    NWG/RFC# 732                                  DAY 13-Sep-77 18:38  41762
    Data Entry Terminal Option

    Network Working Group                                           John Day
    Request for Comments: 732
    NIC: 41762                                             12 September 1977

    Obsoletes: 731

                       Telnet Data Entry Terminal Option

    1.  Command Name and Code:

      DET             20

    2.  Command Meanings

      IAC WILL DET

        The sender of this command REQUESTS or AGREES to send and receive
        subcommands to control the Data Entry Terminal.

      IAC WONT DET

        The sender of this command REFUSES to send and receive subcommands
        to control the Data Entry Terminal.

      IAC DO DET

        The sender of this command REQUESTS or AGREES to send and receive
        subcommands to control the Data Entry Terminal.

      IAC DONT DET

        The sender of this command REFUSES to send and receive subcommands
        to control the Data Entry Terminal.

      The DET option uses five classes of subcommands 1) to establish the
      requirements and capabilities of the application and the terminal, 2)
      to format the screen, and to control the 3) edit, 4) erasure, and 5)
      transmission functions. The subcommands that perform these functions
      are described below.

      The Network Virtual Data Entry Terminal (NVDET)

        The NVDET consists of a keyboard and a rectangular display. The
        keyboard is capable of generating all of the characters of the ASCII
        character set. In addition, the keyboard may possess a number of
        function keys which when pressed cause a FN subcommand to be sent.

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    Data Entry Terminal Option

        (Although most DET's will support one or more peripheral devices
        such as a paper tape reader or a printer, this option does not
        consider their support. Support of peripheral devices should be
        treated by a is a separate option).

        The screen of the data entry terminal is a rectangle M characters by
        N lines. The values of M and N are set by negotiating the Output
        Line Width and Output Page Size options, respectively. The next
        writing position (x,y) on the screen (where x is the character
        position and y is the position of the line on the screen) is
        indicated by a special display character called the cursor. The
        cursor may be moved to any position on the screen without disturbing
        any characters already on the screen. Cursor addressing in existing
        terminals utilizes several topologies and addressing methods. In
        order to make the burden of implementaton as easy as possible this
        protocol supports two topologies (the finite plane and the helical
        torus) and three addressing methods ((x,y); x and y, and relative
        increments). Since the finite plane with absolute addressing is the
        least ambiguous and the easiest to translate to and from the others,
        it is the default scheme used by the NVDET. The torodial form with
        either relative or absolute addressing is provided for convience.

        Also the NVDET provides a mechanism for defining on the screen
        fields with special attributes. For example, characters entered into
        these fields may be displayed with brighter intensity, highlighted
        by reverse video or blinking, or protected from modification by the
        user. This latter feature is one of the most heavily used for
        applications where the DET displays a form to be filled out by the
        user.

        The definition of the NVDET uses Telnet option subnegotiations to
        accomplish all of its functions. Since none of the ASCII characters
        sent in the data stream have been used to define these functions,
        the DET option can be used in a "raw" or even "rare" mode. In
        circumstances where the application program knows what kind of
        terminal is on the other end, it can send the ASCII characters
        required to control functions not supported by the option or an
        implementation. In general keeping all NVDET functions out of the
        data stream provides better flexibility.

      Facility Functions  (for detailed semantics see Section 5.)

        IAC SB DET <DET facility subcommand><facility map> IAC SE

        where <DET facility subcommand> is one 8-bit byte indicating  the
        class of the facilities to be described, and <facility map> is a
        field of one or two  8-bit  bytes containing  flags  describing  the

    John Day                                                        [page 2]

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    Data Entry Terminal Option

        facilities required or desired by the sender.  The bits of the
        facility maps are numbered from the right starting at zero.  Thus,
        if bit 2 is set the field will have a decimal  value  of  4.   The
        values of the field are as follows:

        facility cmd:  EDIT FACILITIES                    subcommand code: 1

          facility map:                              bit numbers

            Toroidal Cursor Addressing                  6
            Incremental Cursor Addressing               5
            Read Cursor Address                         4
            Line Insert/Delete                          3
            Char Insert/Delete                          2
            Back Tab                                    1
            Positive Addressing only                    0

        where:

        If the Toroidal Cursor Addressing bit is set, the sender requests or
        provides that the SKIP TO LINE and SKIP TO CHAR subcommands be
        supported.

