🚀 go-pugleaf

The information about channel programming is spread out over several manuals;
the place I learned most about it was other people's programs.  There is an
old manual called OS/VS2 System Programming Library: Data Management (GC26-
3830) that describes IOBs and how to issue EXCP.  I think there is still a
manual with a title similar to that, so it shouldn't be difficult to find.
The best place to find the CCW layout and the commands is the Reference
Summary (GX20-1850), which also lists the reference manual numbers so you
can refer to them for more information.  The best place I have seen that
describes the CCWs for 3270 devices is the VM Systems Programmer's Guide,
under the description of Diagnose 58.  Generally, if you are going to be
working in MVS, you are going to be issuing EXCP to run your channel program,
so you should investigate the IOB, ECB, CCW, CSW and CAW, and don't forget
MACRF=E in your DCB.  Of course, doing it in MVS first gives you a REAL
appreciation for the way it is done in CMS, so I recommend that approach
first.  After that, blow your 3270 away a few times with DIAG58, and try
some disk I/O with DIAG18.  Most important to know your CCWs, and how to
interpret the CSW status bits.

R;