HI Arun,
SAP has certain transactions that provides additional feature of barcode entry. You dont need an interface for converting barcode font to ascii, it is recognizable through this bar code field. This is enabled for MIGO transaction also. On making certain settings, (TCODE OAC5, OSS 301855), a dialog box pops up for barcode entry for the corresponding transaction. And then user can post goods movement in MIGO directly with the help of a barcode scanner without making any further changes. The handling of pop up for barcode entry and many such details are also taken care of through this barcode entry field.
To exploit this feature of MIGO using BAPI, you activate it using bar_code field of BAPI2017_GM_HEAD_01.