        If the Incremental Cursor Addressing bit is set, the sender requests
        or provides that the UP, DOWN, LEFT, and RIGHT subcommands be
        supported.

        If the Read Cursor bit is set, the sender requests or provides the
        READ CURSOR subcommand.

        If the Line Insert/Delete bit is set, the sender requests or
        provides that the LINE INSERT and LINE DELETE subcommands be
        supported.

        If the Char Insert/Delete bit is set, the sender requests or
        provides that the CHAR INSERT and CHAR DELETE subcommands be
        supported.

        If the Back Tab bit is set, the sender requests or provides that the
        BACK TAB subcommand be supported.

        If the Positive Addressing bit is set, then the sender is informing
        the receiver that it can only move the cursor in the positive
        direction. (Note: Terminals that have this property also have a Home
        function to get back to the beginning.)

    John Day                                                        [page 3]

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        facility cmd:  ERASE FACILITIES                  subcommand code:  2

          facility map:                                bit numbers

            Erase Field                                     4
            Erase Line                                      3
            Erase Rest of Screen                            2
            Erase Rest of Line                              1
            Erase Rest of Field                             0

        where:

        If a bit of the facility map for this facility command is set, the
        sender requests or provides the facility indicated by the bit. For a
        more complete description of each of these functions see the Erase
        Functions section below.

        facility cmd:  TRANSMIT FACILITIES               subcommand code:  3

          facility map:                      bit numbers

            Data Transmit                         5
            Transmit Line                         4
            Transmit Field                        3
            Transmit Rest of Screen               2
            Transmit Rest of Line                 1
            Transmit Rest of Field                0

        where:

        If a bit of the facility map for this facility command is set, the
        sender requests or provides the facility indicated by the bit. For a
        more complete description of each of these functions see the
        Transmit Functions section below.

        facility cmd:  FORMAT FACILITIES                 subcommand code:  4

          facility map:                               bit numbers

            FN                                 byte 0      7
            Modified                                       6
            Light Pen                                      5
            Repeat                                         4
            Blinking                                       3
            Reverse Video                                  2
            Right Justification                            1
            Overstrike                                     0

    John Day                                                        [page 4]

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    Data Entry Terminal Option

            Protection On/Off                  byte 1      6
            Protection                                     5
            Alphabetic-only Protection                     4
            Numeric-only Protection                        3
            Intensity                                      0-2

        where:

        If the FN bit is set, the sender requests or provides the FN
        subcommand.

        If the Modified bit is set, the sender requests or provides the
        ability to indicate fields that are modified and supports the
        TRANSMIT MODIFIED subcommand.

        If the Light Pen bit is set, the sender requests or provides the
        support of a light pen, including the Pen Selectable attribute of
        the DATA FORMAT subcommand.

        If the Repeat bit is set the sender requests or provides the REPEAT
        subcommand.

        If the Blinking bit is set, the sender requests or provides the
        ability to highlight a string of characters by causing them to
        blink.

        If the Reverse Video bit is set, the sender requests or provides the
        ability to highlight a string of characters by "reversing the video
        image," i.e., if the characters are normally displayed as black
        characters on a white background, this is reversed to be white
        characters on a black background, or vice versa.

        If the Right Justification bit is set, the sender requests or
        provides the ability to cause entries of data to be right justified
        in the field.

        If the Overstrike bit is set, the sender requests or provides the
        ability to superimpose one character over another on the screen much
        like a hard copy terminal would do if the print mechanism struck the
        same position on the paper with different characters.

