The difference between HEX and BIN files in microcontrollers

In microcontroller development, HEX (Intel HEX) and BIN (binary) files are two common formats used to store and transfer firmware. Here’s a breakdown of their differences, purposes, and when to use each:

1. Binary (BIN) File

• Format: Raw binary data (0s and 1s) representing the exact machine code to be written to the microcontroller's flash memory.

• Contents:

  • Pure executable code + data (no additional metadata).

  • Addresses are implied by the file offset (e.g., the first byte is loaded at the base address).

• Pros:

  • Smaller size (no overhead).

  • Directly writable to flash memory (e.g., via STM32 bootloader).

• Cons:

  • No address/location information (must be specified separately during flashing).

  • No checksums or error detection.

• Typical Use Cases:

  • Flashing via tools like stm32flash, OpenOCD, or USB DFU.

  • OTA (Over-the-Air) updates where bandwidth matters.

2. Intel HEX (HEX) File

• Format: ASCII text file with addresses, data, and checksums in a standardized format.

• Contents:

  • Each line contains:

    • Start code (:).

    • Byte count, address, record type (data, EOF, etc.).

    • Data payload + checksum.

  • Supports non-contiguous memory regions (gaps are handled explicitly).

• Pros:

  • Self-contained address information.

  • Built-in error detection (checksums).

  • Human-readable (can be inspected with a text editor).

• Cons:

  • Larger file size (due to ASCII encoding and metadata).

  • Requires parsing before flashing.

• Typical Use Cases:

  • Debugging (easier to analyze).

  • Flashing via IDEs (Keil, IAR, STM32CubeProgrammer).

  • EEPROM programming (where addresses matter).

Key Differences

When to Use Which?

• Use BIN:

  • When flashing via bootloaders (e.g., STM32 UART/USB DFU).

  • For OTA updates (minimizes transmission size).

  • When the target address is known and fixed.

• Use HEX:

  • When debugging or analyzing firmware.

  • When flashing via IDEs (e.g., STM32CubeIDE automatically generates HEX).

  • For EEPROM or non-contiguous memory layouts.

Conversion Between HEX and BIN

• HEX to BIN:
  Use tools like objcopy (GNU Arm Embedded Toolchain):

  sh

   

  arm-none-eabi-objcopy -I ihex -O binary firmware.hex firmware.bin

• BIN to HEX:
  Specify the base address (e.g., 0x08000000 for STM32 flash):

  sh

   

  arm-none-eabi-objcopy -I binary -O ihex --adjust-vma 0x08000000 firmware.bin firmware.hex

Example HEX File Snippet

:1000000048000020A1010008AD010008B1010008C4
:10001000B5010008B9010008000000000000000020
:0400200000000000B8
:00000001FF

• :10 = 16 bytes of data.

• 0000 = Address offset.

• 00 = Record type (data).

• C4 = Checksum.

STM32-Specific Notes

• STM32CubeIDE: By default generates both .hex and .bin files (configurable in project settings).

• Flashing Tools:

  • ST-Link Utility: Supports both HEX and BIN.

  • STM32CubeProgrammer: Prefers HEX but accepts BIN (requires address input).

Summary

• BIN: Simpler, smaller, but lacks metadata. Best for production flashing.

• HEX: Self-documenting, safer for debugging. Used during development.

Choose based on your toolchain and requirements!