APPCCMD macroinstructions can pass back any of a large number of return codes in the RPL extension. Each individual macroinstruction description in the z/OS Communications Server: SNA Programmer's LU 6.2 Reference includes a list of applicable return codes. In addition to describing error situations, many of the return codes also indicate whether the error is likely to recur. For example, an RCPRI, RCSEC return code combination of X'0004', X'0001' on an ALLOC macroinstruction indicates that the macroinstruction failed because of a temporary condition. The application program can attempt to allocate the conversation again. Return codes also indicate whether data purging or truncation occurred in an error situation and whether attempts to send or receive data should be repeated.

The extent to which the application program screens return codes depends upon its needs and the extent of the error handling it must provide. Some of the return codes indicate temporary conditions. Therefore, you should analyze the possible return codes to determine which ones the application program should handle.

The mechanism for handling return codes depends on the application program. The application program can include inline code for dealing with selected return codes, or it can include error-handling subroutines. The primary return codes passed back in the RPL extension field RCPRI are multiples of four and can be used to index into a branch table.

VTAM® also uses feedback from an APPCCMD macroinstruction to pass other important information to the program. VTAM uses fields in the RPL extension to indicate to the application program that a conversation request has been received from a partner LU and that a request-to-send has been received from a partner LU. When an error is reported, a field in the RPL extension indicates whether error log data follows. The application program should check these fields and respond appropriately.