Hexadecimal for register and memory values in ARM Architecture - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ trace

intermediate

Trace the hexadecimal value in a register after an addition

Given the ARM assembly instructions below, what is the hexadecimal value stored in register R1 after execution?

ARM Architecture

MOV R0, #0x1A
MOV R1, #0x2F
ADD R1, R1, R0

A 0x2F

B 0x45

C 0x49

D 0x3F

💡 Hint

Add the hexadecimal values in R0 and R1 carefully.

R0 holds 0x1A (26 decimal), R1 holds 0x2F (47 decimal). Adding 26 + 47 = 73 decimal, which is 0x49 in hexadecimal.

🧠 Conceptual

intermediate

Understanding memory address representation in hexadecimal

Why are memory addresses in ARM architecture commonly shown in hexadecimal format instead of decimal?

A Because hexadecimal numbers are easier to add than decimal numbers.

B Because hexadecimal aligns well with byte boundaries and is shorter to write than binary or decimal.

C Because decimal numbers are not supported by ARM processors.

D Because ARM architecture uses base 16 internally for all calculations.

💡 Hint

Think about how computers organize memory and how humans read numbers.

Hexadecimal groups bits in sets of four, matching byte boundaries, making it concise and easier to read than binary or long decimal numbers.

❓ identification

advanced

Identify the hexadecimal value stored at a memory address

An ARM processor reads the following 4 bytes from memory starting at address 0x1000: 0xDE, 0xAD, 0xBE, 0xEF. What 32-bit hexadecimal value does it represent assuming little-endian format?

A 0xEFBEADDE

B 0xDEADBEEF

C EDDAEBFEx0

D 0xBEEFDEAD

💡 Hint

In little-endian, the least significant byte is stored at the lowest address.

Little-endian stores bytes in reverse order: 0xDE at 0x1000 is the least significant byte, so the 32-bit value is 0xEFBEADDE.

❓ Comparison

advanced

Compare hexadecimal and binary representations of a register value

Register R2 contains the value 0x3C. Which of the following binary values correctly represents this hexadecimal value?

A 11110000

B 11000011

C 00001111

D 00111100

💡 Hint

Convert each hex digit to 4 binary bits.

Hex 3 is 0011 and C is 1100, combined as 00111100.

🚀 Application

expert

Calculate the memory offset in hexadecimal

An ARM instruction loads a value from memory address 0x2000 into a register. The instruction uses an offset of 0x1C. What is the final memory address accessed by the instruction?

A 0x201C

B 0x1DE4

C 0x1C20

D 0x202C

💡 Hint

Add the base address and the offset in hexadecimal.

0x2000 + 0x1C = 0x201C. Hex addition is similar to decimal but base 16.

Practice

1. What does the prefix 0x in a value like 0x1A3F indicate in ARM architecture?

easy

A. The value is a binary number

B. The value is in decimal format

C. The value is a memory address

D. The value is in hexadecimal format

Solution

1. Step 1: Understand the prefix meaning

   The prefix 0x is a standard notation used in computing to indicate that the following number is in hexadecimal (base 16) format.

2. Step 2: Differentiate from other formats

   Decimal numbers do not have this prefix, binary numbers use 0b, and memory addresses may or may not use this prefix but the prefix itself means hexadecimal.

3. Final Answer:

   The value is in hexadecimal format -> Option D

4. Quick Check:

   Prefix 0x means hexadecimal [OK]

Hint: Remember 0x means hex, not decimal or binary [OK]

Common Mistakes:

• Confusing 0x with decimal numbers
• Thinking 0x means binary
• Assuming 0x always means memory address

2. Which of the following is the correct way to write the hexadecimal value for decimal 255 in ARM assembly?

easy

A. 0xFF

B. FFx0

C. 255x0

D. 0b11111111

Solution

1. Step 1: Convert decimal 255 to hexadecimal

   Decimal 255 equals hexadecimal FF because 15*16 + 15 = 255.

2. Step 2: Write the correct hexadecimal notation

   Hexadecimal values start with 0x followed by digits and letters A-F, so 0xFF is correct.

3. Final Answer:

   0xFF -> Option A

4. Quick Check:

   Decimal 255 = 0xFF [OK]

Hint: Hex starts with 0x, then hex digits (0-9, A-F) [OK]

Common Mistakes:

• Writing the prefix after the digits
• Using decimal digits without 0x
• Confusing binary prefix 0b with hex

3. Given the ARM register value R0 = 0x1C, what is the decimal equivalent of this value?

medium

A. 12

B. 28

C. 44

D. 31

Solution

1. Step 1: Understand hexadecimal digits

   The value 0x1C has two hex digits: 1 and C. Hex digit C equals decimal 12.

2. Step 2: Calculate decimal value

   Calculate as (1 * 16) + 12 = 16 + 12 = 28.

3. Final Answer:

   28 -> Option B

4. Quick Check:

   0x1C = 28 decimal [OK]

Hint: Multiply first digit by 16, add second digit decimal [OK]

Common Mistakes:

• Treating hex digits as decimal directly
• Ignoring that C = 12 in decimal
• Adding digits without multiplying first by 16

4. An ARM instruction tries to load the value 0xG5 into a register. What is the problem with this hexadecimal value?

medium

A. The value is too large for a register

B. The prefix 0x is missing

C. Hexadecimal digits must be 0-9 or A-F; 'G' is invalid

D. Hexadecimal values cannot be loaded into registers

Solution

1. Step 1: Check valid hexadecimal digits

   Hexadecimal digits include 0-9 and letters A-F only. The letter 'G' is not a valid hex digit.

2. Step 2: Identify the error in the value

   Since 'G' is invalid, the value 0xG5 is not a valid hexadecimal number and will cause an error.

3. Final Answer:

   Hexadecimal digits must be 0-9 or A-F; 'G' is invalid -> Option C

4. Quick Check:

   Hex digits only 0-9, A-F [OK]

Hint: Hex digits only 0-9 and A-F, no other letters [OK]

Common Mistakes:

• Assuming any letter can be hex
• Thinking 0x prefix is missing
• Believing hex values can't be loaded into registers

5. You have a memory address 0x100 storing the value 0x2A. You want to add decimal 10 to this value and store it back. What is the new hexadecimal value stored at 0x100?

hard

A. 0x34

B. 0x3A

C. 0x20

D. 0x2F

Solution

1. Step 1: Convert the original hex value to decimal

   Value at 0x100 is 0x2A. Hex 2A = (2 * 16) + 10 = 32 + 10 = 42 decimal.

2. Step 2: Add decimal 10 to the value

   42 + 10 = 52 decimal.

3. Step 3: Convert the result back to hexadecimal

   52 decimal = 3 * 16 + 4 = 0x34 in hexadecimal.

4. Final Answer:

   0x34 -> Option A

5. Quick Check:

   42 + 10 = 52 decimal = 0x34 hex [OK]

Hint: Convert hex to decimal, add, then convert back to hex [OK]

Common Mistakes:

• Adding hex digits directly without conversion
• Confusing decimal and hex values
• Forgetting to convert result back to hex