REMOTE LOAD and DNC LINK PROTOCOLS

1.0 ESTABABLISHING COMMUNICATION

       1.1 PROGRAM IDENTIFICATION TRANSACTION

              The CNC shall request that the remote device use a particular
              program number as the file name for the next transfer request
              via the following command sequence:

              CNC                         REMOTE
              ===                         ======
              <DC2>  --->--->--->--->--->
                     <---<---<---<---<--- <DC1>
              [pgm #] --->--->--->--->--->
              <EOT>  --->--->--->--->--->

              Program names may be differentiated from programs in that the
              former are never more than eight (8) characters in length while
              the latter are defined to be not less than nine (9) characters
              long.

       1.2 PROGRAM TRANSFER REQUEST

              The following two (2) command sequences initiate program transfers
              between the CNC and the remote device. If a program name has not
              been associated with this transaction (see 1.1, above) the remote
              device shall prompt for operator input via its own display and keypad.

       1.2.1 TRANSFER FROM REMOTE TO CNC

              The CNC shall request a part-program text transfer from the
              remote device to the CNC via the command sequence:

              CNC                         REMOTE
              ===                         ======
              <DC1>  --->--->--->--->--->
                     <---<---<---<---<--- pgm text
                     <---<---<---<---<--- <EOT>

       1.2.2 TRANSFER FROM CNC TO REMOTE

              The CNC shall request a part-program text transfer from the
              CNC to the remote device via the command sequence:

              CNC                         REMOTE
              ===                         ======
              <DC2>  --->--->--->--->--->
                     <---<---<---<---<--- <DC1>
            pgm text --->--->--->--->--->
              <EOT>  --->--->--->--->--->
              <DC4>  --->--->--->--->--->

2.0 TRANSFER RECORD STRUCTURE

       2.1 REMOTE LOAD

              2.1.1 Part-program text length shall be less than or equal to 12000
              characters.

              2.1.2 Part-program number shall consist of up to six numeric
              characters with the charactrer string ";L" (hex 3B 4C) appended.

              2.1.3 The part-program text shall be transfered from the remote
              device to the CNC as one variab1e-length record of up to 12000
              bytes.

              2.1.4 Error detection shall be via Vertical Redundancy Checks
              (parity) performed on a character-by-character basis by the
              communication line hardware (UART's).

               ===========================
              = REMOTE LOAD RECORD FORMAT =
               ===========================

              +--------------------------------+-----+
              | up to 12000 bytes program text | EOT |
              +--------------------------------+-----+


       2.2 DNC LINK

              2.2.1 Part-program text length shall be greater than 12000 chracters.

              2.2.2 Part-program number shall consist of up to six numeric
              characters with the character string ";D" (hex 3B 44) appended.

              2.2.3 The part program text shall be transfered from the remote
              device to the CNC as multiple records of up to 256 bytes each.

              2.2.4 Error detection shall be via Vertical Redundancy Checks (parity)
              performed on a character-by-character basis by the communication
              hardware (UART's) and Horizontal Redundancy Checks (LRC)
              performed on each record by the communication software.

               ========================
              = DNC-LINK RECORD FORMAT =
               ========================

              +------------------------------+-----+-----+
              | up to 256 bytes program text | ETB | LRC |
              +------------------------------+-----+-----+


3.O SUSPENSION / RESUMPTION OF TRANSMISSION

       3.1 During transmission of the DATA portion of a record the recieving
       device (CNC or REMOTE, as the case may be) shall transmit a single
       "DC3" (X-OFF) character to temporarily suspend data transmission
       and a single "DC1" (X-ON) character to resume data transmission
       previously suspended via a "DC3" character.

       3.2 The transmitting device shall, within three (3} character times
       after reception of a .'DC3" (X-OFF} character, suspend further data
       transmission until (a), the subsequent reception of a "DC1" (X-ON}
       character or (b), the subsequent reception of a "DLE" (cancel}
       character.


4.O ERROR HANDLING

       4.1 REMOTE LOAD ERRORS

              4.1.1 Errors encountered during REMOTE LOAD shall be considered
              fatal and unrecoverable. Upon reception of a character
              with an invalid VRC bit (parity) the CNC will request that
              the remote device cancel transmission via the following
              command sequence:

              CNC                         REMOTE
              ===                         ======
              <DLE>  --->--->--->--->--->

       4.2 DNC LINK ERRORS

              4.2.1 Error recovery shall be via re-transmission of the record
              in error. The CNC shall request another record by
              transmitting a single ACK character to request the next
              record or by transmitting a single NAK character to request
              the same record. The command sequence is as follows:
              
              CNC                         REMOTE
              ===                         ======
       Same record:
              <NAK>  --->--->--->--->--->
                     <---<---<---<---<--- DATA
                     <---<---<---<---<--- <ETB>
                     <---<---<---<---<--- LRC

       Next record:
              <ACK>  --->--->--->--->--->
                     <---<---<---<---<--- DATA
                     <---<---<---<---<--- <ETB>
                     <---<---<---<---<--- LRC

       4.3 CANCEL SEQUENCE

              4.3.1 When necessary to prematurely terminate a REMOTE LOAD or
              DNC-LINK process the CNC shall request that the remote
              device cancel the current file transfer via the <DLE>
              (data link escape) character.

              4.3.2 Upon reception of the <DLE> (cancel) code the remote device
              shall cease transmisssion of data, discard the balance
              of the file, and wait for another transfer request.
              The command sequence is as follows:

              CNC                         REMOTE
              ===                         ======
              <DC3>  --->--->--->--->--->
              <DLE>  --->--->--->--->--->