        If the Protection On/Off bit is set, the sender requests or provides
        the ability to turn on and off field protection.

        If the Protection bit is set, the sender requests or provides the
        ability to protect certain strings of

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    Data Entry Terminal Option

        characters displayed on the screen from being altered by the user of
        the terminal. Setting this bit also implies that ERASE UNPROTECTED,
        DATA TRANSMIT, FIELD SEPARATOR, and TRANSMIT UNPROTECTED subcommands
        (see below) are supported.

        If the Alphabetic-only Protection bit is set, the sender requests or
        provides the ability to constrain the user of the terminal such that
        he may only enter alphabetic data into certain areas of the screen.

        If the Numeric-only Protection bit is set, the sender requests or
        provides the ability to constrain the user of the terminal such that
        he may only enter numerical data into certain areas of the screen.

        The three bits of the Intensity field will contain a positive binary
        integer indicating the number of levels of intensity that the sender
        requests or provides for displaying the data. The value of the 3 bit
        field should be interpreted in the following way:

          1        one visible intensity
          2        two intensities; normal and bright
          3        three intensities; off, normal, and bright
          >3        >3 intensities; off, and the remaining levels
          proportioned from dimmest to brightest intensity.

        For the all of the above commands, if the appropriate bit in
        <facility map> is not set, then the sender does not request or
        provide that facility.

      Editing Functions

        IAC SB DET MOVE CURSOR <x><y> IAC SE              subcommand code: 5

        where <x> is an 8-bit byte containing a positive binary integer
        representing the character position of the cursor, <y> is an 8-bit
        byte containing a positive binary integer representing the line
        position of the cursor.

        This subcommand moves the cursor to the absolute screen address
        (x,y) with the following boundary conditions:

          if x>M-1, set x=M-1 and send an ERROR subcommand

          if y>N-1, set y=N-1 and send an ERROR subcommand

        This describes a finite plane topology on the screen.

    John Day                                                        [page 6]

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    Data Entry Terminal Option

        IAC SB DET SKIP TO LINE <y> IAC SE                subcommand code: 6

        where <y> is a positive 8-bit binary number.

        This subcommand moves the cursor to the absolute screen line y. x
        remains constant. For values of y>N-1

          y = y mod N.

        IAC SB DET SKIP TO CHAR <x> IAC SE                subcommand code: 7

        where <x> is a positive 8-bit binary number.

        This subcommand moves the cursor to the absolute character position
        x. y remains constant, unless x>M-1 in which case:

          x' = (x mod M)
          y' = (y+(x DIV N))
          where x' and y' are the new values of the cursor.

        These last two subcommands define a toroidal topology on the screen.

        IAC SB DET UP IAC SE                              subcommand code: 8

        IAC SB DET DOWN IAC SE                            subcommand code: 9

        IAC SB DET LEFT IAC SE                           subcommand code: 10

        IAC SB DET RIGHT IAC SE                          subcommand code: 11

        These subcommands are provided as a convenience for some terminals.
        The commands UP, DOWN, LEFT, and RIGHT are defined as

        UP:     (x,y)=(x, y-1 mod N)
        DOWN:   (x,y)=(x, y+1 mod N)
        LEFT:   (x,y)=(x-1, y); if x=0 then x-1 = 0

        RIGHT:  (x,y)=(x+1 mod M, y) and y = y+1 if x+1>M-1

        Note: DOWN, LEFT, and RIGHT cannot always be replaced by the ASCII
        codes for linefeed, backspace, and space respectively. The latter
        are format effectors while the former are cursor controls.

        IAC SB DET HOME IAC SE                           subcommand code: 12

        This subcommand positions the cursor to (0,0). This is equivalent to
        a MOVE CURSOR 0,0 or the sequence SKIP TO LINE 0, SKIP TO CHAR 0.

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    Data Entry Terminal Option

        This subcommand is provided for convenience, since most terminals
        have it as a separate control.

