How to Convert Hex to Binary in Assembly Language: A Step-by-Step Guide

Hexadecimal (hex) and binary are fundamental number systems in low-level programming. Hex (base-16) is a compact way to represent binary (base-2) data, making it easier for programmers to read and write machine-level instructions.

In assembly language, working with hex and binary is essential because:

• Registers store binary data, but debugging often requires a hex representation.
• Memory addresses and opcodes are frequently displayed in hex.
• Embedded systems rely on binary manipulation for hardware control.

In this guide, we’ll break down how to convert hex to binary in assembly language with practical examples.

Basics of Hexadecimal and Binary

Before diving into assembly, let’s recap hex and binary:

Hex (Base-16)	Binary (Base-2)
0	0000
1	0001
2	0010
3	0011
4	0100
5	0101
6	0110
7	0111
8	1000
9	1001
A (10)	1010
B (11)	1011
C (12)	1100
D (13)	1101
E (14)	1110
F (15)	1111

Key Rule:

• 1 hex digit = 4 binary bits (since 16 = 2⁴).
• To convert hex to binary, replace each hex digit with its 4-bit binary equivalent.

Why Convert Hex to Binary in Assembly?

In assembly language:
✔ Registers store binary values, but debugging tools display them in hex.
✔ Bitwise operations (AND, OR, SHIFT) require binary understanding.
✔ Hardware programming (e.g., microcontrollers) often uses binary configurations.

---

Step-by-Step Hex-to-Binary Conversion

Manual Conversion Example

Let’s convert 2F (hex) to binary:

1. Split 2F into two digits: 2 and F.
2. Replace each with its 4-bit binary equivalent:
   • 2 → 0010
   • F → 1111
3. Combine them: 2F (hex) = 00101111 (binary).

---

Hex-to-Binary Conversion in Assembly (x86/MASM)

Pseudo-Code Logic

1. Read a hex digit (ASCII input).
2. Convert ASCII to numeric value:
   • '0'-'9' → Subtract '0' (0x30).
   • 'A'-'F' → Subtract 'A' (0x41) and add 10.
3. Map to 4-bit binary and store in a register.
4. Print binary digits by shifting and masking.

Assembly Code Example (x86 MASM)

.model small  
.stack 100h  
.data  
    hexInput db 'A'   ; Sample hex digit  
    binaryOutput db 8 dup('0'), '$'  ; 8-bit binary result  
.code  
main proc  
    mov ax, @data  
    mov ds, ax  

    ; Convert hex digit to binary  
    mov al, hexInput  
    cmp al, '9'  
    jbe digit_0_to_9  
    sub al, 'A' - 10   ; A-F → 10-15  
    jmp convert  
digit_0_to_9:  
    sub al, '0'        ; 0-9 → 0-9  
convert:  
    mov cx, 8          ; 8 bits to process  
    lea si, binaryOutput  
convert_loop:  
    rol al, 1          ; Rotate left (MSB → CF)  
    mov bl, '0'  
    jnc store_bit  
    mov bl, '1'  
store_bit:  
    mov [si], bl  
    inc si  
    loop convert_loop  

    ; Print binary result  
    mov ah, 09h  
    lea dx, binaryOutput  
    int 21h  

    mov ah, 4Ch  
    int 21h  
main endp  
end main  

Explanation:

• Takes a hex digit ('A') and converts it to binary (1010).
• Uses bit rotation (ROL) to extract each bit.
• Stores the result as an 8-bit ASCII string.

---

Use Cases for Hex-to-Binary Conversion

• Debugging: Inspecting register values in binary.
• Embedded Systems: Configuring hardware registers.
• Network Protocols: Parsing binary packet headers.
• Game Development: Optimising bit-level operations.

---

[ALSO READ: How to convert Hexadecimal to Binary?]

FAQs

---

Conclusion

Understanding hex-to-binary conversion is crucial for low-level programming. By mastering this in assembly, you’ll gain deeper control over hardware and debugging.

Try it yourself! Use our AiCalculator.in Hex to Binary Tool to experiment with conversions. Happy coding!