Register and data table concepts in PLC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a register named 'R1' in the PLC program.

PLC Programming

MOV 0, [1]

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AR1

BD1

CM1

DT1

Attempts:

3 left

💡 Hint

Common Mistakes

Using data table addresses like D1 instead of register R1.

Confusing timers (T1) or memory bits (M1) with registers.

The register 'R1' is used to store data. MOV 0, R1 initializes it to zero.

2fill in blank

medium

Complete the code to move the value from register R2 to data table D5.

PLC Programming

MOV [1], D5

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AR2

BT2

CM2

DD2

Attempts:

3 left

💡 Hint

Common Mistakes

Using D2 as source instead of R2.

Using memory bit M2 or timer T2 incorrectly.

MOV R2, D5 moves the value stored in register R2 into data table address D5.

3fill in blank

hard

Fix the error in the code to correctly add the value in register R3 to data table D7.

PLC Programming

ADD [1], D7

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AD3

BR3

CM3

DT3

Attempts:

3 left

💡 Hint

Common Mistakes

Using data table D3 as source instead of register R3.

Using memory bit or timer addresses incorrectly.

ADD R3, D7 adds the value in register R3 to the value in data table D7.

4fill in blank

hard

Fill both blanks to create a loop that increments register R4 until it equals 10.

PLC Programming

INC R4
LD [1]
CMP [2], 10
JNE LOOP_START

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AR4

BD4

CR5

DM4

Attempts:

3 left

💡 Hint

Common Mistakes

Using different registers or data table addresses for load and compare.

Using memory bits instead of registers.

LD R4 loads the value of register R4, CMP R4, 10 compares it to 10 to control the loop.

5fill in blank

hard

Fill all three blanks to create a data table that stores squares of numbers 1 to 5.

PLC Programming

FOR [1] = 1 TO 5
MOV [2], [1]
MUL [2], [2]
MOV [2], D[1]
NEXT

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Ai

BR10

CR11

DR12

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names or registers.

Not moving the squared value to the correct data table address.

Loop variable 'i' controls the loop. R10 holds the number, which is squared in R10 and moved to data table D1 to D5.

Practice

1. What is the primary purpose of a register in PLC programming?

easy

A. To store a single piece of data or value

B. To organize multiple registers into a table

C. To execute a sequence of instructions

D. To display output on a screen

Solution

1. Step 1: Understand what a register holds

   A register stores one piece of data, like a number or a status.

2. Step 2: Differentiate registers from data tables

   Data tables group many registers, but a single register holds only one value.

3. Final Answer:

   To store a single piece of data or value -> Option A

4. Quick Check:

   Register = single data storage [OK]

Hint: Registers hold one value; tables hold many [OK]

Common Mistakes:

• Confusing registers with data tables
• Thinking registers execute instructions
• Assuming registers display output

2. Which of the following is the correct syntax to declare a data table named DataTable1 with 10 registers in a typical PLC program?

easy

A. DataTable1: ARRAY[1..10] OF INT;

B. DataTable1 = {10 registers};

C. DECLARE DataTable1 WITH 10 REGISTERS;

D. DataTable1: INT[10];

Solution

1. Step 1: Identify correct array declaration syntax

   In PLC, arrays are declared with ARRAY and index range, e.g., ARRAY[1..10] OF INT.

2. Step 2: Check each option's syntax

   DataTable1: ARRAY[1..10] OF INT; matches standard PLC array declaration; others are incorrect or invalid syntax.

3. Final Answer:

   DataTable1: ARRAY[1..10] OF INT; -> Option A

4. Quick Check:

   ARRAY[1..10] OF INT is correct syntax [OK]

Hint: Use ARRAY with index range and type for tables [OK]

Common Mistakes:

• Using curly braces instead of ARRAY
• Missing index range in declaration
• Incorrect keyword usage like DECLARE

3. Given the following PLC code snippet, what is the value stored in DataTable1[3] after execution?

DataTable1: ARRAY[1..5] OF INT := [10, 20, 30, 40, 50];
DataTable1[3] := DataTable1[2] + DataTable1[4];

medium

A. 30

B. 60

C. 50

D. 70

Solution

1. Step 1: Identify initial values in DataTable1

   DataTable1 = [10, 20, 30, 40, 50], so DataTable1[2] = 20 and DataTable1[4] = 40.

2. Step 2: Calculate new value for DataTable1[3]

   DataTable1[3] = 20 + 40 = 60 after assignment.

3. Final Answer:

   60 -> Option B

4. Quick Check:

   20 + 40 = 60 [OK]

Hint: Add values at indexes 2 and 4 for index 3 [OK]

Common Mistakes:

• Using old value of DataTable1[3]
• Adding wrong indexes
• Confusing array indexing starting point

4. Identify the error in this PLC code snippet that tries to assign a value to a register:

Register1: INT;
Register1 := 100
Register2 := 200;

medium

A. Incorrect assignment operator used

B. Missing semicolon after first assignment

C. Register2 is not declared before use

D. Register1 should be declared as ARRAY

Solution

1. Step 1: Check declarations of registers

   Register1 is declared, but Register2 is used without declaration.

2. Step 2: Verify syntax and declarations

   Missing semicolon after first assignment is an error but not the main one; Register2 usage without declaration causes error.

3. Final Answer:

   Register2 is not declared before use -> Option C

4. Quick Check:

   Undeclared variable usage = error [OK]

Hint: Always declare registers before assigning values [OK]

Common Mistakes:

• Ignoring undeclared variables
• Assuming semicolon is optional
• Confusing assignment operator

5. You want to track the temperature readings from 8 sensors using registers and a data table. Which approach is best to organize this data efficiently?

hard

A. Create a data table with 1 register and update it 8 times

B. Create 8 separate registers named Temp1 to Temp8

C. Use a single register to store all 8 temperatures as a string

D. Use a data table (array) of 8 registers named TempSensors

Solution

1. Step 1: Consider data organization for multiple sensors

   Using a data table (array) groups related data efficiently and simplifies access.

2. Step 2: Evaluate options for best practice

   Separate registers are harder to manage; single register as string complicates processing; updating one register repeatedly loses data.

3. Final Answer:

   Use a data table (array) of 8 registers named TempSensors -> Option D

4. Quick Check:

   Data table groups multiple registers efficiently [OK]

Hint: Group similar data in arrays for easy management [OK]

Common Mistakes:

• Using many separate registers instead of array
• Storing multiple values in one register as string
• Overwriting single register repeatedly