        IAC SB DET LINE INSERT IAC SE                    subcommand code: 13

        This subcommand inserts a line of spaces between lines y (the
        current line, determined by the position of the cursor) and line
        y-1. Lines y through N-2 move down one line, i.e. line y becomes
        line y+1; y+1 becomes y+2, ...; N-2 becomes N-1. Line N-1 is lost
        off the bottom of the screen. The position of the cursor remains
        unchanged.

        IAC SB DET LINE DELETE IAC SE                    subcommand code: 14

        This subcommand deletes line y where y is the current line position
        of the cursor. Lines y+1 through N-1 move up one line, i.e. line y+1
        becomes line y; y+2 becomes y+1; ...; N-1 becomes N-2. The N-1st
        line position is set to all spaces. The cursor position remains
        unchanged.

        IAC SB DET CHAR INSERT IAC SE                    subcommand code: 15

        This subcommand inserts the next character in the data stream
        between the xth and x-1st characters, where x is the current
        character position of the cursor. The xth through M-2nd characters
        on the line are shifted one character positon to the right. The new
        character is inserted at the vacated xth position. The M-1st
        character is lost. The position of the cursor remains unchanged.

        IAC SB DET CHAR DELETE IAC SE                    subcommand code: 16

        This subcommand deletes the character on the screen at the x-th
        position. The x-th character is removed and the characters x+1
        through M-1 are shifted one character position to the left to become
        the x-th through M-2nd characters. The M-1st character position is
        left empty. (For most terminals it will be set to a NUL or space.)
        The cursor position remains unchanged.

        IAC SB DET READ CURSOR IAC SE                    subcommand code: 17

        This subcommand requests the receiver to send the present position
        of the cursor to the sender.

        IAC SB DET CURSOR POSITION <x><y> IAC SE         subcommand code: 18

        where <x> and <y> are positive 8-bit binary integers.

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    Data Entry Terminal Option

        This subcommand is sent by a Telnet implementation in response to a
        READ CURSOR subcommand to convey the coordinates of the cursor to
        the other side. Note: x is less than M and y is less than N.

        IAC SB DET REVERSE TAB IAC SE                    subcommand code: 19

        This subcommand causes the cursor to move to the previous tab
        position. If none exists on the present line, the cursor moves to
        the previous line and so on until a tab is found or the address
        (0,0) is encountered. When field protection is in effect the cursor
        moves to the beginning of the preceding unprotected field.

      Transmit Functions (For detailed semantics see Section 5.)

        IAC SB DET TRANSMIT SCREEN IAC SE                subcommand code: 20

        This subcommand causes the terminal to transmit all characters on
        the screen from position (0,0) to (M-1,N-1). The cursor will be at
        (0,0) after the operation is complete.

        IAC SB DET TRANSMIT UNPROTECTED IAC SE           subcommand code: 21

        This subcommand causes the terminal to transmit all characters in
        unprotected fields from position (0,0) to (M-1,N-1). The unprotected
        fields are separated by the field separator subcommand. The cursor
        will be at (0,0) or at the beginning of the first unprotected field
        after the operation is complete.

        IAC SB DET TRANSMIT LINE IAC SE                  subcommand code: 22

        This subcommand causes the terminal to transmit all data on the yth
        line where y is determined by the present position of the cursor.
        Data is sent from character position (0,y) to the end-of-line or
        position (M-1,y) whichever comes first. The cursor position after
        the transmission is one character position after the end of line
        condition or the beginning of the next line, (0,y+1).

        IAC SB DET TRANSMIT FIELD IAC SE                 subcommand code: 23

        This subcommand causes the terminal to transmit all data in the
        field presently occupied by the cursor. The cursor position after
        the operation is complete is one character position after the end of
        the field or, if that

        position is protected, at the beginning of the next unprotected
        field.

