What are the HEX files
We know an interesting fact of microcontrollers or microprocessor that these understand only one language which is form of numbers in hexadecimal. What the language we use to write a program for any kind of microcontroller, it is ultimately converted into a special format under stable for them. This file contain useful information for the microcontroller operation in specific format is known as as hexfile. It is the duty of our compiler and assembler to make it.
The Intel HEX file is an ASCII text file having lines of numbers that follow the Intel HEX file format. In an Intel HEX file each line contains one HEX record. These records mean each line is made up of hexadecimal numbers which presentation of machine language code. The Intel HEX files are used to transfer the program code and data to microcontrollers which is stored in a ROM or EPROM of it. Thus most EPROM programmers or emulators uses Intel HEX files. Now we will discuss the HEX record format.
Record Format
It may be noted that an Intel HEX file may be composed of any number of HEX records. The format Record is such that each record is made up of five fields
that are arranged in the following sequence:
- : is the colon, every Intel HEX record starts with colon means every line in HEX file start with this symbol.
- ll is the
record length field which represents the number of data bytes (dd)
in this record.
- aaaa is the
address field which represents the starting address for subsequent data in
this record.
- tt is the
field represents the HEX record type, which may be one of the
following type:
00 - data record
01 - end-of-file record
02 - extended segment address record
04 - extended linear address record - dd is a data field that represents one byte of data. A record may
have multiple data bytes. The number of data bytes in the record must
match the number specified in the ll field of this record.
- cc is the checksum field represents the checksum of a particular record. The checksum is calculated by summing the values of all
hexadecimal digit pairs in a record modulo 256 and then taking the two's
complement.
Data Records
The Intel HEX file is
made up of any number of data records. It may be noted that one record is per line at the end the end of line characters ends the line. As an example the Data records appear as follows:
This record is decoded as follows:
:10246200464C5549442050524F46494C4500464C33
where:
- 10 is the number of data bytes in the record.
- 2462 is the address where the data are to be located in memory.
- 00 is the record type 00 (a data record).
- 464C...464C is the data.
- 33 is the checksum of the record.
Extended Linear Address Records (HEX386)
Extended linear address
records are also known as 32-bit address records and HEX386 records. These
records contain the higher 16 bits i.e. bits 16-31 of the data address. The
extended linear address record is usually composed of two data bytes and appears as
follows:
:02000004FFFFFC
where:
- 02 is the number of data bytes in the record.
- 0000 is the address field. For the extended linear address record,
this field is always 0000.
- 04 is the record type 04 (an extended linear address record).
- FFFF is the upper 16 bits of the address.
- FC is the checksum of the record and is calculated as
01h + NOT(02h + 00h + 00h + 04h + FFh + FFh).
When an extended linear
address record is read, the extended linear address stored in the data field is is applied to subsequent records of the Intel HEX file. The
linear address remains same until changed by another extended address
record of the hex file.
The absolute memory
address of a data record is obtained by adding the address field in the record
and the shifted address data of the extended linear address record. The
following example will make it clear.
Address from the data record's address field 2462Extended linear address record data field FFFF --------Absolute-memory address FFFF2462
Extended Segment Address Records (HEX86)
The Extended segment
address records which is also known as HEX86 records. It is composed of bits 4 - 19 of the data
address segment of record. The extended segment address record must have two data bytes
and it appears as follows:
where:
- 02 is the number of data bytes in the record.
- 0000 is the address field. For the extended segment address record,
this field is always 0000.
- 02 is the record type 02 (an extended segment address record).
- 1200 is the segment of the address.
- EA is the checksum of the record and is calculated as
01h + NOT(02h + 00h + 00h + 02h + 12h + 00h).
When an extended segment
address record is read, the extended segment address stored in the data field is applied to subsequent records of the Intel HEX file. The
segment address remains same until changed by another extended address
record.
The absolute memory
address of a data record in hex file is obtained by adding the address field in the record
and the shifted-address data of the extended segment address record. The
following example will make it more clear this process.
Extended segment address record data field 1200 --------Absolute memory address 00014462
End-of-File (EOF) Records
An Intel HEX file must
end with an end-of-file (EOF) record. The value of this record field must be 01 in the
record type field. An EOF record always appears as follows:
where:
- 00 is the number of data bytes in the record.
- 0000 is the address where the data are to be located in memory. The
address in end-of-file records is meaningless and is ignored. An address
of 0000h is typical.
- 01 is the record type 01 (an end-of-file record).
- FF is the checksum of the record and is calculated as
01h + NOT(00h + 00h + 00h + 01h).
Example Intel HEX File
Following is a piece of
assembly code:
LJMP
ORG 0030H
MOV TMOD,#20H
MOV TL1,#(-13) ;BAUD 2400
MOV TH1,#(-13)
SETB TR1
INCHAR: JNB
RI,INCHAR
CLR RI
MOV A,SBUF
CJNE A,#20H,NEXT
NEXT: CPL C
JNC LESS
CJNE A,#7FH,WAIT
LESS: MOV A,#2EH
WAIT: JNB TI,WAIT
CLR TI
OUT: MOV SBUF,A
SJMP INCHAR
END
Following is the complete HEX file for above code:
:03000000020030CB
:10003000759852758920758BF3758DF3D28E309833
:10004000FDC298E599B42000B35003B47F02742E2A
:090050003099FDC299F59980E593
:00000001FF
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