text: I don't know AVR, but I can say it probably is a register shift left, as that's what it is in C.  \n\nDDD5 would be a register of some length, and 1<<DDD5 would shift each bit by one, adding a zero at the end.  I'll look further and try to find a source.\n\n--\nEdit:  Found one.  The first source answers your question directly, the second one has a huge list of resources for you.\n--