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PLC: Program to Delay Turning ON a Work Bit (2)

FAQ No. FAQ01470

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How do I write a program to delay turning ON a work bit for 1 scan after an input A turns ON and keep the work bit ON for only 1 scan?


As shown in Figure 1, the program delays for 1 scan after input A turns ON, and then turns ON work bit W2.00 for only 1 scan, as shown in Figure 2.

Figure 1

Ladder Programming

Figure 2

Operation: Refer to Figure 3

1.When input A (IR 0.00) turns ON, the DIFFERENTIATE UP (DIFU) instruction turns ON work bit IR 200.00 for only 1 scan.

2.When IR 200.00 turns OFF in the next scan, the DIFFERENTIATE DOWN (DIFD) instruction turns ON work bit IR 200.01 for only 1 scan.

Figure 3

3.Turns ON for only 1 scan.

Data Trace Results

Figure 4

IR00000: Input A (IR 0.00), IR20000: Internal bit IR 200.00
IR20001: Internal bit IR 200.01

Applications of this Programming

This programming technique to delay turning ON a work bit for 1 scan after another bit's status changes (i.e., turns ON) and then turn on the work bit for only 1 scan can be used for time limit control between a data output signal and strobe signal in parallel transmissions.

Example of Time Limit Control in Parallel Transmissions

"Transmission request input from a terminal device turns ON" to "Parallel data (n bits) is output".

to "Strobe signal (1 bit) turns ON after 1 scan".

Application Conditions for this Programming

The signal from the device must meet the following time-related conditions.

The time period required between the parallel data and strobe signal must be less than the Programmable Controllers' shortest scan time.

Note:When using a CS/CJ-series Programmable Controller, a differentiated instruction --|↑|-- and CONDITION OFF instruction (DOWN) can also be used for the same purpose as the above instructions.