WRITE_HEX_File_Format.txt

function writeline(ADDR,RECLEN,RECTYPE:integer;
            var buf:buffer):string;
var i:integer;
 CHKSUM:byte;

begin
 CHKSUM:=0;
 result:=':'+inttohex(RECLEN,2)+
            inttohex(ADDR,4)+inttohex(RECTYPE,2);
 CHKSUM:=RECLEN+lo(ADDR)+hi(ADDR);
 for i:=0 to RECLEN-1 do begin
  result:=result+inttohex(buf[ADDR+i],2);
  CHKSUM:=CHKSUM+buf[ADDR+i];
 end;
 result:=result+inttohex(256-CHKSUM,2);
end;

function write_eof:string;
begin
 result:=':00'+'0000'+'01'+'FF';  // :00000001FF
end;


To test the above routine use this example

procedure TForm1.Button2Click(Sender: TObject);
var Fname,line:string;
    Fp : textfile;
    ErrorCode,StartAddr,ByteCnt:integer;
    A_Line,EOF_HEX:string;
begin

    StartAddr:=$0000;  // start address
    ByteCnt:=3;    // 3 bytes
    SetLength(HexBufOut,ByteCnt);
    HexBufOut[0]:=$01;
    HexBufOut[1]:=$02;
    HexBufOut[2]:=$03;

    Fname:='test1.hex';
    AssignFile(Fp,Fname); { File selected in dialog }
    Rewrite(Fp);
    // write 16 bytes in HexBuf
    A_Line:=writeline(StartAddr,ByteCnt,$00,HexBufOut);  
    EOF_HEX:=':00'+'0000'+'01'+'FF';// write end of HEX file
    writeln(Fp,A_Line);
    writeln(Fp,EOF_HEX);
    closefile(Fp);
end;