    John Day                                                        [page 9]

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    Data Entry Terminal Option

        IAC SB DET TRANSMIT REST OF SCREEN IAC SE        subcommand code: 24

        This subcommand causes the terminal to transmit all characters on
        the screen from position (x,y) to (M-1,N-1) or until the end of
        text. (x,y) is the current cursor position. The cursor position
        after the operation is one character position after the last text
        character, or (0,0) if the last filled character position is
        (M-1,N-1).

        IAC SB DET TRANSMIT REST OF LINE IAC SE          subcommand code: 25

        This subcommand causes the terminal to transmit all characters on
        the yth line from position (x,y) to the end of line or (M-1,y)
        whichever comes first. (x,y) is the current cursor position. The
        cursor position after the operation is one character position after
        the last character of the line or the first character of the next
        line.

        IAC SB DET TRANSMIT REST OF FIELD IAC SE         subcommand code: 26

        This subcommand causes the receiver to transmit the rest of the
        characters in the field currently occupied by the cursor. The cursor
        position after the operation is at the beginning of the next field.

        IAC SB DET TRANSMIT MODIFIED IAC SE              subcommand code: 27

        This subcommand causes the receiver to transmit only those fields
        which have the modified attribute set. The cursor position after the
        operation is unchanged.

        IAC SB DET DATA TRANSMIT <x><y> IAC SE           subcommand code: 28

        This subcommand is used to preface data sent from the terminal in
        response to a user action or a TRANSMIT command. The parameters <x>
        and <y> indicate the initial position of the cursor. See the
        Transmit Subcommands subsection in Section 5 for more details. A
        DATA TRANSMIT subcommand may precede an entire transmission with
        each field being delineated by the FIELD SEPARATOR subcommand as
        would be the case in a response toa

        TRANSMIT UNPROTECTED. Or, it may precede each field as would be the
        case in a response to a TRANSMIT MODIFIED.

      Erase Functions

        IAC SB DET ERASE SCREEN IAC SE                   subcommand code: 29

    John Day                                                       [page 10]

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    Data Entry Terminal Option

        This subcommand causes all characters to be removed from the screen.
        All fields regardless of their attributes are deleted. The cursor
        position after the operation will be (0,0). Most terminals set the
        erased characters to either NUL or space characters.

        IAC SB DET ERASE LINE IAC SE                     subcommand code: 30

        This subcommand causes all characters on the yth line to be removed
        from the screen, where y is the line of the current cursor position.
        All fields regardless of their attributes are deleted. The cursor
        position after this operation will be (0,y). Note: This operation
        can be easily simulated by the sequence: LINE DELETE, LINE INSERT.
        However, the order is important to insure that no data is lost off
        the bottom of the screen.

        IAC SB DET ERASE FIELD IAC SE                    subcommand code: 31

        This subcommand causes all characters in the field occupied by the
        cursor to be removed. The cursor position after the operation is at
        the beginning of the field.

        IAC SB DET ERASE REST OF SCREEN IAC SE           subcommand code: 32

        This subcommand causes all characters from position (x,y) to
        (M-1,N-1) to be removed from the screen. All fields regardless of
        their attributes are deleted. The cursor position after the
        operation is unchanged. This is equivalent to doing an ERASE REST OF
        LINE plus a LINE DELETE for lines greater than y.

        IAC SB DET ERASE REST OF LINE IAC SE             subcommand code: 33

        This subcommand causes all characters from position (x,y) to (M-1,y)
        to be removed from the screen All fields regardless of their
        attributes are deleted. The cursor position after the operation is
        unchanged.

        IAC SB DET ERASE REST OF FIELD IAC SE            subcommand code: 34

        This subcommand causes all characters from position (x,y) to the end
        of the current field to be removed from the screen. The cursor
        position after the operation is unchanged.

        IAC SB DET ERASE UNPROTECTED IAC SE              subcommand code: 35

        This subcommand causes all characters on the screen in unprotected
        fields to be removed from the screen. The cursor position after the

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    Data Entry Terminal Option

        operation is at (0,0) or, if that position is protected, at the
        beginning of the first unprotected field.

