EdSim51 - Intel HEX

Intel HEX Format

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The EdSim51 Simulator handles machine code files in the Intel HEX format. You can load and save HEX files.

Now you can write C code for the 8051, using a C compiler for the 8051 such as Keil, and then import that code to the EdSim51 Simulator via the Intel HEX file format. You'll need to ensure your C compiler outputs an Intel HEX file. To see how to do this for Keil uVision, click here.

Intel HEX

Intel HEX is a standard format for writing machine code to a regular text file. An example of an Intel HEX file is shown below:

:10000000C29FD29EE587D2E7F587758920758DFD61
:10001000758BFDD28E7530617531627532637533C3
:10002000007830E6600EA2D092E7F599083099FD8D
:06003000C29980EF80FE82
:00000001FF

Apart from the colon at the beginning of each line, the file contains only numbers, in hexadecimal form (0 through F).

Each line contains a record. Each record is divided into six parts. The six parts are explained in the table below.

character 1	marker	Every record must begin with :
characters 2-3	length	The two bytes immediately after the colon state the number of machine code bytes in the record. Therefore, the maximum number of machine code bytes in a record is 256.
characters 4-7	address	Bytes 4 through 7 state the code memory address of the first machine code byte in the record.
characters 8-9	type	There are three types: 00 - record contains normal internal memory machine code. 01 - end of file - this should be the last record in the file - there are no machine code bytes with a 01 type record. 02 - indicates the record contains machine code for extended (external) memory - since the EdSim51 Simulator does not deal with external memory any 02 type records will be ignored (if such records exist a warning will be displayed when the file is loaded into the Simulator).
data begin at character 10	data	If there are any data bytes, they begin immediately after byte 9 - maximum number of bytes per record is 256.
last 2 characters	checksum	The last two bytes are a checksum that are used to detect errors in the preceding record bytes (excluding the colon). The checksum is calculated by adding all the bytes together. 8-bit addition (the 9th carry bit is ignored) is used. The checksum is then the difference between this 8-bit sum and 256. If you look at the end of file record in the above example (the last line) you will notice that adding up all the bytes (excluding the colon and the last two bytes which are the checksum) you get 1. Then subtract this from 256 and you get 255, which is FF in hex. As you can see, this is the checksum for that record. For more information, click here.

Loading Intel HEX Files

To load a HEX file, click the Load button and in the file chooser that appears, select the Intel HEX Files option from the
Files of Type: menu (as shown in the images above). Files with .h or .hex extension will be displayed.

Usually, HEX files are saved with .h or .hex extension. However, this is not a necessity. The EdSim51 Simulator scans every file as it is loaded. If the file meets the Intel HEX format (described above) it is then disassembled and displayed as assembly code. If the file is not in HEX format it is simply loaded as a text file.

The image opposite shows part of a disassembled Intel HEX file (it is, in fact, the disassembly of the HEX file shown above).

As can be seen, when a HEX file is disassembled, the original records are also displayed, embedded in the assembly code as comments.

Saving Intel HEX Files

Click on the Save button to save a file. In the window that opens, the user can select, from the Files of Type: menu, one of three choices.

Assembly Files - The assembly source code is saved without modification. It is saved as a text-only file.
Intel HEX Files - The machine code in code memory is saved to a text file in Intel HEX format (format explained above).There are two important points to be remembered when saving in HEX format:
- Usually, when writing assembly code, the programmer uses labels, assembler directives (example, PSW for the address of the Program Status Word), etc. None of this information is saved in HEX format. HEX format saves only the code that resides in code memory. The EdSim51 Simulator keeps track of what areas of code memory the programmer is using and only those areas are saved in the HEX file.
- If the source code has not assembled without errors it cannot be saved in HEX format. If you attempt to save code that is not assembled in HEX format an error message will be displayed.
Assembly Files and HEX Files - Perhaps you want to save your code in both formats. If so choose this option. You need only provide the name of one of the files to be saved. Two separate files are then saved; one without modification and with either a .a or .asm extension, the other in HEX format with either a .h or .hex extension. The name of the second file is generated automatically from the first. For example, if you provide example.asm as the file name, the second file name will be example.hex. If you provide example.hex as the file name, the second file name will be example.asm.

Write C code for the 8051 and import the machine code into the EdSim51 Simulator.

You can write C program for the 8051 using one of many 8051 C compilers. You will need to have the C compiler output a HEX file. You can then open this HEX file and test your program in the EdSim51 Simulator.

If, for example, you are using Keil's uVision IDE you can get a HEX file output by going to Project->Options for Target and clicking on the Output tab. Check the Create HEX File checkbox and click Enter.