Linkage Conventions for the System Services

Callers must also use the following linkage conventions for all APPC/MVS system services:

Register 1 must contain the address of a parameter list, which is a list of consecutive words, each containing the address of a parameter to be passed. The last word in this list must have a 1 in the high-order (sign) bit.
Register 13 must contain the address of an 18-word save area.
Register 14 must contain the return address.
Register 15 must contain the entry-point address of the service being called.
If the caller is running in AR ASC mode, access registers 1, 13, 14, and 15 must all be set to zero.

On return from the service, general and access registers 2 through 14 are restored (registers 0, 1, and 15 are not restored).

Any high-level language that generates this type of interface can be used to invoke APPC/MVS callable services.

Two methods can be used to access the APPC/MVS system services.

The ATBCSS module from SYS1.CSSLIB can be link-edited with any program that issues APPC/MVS system services.
A program can issue the MVS LOAD macro for the APPC/MVS system service to obtain its entry-point address, and then use that address to call the APPC/MVS system service.