Read EDI-856 interface data in ABAP program

HI Experts,

I have a requirement to read the incomming EDI-856 interface data from ABAP program and generate an IDOC.  I have gone through few EDI-856 documents and theformat in which to read the data .

Request you to let me know the code logic , function module to use or if  you have any document which can help me in the development.

Thanks in advance

Regards

Santosh