This document provides instructions for writing and testing a program to latch an output using a PLC. It includes 3 chapters: 1. Writing a ladder logic program using contacts to latch an output and converting it for the PLC. 2. Transferring the program to a virtual PLC. 3. Testing the latched output behavior and alternatives using SET and RST instructions to hold the output status.

1. Standard Program
Chapter 1 Latched Output Program
Write the program which latches the output.
CAUTION
Click the ladder program area to enable operation. The title bar will turn blue.
Key operations are not enabled when the title bar and menu items are grayed out.
1 Click [Edit Ladder] button on the remote control.
2 Input the program below.
Place the cursor inside the ladder diagram on the left hand side and begin to input data.
These symbols can be input by pressing the following keys.
3 Let's convert the program you have written into a form the PLC can recognize.
Press the [F4] key.
The background of the program is changed from gray to white.
The program has been converted.
If the program has not been input properly, a conversion error message is displayed.

2. Standard Program
Chapter 2 Program Transfer to PLC
Write the program you have created to the PLC.
An actual PLC is not required because a virtual FX Series PLC is already in your computer.
1 The program can be written to the PLC by selecting "Online" - "Write to PLC" in the ladder program area.
2 When the message 'Write completed. The simulation will start.' is displayed, select [OK].
The PLC starts to operate.
The 'RUN' indicator lamp should be lit in the I/O monitor display area of the PLC.
If it is not lit, the PLC is not operating.
Next, let's simulate the program you have created.
Go to the next step.

3. Standard Program
Chapter 3 Confirm Latched Output Program Operation
Can you light the operation status lamp using your program?
1 When [PB1] (X20) on the operation panel is pressed, the lamp Operating (Y0) is lit.
2 Even when [PB1] (X20) on the operation panel is released, the lamp remains lit.
The output ON status is held by the lamp Operating (Y0) contact.
In this operation, the output is 'latched'. (Latched output program)
3 In this program, if the [SW1] (X24) is set ON, the lamp cannot be lit no matter if the drive input [PB1] (X20) is
ON or not. Switch [SW1] (X24) takes precedence over [PB1] (X20).
Let's suppose [PB1] (X20) was a start input and [SW1] (X24) was a stop input.
Can you think of some practical situations where this could be useful?
4 In the program below, the operating lamp comes ON when [PB1] (X20) is pressed and will remain lit if [PB1]
(X20) is released.
If [SW1] (X24) is turned ON, the lamp will be turned OFF.
However, if both [PB1] (X20) and [SW1] (X24) are ON, the lamp Operating (Y0) will be lit.
The input [PB1] (X20) takes precedence over [SW1] (X24).
This is an extra programming exercise.
When confirming the operation, start to program after selecting "Project" - "New project".
Did you get it right?
No Yes (Go to the next step.)

4. Standard Program
Chapter 4 SET/RST Instruction
Another method for holding the output status is the 'SET instruction'.
Let's use the 'SET instruction'.
1 Click [Edit Ladder] button on the remote control.
2 Select "Project" - "New".
3 Let's input a program.
1) Place the cursor inside the ladder diagram on the left hand side.
Press the [F5] key.
In the 'Enter comment' dialog box, enter X20 and click [OK].
Press the [F8] key.
In the 'Enter symbol' dialog box, enter SET Y0 and click [OK].
(Use a space between SET and Y0)
2) Write the program on the second line.
Press the [F5] key.
In the 'Enter symbol' dialog box, enter X21 and click [OK].
Press the [F8] key.
In the 'Enter symbol' dialog box, enter RST Y0 and click [OK].
(Use a space between RST and Y0)
The program should look like this. Make sure that yours is correct.
4 Let's convert the program you have written into a form the PLC can recognize.
Press the [F4] key.
5 The program can be written to the PLC by selecting "Online" - "Write to PLC".
Did you get it right?
No Yes (Go to the next step.)

5. Standard Program
Chapter 5 Confirm SET/RST Instruction Operation
Let's light a lamp.
1 When [PB1] (X20) on the operation panel is pressed, the lamp Operating (Y0) is lit.
2 When [PB1] (X20) on the operation panel is released, the lamp remains lit.
The output status of the lamp Operating (Y0) is held by the SET instruction.
3 When [PB2] (X20) on the operation panel is pressed, the lamp Operating (Y0) is reset and extinguished.
In PLC programs, SET/RST instructions are often used to hold output status or results.
This instruction can be used any number of times for the same output so that the problem caused by dual coils can
be solved.
Did you get it right?
No Yes (Go to the next step.)