To get the specifications, you will need to obtain IBM’s Licensed Internal Program Interface (LIPI) documentation. I don’t see a link to order it in a quick search. You’ll probably need to contact your IBM representative to find out how to order it.
The last time I went after it, it was a US$500 set of manuals, but that was almost ten years ago. I thought I saw a more recent reference that said it was easier to get than that now.