INTRPRET →      RPL:     ACB field → ACB
                Note: ARG and NIB are mutually exclusive.
                ARG field = CID of session
                NIB field → NIB:
                     NAME field = symbolic name of LU
                     NETID field = symbolic network identifier of LU
                     LISTEND field = YES
                Note: ECB and EXIT are mutually exclusive.
                If ECB is used, only one is allowed.
                ECB field → external ECB
                ECB field = internal ECB
                EXIT field →  RPL exit routine
                BRANCH field = YES|NO
                AREA field → data to be interpreted
                RECLEN field = length of data to be interpreted
                AAREA field → work area for interpreted data
                AAREALN field = 8 or larger number
                OPTCD field = SYN|ASY
 
     Registers 0 and 15 = return codes
 
     RPL:
              RTNCD field = recovery action return code
              FDB2 field = specific error return code
              REQ field = request code (27)
              SSENSEI field = CPM|STATE|FI|RR|PATH|0
              SSENSMI field = system-sense modifier value (or 0)
              USENSEI field = user-sense value (or 0)
              RECLEN field = length of data received (if
                              (RTNCD,FDB2) = (X'00',X'05'),
                              RECLEN = total required length)