Move instruction (MOV) in PLC Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the MOV instruction do in PLC programming?

The MOV instruction copies a value from a source to a destination without changing the source value.

beginner

In a MOV instruction, what are the two main parts involved?

The source (where the value comes from) and the destination (where the value is copied to).

beginner

True or False: The MOV instruction changes the original value in the source address.

False. The MOV instruction only copies the value; it does not change the source.

intermediate

Why is the MOV instruction useful in automation?

It helps transfer data between registers or memory locations, allowing the program to use or update values easily.

beginner

If you want to save a sensor reading into a memory register for later use, which instruction would you use?

The MOV instruction to copy the sensor value into the memory register.

What happens when a MOV instruction executes in a PLC?

A It copies the source value to the destination.

B It swaps the source and destination values.

C It deletes the source value.

D It adds the source and destination values.

The MOV instruction copies the value from the source to the destination without changing the source.

Which of these is NOT a part of the MOV instruction?

A Source

B Value

C Destination

D Condition

MOV instruction involves source and destination; it does not require a condition to copy the value.

If you want to keep the original value but also use it somewhere else, which instruction helps?

A SUB

B ADD

C MOV

D MUL

MOV copies the value without changing the original, so you can use it elsewhere.

What type of data does the MOV instruction usually handle?

A Numeric values

B Only text strings

C Only Boolean values

D Images

MOV typically copies numeric values like integers or floats in PLC registers.

When is the MOV instruction typically used in a PLC program?

A To start a motor

B To transfer data between memory locations

C To stop a process

D To read sensor input directly

MOV is used to transfer or copy data between registers or memory locations.

Explain how the MOV instruction works in a PLC program and why it is important.

Think about moving data like moving an item from one box to another without removing it from the first box.

Describe a simple real-life example where you would use the MOV instruction in automation.

Imagine writing down a temperature reading to remember it later while the sensor keeps measuring.

Practice

1. What does the MOV instruction do in PLC programming?

easy

A. Compares two values and sets a flag

B. Copies a value from a source to a destination without changing the source

C. Deletes a value from memory

D. Adds two values and stores the result

Solution

1. Step 1: Understand the MOV instruction purpose

   The MOV instruction copies data from one place to another without altering the original data.

2. Step 2: Compare with other options

   Other options describe different instructions like addition, deletion, or comparison, which are not MOV's function.

3. Final Answer:

   Copies a value from a source to a destination without changing the source -> Option B

4. Quick Check:

   MOV copies value unchanged [OK]

Hint: MOV copies data without changing source [OK]

Common Mistakes:

• Thinking MOV adds or deletes data
• Confusing MOV with comparison instructions
• Assuming MOV changes the source value

2. Which of the following is the correct syntax for the MOV instruction in PLC programming?

easy

A. MOV source, destination

B. MOV(destination, source)

C. MOV source -> destination

D. MOV = source to destination

Solution

1. Step 1: Recall standard MOV syntax

   The MOV instruction syntax is typically written as MOV followed by source and destination separated by a comma.

2. Step 2: Evaluate other options

   Options A, B, and D use incorrect syntax formats not recognized in PLC MOV instructions.

3. Final Answer:

   MOV source, destination -> Option A

4. Quick Check:

   Correct MOV syntax uses comma [OK]

Hint: MOV uses source, destination format [OK]

Common Mistakes:

• Reversing source and destination order
• Using parentheses or arrows incorrectly
• Adding extra symbols like '='

3. Given the following PLC code snippet:

MOV 100, D0
MOV D0, D1
MOV D1, D2

What is the final value stored in register D2?

medium

A. D0

B. 0

C. 100

D. D1

Solution

1. Step 1: Trace the first MOV instruction

   MOV 100, D0 sets D0 to 100.

2. Step 2: Trace the second and third MOV instructions

   MOV D0, D1 copies 100 to D1; MOV D1, D2 copies 100 to D2.

3. Final Answer:

   100 -> Option C

4. Quick Check:

   Value 100 moves through D0 to D2 [OK]

Hint: Follow value moves step-by-step [OK]

Common Mistakes:

• Assuming D2 remains 0
• Confusing register names with values
• Ignoring the order of MOV instructions

4. Identify the error in this MOV instruction:

MOV D1 D2

What is the problem?

medium

A. MOV requires parentheses

B. Source and destination are reversed

C. MOV cannot move between registers

D. Missing comma between source and destination

Solution

1. Step 1: Check syntax of MOV instruction

   MOV requires a comma between source and destination to separate them.

2. Step 2: Verify other options

   Source and destination order is correct; MOV can move between registers; parentheses are not required.

3. Final Answer:

   Missing comma between source and destination -> Option D

4. Quick Check:

   Comma separates source and destination [OK]

Hint: Always separate source and destination with a comma [OK]

Common Mistakes:

• Omitting the comma
• Swapping source and destination
• Adding unnecessary parentheses

5. You want to copy the value from input register X10 to output register Y20 only if X10 is greater than 50. Which PLC code snippet correctly uses the MOV instruction with this condition?

hard

A. LD X10
GT 50
MOV X10, Y20

B. LD X10 > 50
MOV X10, Y20

C. CMP X10, 50
MOV X10, Y20

D. LD X10
MOV X10, Y20
IF X10 > 50

Solution

1. Step 1: Understand conditional MOV usage

   To move only if X10 > 50, first load X10, then check if greater than 50, then move.

2. Step 2: Analyze each option

   LD X10 GT 50 MOV X10, Y20 correctly loads X10, tests GT 50, then moves X10 to Y20. Others lack proper condition or order.

3. Final Answer:

   LD X10 GT 50 MOV X10, Y20 -> Option A

4. Quick Check:

   Condition before MOV ensures correct transfer [OK]

Hint: Check condition before MOV to control data transfer [OK]

Common Mistakes:

• Placing MOV before condition check
• Using incorrect comparison instructions
• Missing condition entirely