Hello Tom,
?
If you go further this way, that PDF might be useful (it was to me):
?
http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/370/DOS_VS/Rel_29_Nov73/GC33-5373-2_DOS_VS_Supervisor_and_IO_Macros_Rel_29_Nov73.pdf
?
And here's a book that you might consider buying (I did):
?
https://www.amazon.com/Dos-Assembler-Language-Kevin-McQuillen/dp/0911625313/
?
Among other things, it explains in simple terms how to perform I/O in DOS/VS assembler with files, whether they are SAM, ISAM, DAM or VSAM.
?
Cheers,
?
Rene FERLAND, Montreal
René Ferland