Performing I/O in 31-bit addressing mode

Programs in 31-bit addressing mode sometimes need to use 24-bit addressing mode programs to perform an I/O operation.

A 31-bit addressing mode program can perform an I/O operation by:
  • Using VSAM, QSAM, BSAM, BPAM and BDAM services that accept callers in either 24-bit or 31-bit addressing mode. (z/OS DFSMS Using Data Sets describes these services and shows examples. The functions that require 24-bit mode are ISAM, some BDAM functions and BSAM and QSAM with a TSO terminal or IBM® 3886 or 3890 Document Processor.)
  • Using the EXCP macro. All parameter lists, control blocks, CCWs, virtual IDAWs, and EXCP appendage routines must reside in virtual storage below 16 megabytes. See Using the EXCP macro for a description of using EXCP to perform I/O. CCWs can reside above the 16 MB line and virtual IDAWs can point above the 16 MB line or above the 2 GB bar.
  • Using the EXCPVR macro. All parameter lists, control blocks, CCWs, IDALs (indirect data address lists), and appendage routines must reside in virtual storage below 16 megabytes. See Using EXCPVR for a description of using EXCPVR to perform I/O. CCWs can reside above the 16 MB line and virtual and real IDAWs can point above the 16 MB line or above the 2 GB bar.
  • Invoking a routine that executes in 24-bit addressing mode as an interface to the 24-bit access methods, which accept callers executing in 24-bit addressing mode only. See Establishing linkage for more information about this method.
  • Using the method shown in Figure 1.
Parent topic: Understanding 31-bit addressing