Use of the APPCCMD macroinstruction

The APPCCMD macroinstruction requests LU 6.2 services from VTAM®. Application programs use it to request services for a specific conversation.

Although the macroinstructions can be issued asynchronously, with OPTCD=ASY specified on the macroinstruction, most macroinstruction processing for a conversation is done synchronously. A conversation cannot, for example, have two SEND macroinstructions outstanding at any one time. The asynchronous nature of the APPCCMD macroinstruction applies to the application program as a whole. The application program can have multiple APPCCMD macroinstructions outstanding against several conversations. Several macroinstructions can be outstanding on a conversation. The application program uses the APPCCMD CONTROL=CHECK macroinstruction to get completion information from an asynchronous macroinstruction that VTAM has finished processing.

Refer to z/OS Communications Server: SNA Programming for information on asynchronous processing.

In error situations, an APPCCMD macroinstruction that abnormally deallocates a conversation or terminates its session can be issued while a previous APPCCMD macroinstruction completes.

When a macroinstruction completes, return code feedback information is contained in two RPL fields and two RPL extension fields. The RPL fields are used by all VTAM application programs. The RPL extension fields support only LU 6.2 functions.

There are two RPL fields:
  • RTNCD
  • FDB2
There are two RPL extension fields:
  • RCPRI
  • RCSEC
If the RTNCD and FDB2 fields are 0, the macroinstruction has completed successfully and the RCPRI and RCSEC fields have no meaning. If the RTNCD, FDB2=X'00', X'0B', respectively, they indicate conditional completion of the macroinstruction. You should inspect the RCPRI and RCSEC fields to determine what happened.
Other RPL extension fields return:
  • Security-level support information.
  • An indicator that a request for permission to send data has been received from a partner LU.
  • An indicator that error log data has been received.
  • An indicator that an FMH-5 has been received.
  • The conversation state.
  • An indicator that expedited data has been received.

For RECEIVE macroinstructions, the WHATRCV field in the RPL extension also contains feedback information.