Register usage

VTAM® uses the general-purpose registers in the same fashion regardless of the type of session being used, and it uses them for a variety of purposes. VTAM frequently passes back return codes and parameter-list addresses in the registers. Refer to z/OS Communications Server: SNA Programmer's LU 6.2 Reference for a summary of how VTAM uses the registers.

The APPCCMD macroinstruction follows register usage of other RPL-based macroinstructions, including the requirement that register 13 point to an 18-word save area. VTAM does define some additional codes for LU 6.2 services. See the following sections for further information:

For information on evaluating register feedback, see Registers.
For information on register contents when using the ATTN exit, see Using the ATTN exit.

(For more details on handling VTAM errors and special conditions associated with the APPCCMD macroinstructions, see Handling errors.)