Shelling The Intel 8-bit Hex File Format

Intel 8-bit Hex File Format is the most common hex file format used in the world as far as I know. There is also Motorola Hex file format and maybe other. Creating applications with AVR-GCC we usually select ihex output file format what means Intel hex file format. Lets go through it and see whats inside. It is simple as 6 and 6 (six and six), because each Hex file line consists of six parts. And there can be 6 record types in hex file.

Lets go through all six parts of each line:

Intel Hex

  • Start code is always character ‘:’;

  • Byte count takes one byte (hex pair) indicating a number of bytes in a data field of the lin. Usually there are 16 or 32 bytes of data in each line;

  • Address takes two bytes (16 bits – four hex digits). Address shows the beginning of memory position for the data. 16 bits gives a limit of 64kilobytes. This is worked around by specifying higher bits via other record types;

  • Record type takes one byte (two hex digits). It defines the type of data field;

  • Data is a sequence of n bytes (2*n hex digits);

  • Checksum is one byte (two hex digits). It is a last byte in a line. It is calculated from fields: byte count, Address, record type and data and taking its Two’s complement . Start code and checksum itself isn’t included.

    Check sum calculation example:


    Taking all the data bytes above, we have to calculate the checksum based on the following hexadecimal values:

    04+0F+40+00+9F+4F+08+95 = 1DE

    The value is greater then we leave part which is less than FF,so we get DE.

    Then Twos complement is 100h-DE=22

In Intel Hex File Format there are six types of record types:

  • 00 – data record;

  • 01 – End of file record. Usually it is “:00000001FF”;

  • 02 – Extended Segment address record. This indicates segment base address when 16 bits is not enough for addressing memory;

  • 03 – Start segment address record. Indicates initial segment base address.

  • 04 - Extended Linear Address Record – allows 32 bit addressing.

  • 05 – Start Linear Address Record.

By concluding all of this:

Sample hex file:












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