RECEIVE →     RPL:     ACB field → ACB
                       ARG field = CID session
                       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 → input data area
                       AREALEN field = length of input data area
                       RTYPE field = (DFSYN|NDFSYN,DFASY|NDFASY,
                            RESP|NRESP)
                       OPTCD field = (SYN|ASY,
                            CA|CS|CONDCS
                            SPEC|ANY,
                            TRUNC|KEEP|NIBTK,
                            Q|NQ)
 
     Registers 0 and 15 = return codes
 
     RPL:     RTNCD field = recovery action return code
              FDB2 field = specific error return code
              REQ field = request code (35)
              SSENSEI field = CPM|STATE|FI|RR|PATH|0
              SSENSMI field = system-sense modifier value (or 0)
              USENSEI field = user-sense value (or 0)
              USER field = data from USERFLD in NIB used
                   to establish session
              SEQNO field = sequence number of input
              RESPOND field = (EX|NEX,FME|NFME,RRN|
                   NRRN,QRESP|NQRESP)
              ARG field = CID of session completing the
                   RECEIVE
              RTYPE field = type of input received
              RECLEN field = length of input data
              CONTROL field = DATA|BID|BIS|CANCEL|
                   CHASE|LUS|QC|RTR|QEC|
                   RELQ|RSHUTD|SBI|SHUTC|
                   SHUTD|SIGNAL
              SIGDATA field = signal data (if CONTROL =
                   SIGNAL)
              CHNGDIR field = (CMD|NCMD,|REQ|NREQ)
              BRACKET field = (BB|NBB,EB|NEB,CEB|NCEB)

         CHAIN field = FIRST|MIDDLE|LAST|ONLY
         CRYPT field = YES|NO
         CODESEL field = STANDARD|ALT
         OPTCD field = FMHDR|NFMHDR
         RPLURH field =3-byte user RH