Delphi programming : Reading Intel Hex file

Here is the routine for read one line of Intel Hex file (file format for the Intel 8-bit only)

General Intel HEX format (8 bit)

Each record begins with a RECORD MARK field containing 03AH, the ASCII code for the colon (’ : ’) character.

Each record has a RECLEN field which specifies the number of bytes of information or data which follows the RECTYP field of the record. Note that one data byte is represented by two ASCII characters. The maximum value of the RECLEN field is hexadecimal ’FF’ or 255.


Each record has a LOAD OFFSET or ADDRESS field which specifies the 16-bit starting load offset of the data bytes, therefore this field is only used for Data Records. In other records where this field is not used, it should be coded as four ASCII zero characters (’0000’ or 03030303OH).


Each record has a RECTYP field which specifies the record type of this record. The RECTYP field is used to interpret the remaining information within the record. The encoding for all the current record types are:

’00’ Data Record <=We use this record
’01’ End of File Record <=We use this record
’02’ Extended Segment Address Record
’03’ Start Segment Address Record
’04’ Extended Linear Address Record
’05’ Start Linear Address Record

Each record has a variable length INFO/DATA field, it consists of zero or more bytes encoded as pairs of hexadecimal digits. The interpretation of this field depends on the RECTYP field.

Each record ends with a CHKSUM field that contains the ASCII hexadecimal representation of the two’s complement of the 8-bit bytes that result from converting each pair of ASCII hexadecimal digits to one byte of binary, from the RECLEN field to the last byte of the INFO/DATA field. Therefore, the sum of all the ASCII pairs in a record after converting to binary, form the RECLEN field to and including the CHKSUM field, is zero.

Example :

:1005AA00000102030405060708090A0B0C0D0E0F88
^----------- use for calculate check sum ----------^^^
|_|
Check sum__|
RECLEN = 0x10 = 16
ADDRESS = 0x05AA
RECTYPE = 00
DATA = 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F
CHKSUM = 0x88 = 256 -sum(0x00+..+0x0F)= 256- 0x78

type buffer=array of byte;  //assign as Dynamic array
var HexBuf:buffer;

function readline(HexLine:string; var Buf:buffer):integer;
var ADDR,count:integer;
 CHKSUM,SUMLINE,RECLEN,RECTYPE,DATA:byte;
 t:shortstring;
begin
 // Array length may be change, here is 100,000
 SetLength(HexBuf,100000);
 if HexLine[1]=':' then begin
  t:='$'+copy(HexLine,2,2);   // get length
  RECLEN:=strtoint(t);
  CHKSUM:=0;
  CHKSUM:=CHKSUM+RECLEN;
  t:='$'+copy(HexLine,4,4); // get address
  ADDR:=strtoint(t);
  CHKSUM:=CHKSUM+lo(ADDR)+hi(ADDR);
  t:='$'+copy(HexLine,8,2);
  RECTYPE:=strtoint(t);
  CHKSUM:=CHKSUM+RECTYPE;
  case RECTYPE of
   0:begin             // datablock
     count:=0;
     while (count < RECLEN) do begin
      t:='$'+copy(HexLine,10+2*count,2);
      DATA:=strtoint(t);
      CHKSUM:=CHKSUM+DATA;
      Buf[ADDR+count]:=DATA;
      inc(count);
     end;
     t:='$'+copy(HexLine,10+2*count,2);
     SUMLINE:=strtoint(t);
     end;
   1:begin   // end of file
      t:='$'+copy(HexLine,10,2);
      SUMLINE:=strtoint(t);
      result:=1;
     end;
     else
     begin
        result := -2;  // invalid record type
        exit;
     end;
    end; //case
  // test checksum
  DATA:=SUMLINE+CHKSUM;
  if (DATA<>0) then result:=-3; // checksum error
 end
 else result:=-1; // no record
end;

To use this routine


Here is an example demonstration how to use the above readline routine

procedure TForm1.Button1Click(Sender: TObject);
var Fname,line:string;
    Fp : textfile;
    ErrorCode:integer;
begin
    Fname:='test.hex';
    AssignFile(Fp,Fname); { File selected in dialog }
    Reset(Fp);
    while not eof(Fp) do
    begin
      Readln(Fp, line);{ Read first line of file }
      ErrorCode := readline(line,HexBuf);
      if (ErrorCode=0) then
      begin
       // Do some thing if read one line OK
       // such send data to serial port,parallel port etc.
      end
      else
      begin
       // Error handle here
       //  0 = No error
       // -1 = File not Intel Hex format
       // -2 = Invalid record type
       // -3 = Checksum error
       break;  // exit while loop
      end;
    end;
    CloseFile(Fp);
end;