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:
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;
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01 – End of file record. Usually it is â€œ:00000001FFâ€;
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 â€“ allows 32 bit addressing.
05 – Start Linear Address Record.
By concluding all of this:
Sample hex file: