the bit logic value, so any operation result that is bit logic can be followed by an edge instruction such as I, Q, M, V, C, T, comparison instruction, etc.
2. Each edge instruction is independent of each other, and it is only related to the logical value of the bit being operated when the program is executed to the instruction;
3. After the program starts from RUN, when the edge instruction is executed for the first time, it always outputs 0, and writes the bit logic value of this time;
4. After each execution of the edge instruction, the program uses the previous bit logic value and the current bit logic value to determine the output result, and then write down the current bit logic value for the next use.
5. When the rising edge instruction has a logic value of 0 before the previous bit and the logic value of this bit is 1, the output is 1.
6. When the falling edge instruction has a logic value of 1 before the previous bit and the logic value of this bit is 0, the output is 1
7, not subject to edge instructions in the main program, subprogram location restrictions
8. If in the subroutine, the same scan is called multiple times in the same period, it does not affect the behavior of the edge instruction;
9, multiple scan cycles are only called once, and does not affect the behavior of the edge instructions;
10, 8 / 9 two instructions, the edge command is not affected by the scan cycle, only related to the last two executions.