Move instruction (MOV) in PLC Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of MOV instruction with integer values

What is the value of destination register after executing the MOV instruction below?

PLC Programming

MOV 123, D10

A D10 = 123

B D10 = 0

C D10 = MOV 123

D D10 = 10

💡 Hint

MOV copies the source value into the destination register.

The MOV instruction copies the source value (123) into the destination register (D10). So D10 will hold 123.

💻 Command Output

intermediate

MOV instruction with string data

What will be the result of the MOV instruction below assuming the PLC supports string moves?

PLC Programming

MOV "HELLO", S1

A S1 = ""

B S1 = "HELLO"

C S1 = MOV "HELLO"

D S1 = NULL

💡 Hint

MOV copies the entire string into the destination string register.

The MOV instruction copies the string "HELLO" into the string register S1.

🔧 Debug

advanced

Identify the error in MOV instruction

Which option shows a MOV instruction that will cause a syntax error?

A MOV 100 D10

B MOV D5, D10

C MOV #100, D10

D MOV 100, D10

💡 Hint

MOV instructions require a comma between source and destination.

Option A is missing a comma between source (100) and destination (D10), causing a syntax error.

🧠 Conceptual

advanced

Effect of MOV instruction on destination register

If the destination register D20 initially contains 50, what will be its value after executing MOV D10, D20 when D10 contains 200?

A D20 will be 0

B D20 will remain 50

C D20 will be 200

D D20 will be 250

💡 Hint

MOV overwrites the destination with the source value.

MOV copies the value from D10 (200) into D20, overwriting the previous value 50.

🚀 Application

expert

Using MOV to swap values with a temporary register

Given registers D1=10 and D2=20, which sequence of MOV instructions correctly swaps their values using D3 as temporary storage?

A 3,1,2,4

B 2,1,3,4

C 1,3,2,4

D 1,2,3,4

💡 Hint

Use a temporary register to hold one value while swapping.

First save D1 to D3, then move D2 to D1, then move D3 to D2. NOP is a no-operation placeholder.

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