      Format Functions

        IAC SB DET FORMAT DATA <format map><count> IAC SE
                                                         subcommand code: 36

        where <format map> is a two byte field containing the following
        flags:

          Byte 0
            Blinking                                 7
            Reverse Video                            6
            Right Justification                      5
            Protection                              3-4
            Intensity                               0-2
          Byte 1
            Modified                                1
            Pen Selectable                          0

        where:

        If the Blinking bit is set, the following field of <count>
        characters should have the Blinking attribute applied to it by the
        receiver.

        If the Reverse Video bit is set, the following field of <count>
        characters should be displayed by the receiver with video reversed.

        If the Right Justification bit is set, the input entered into the
        field of <count> characters should be right justified.

        The Protection field is two bits wide and may take on the

        following values:

          0         no protection
          1         protected
          2         alphabetic only
          3         numeric only

        The protection attribute specifies that the other side may modify
        any character (no protection), modify no characters (protected),
        enter only alphabetical characters (A-Z, and a-z) (alphabetic only),
        or enter only numerical characters (0-9,+,.,and -) (numeric only) in
        the following field of <count> bytes.

    John Day                                                       [page 12]

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        The Intensity field is 3 bits wide and should be interpreted in the
        following way:

          The values 0-6 should be used as an indication of the relative
          brightness to be used when displaying the characters in or entered
          into the following field <count> characters wide. The number of
          levels of brightness available should have been obtained
          previously by the Format Facility subcommand. The exact algorithm
          for mapping these values to the available levels of intensity is
          left to the implementors. A value of 7 in the intensity field
          indicates that the brightness should be off, and any characters in
          or entered into the field should not be displayed.

        If the Modified bit is set, the field is considered to have been
        modified and will be transmitted in response to a TRANSMIT MODIFIED
        subcommand.

        If the Pen Selectable bit is set, the field can be selected with the
        light pen. Note: Use of the light pen should be the subject of
        another Telnet option.

        <count> is 2 bytes that should be interpreted as a positive 16-bit
        binary integer representing the number of characters following this
        command which are affected by it.

        Data sent to the terminal or the Using Host for unwritten areas of
        the screen not in the scope of the count should be displayed with
        the default values of the format map. The default values are No
        Blinking, Normal Video, No Justification, No Protection and Normal
        Intensity. For example, suppose a FORMAT DATA subcommand was sent to
        the terminal with attributes Blinking and Protected and a

        count of 5 followed by the string "Name: John Doe". The string
        "Name:" would be protected and blinking, but the string "John Doe"
        would not be.

        This subcommand is used to format data to be displayed on the screen
        of the terminal. The <format map> describes the attributes that the
        field <count> bytes wide should have. This field is to start at the
        position of the cursor when the command is acted upon. The next
        <count> displayable characters in the data stream are used to fill
        the field. Subsequent REPEAT subcommands may be used to specify the
        contents of this field. If the sender specifies attributes that have
        not been agreed upon by the use of the Format Facility subcommand,
        the Telnet process should send an Error Subcommand to the sender,
        but format the screen as if the bit had not been set.

    John Day                                                       [page 13]

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        IAC SB DET REPEAT <count><char> IAC SE           subcommand code: 37

        where <count> is a positive 8-bit binary integer. <char> is an 8-bit
        byte containing an ASCII character.

        This subcommand is used to perform data compression on data being
        transferred to the terminal by encoding strings of identical
        characters as the character and a count. The repeated characters may
        be part of a field specified

        IAC SB DET SUPPRESS PROTECTION <negotiation> IAC SE
                                                         subcommand code: 38

        where <negotiation> may have the values of the Telnet option
        negotiation:

          251                 WILL
          252                 WONT
          253                 DO
          254                 DONT

        This subcommand is used to suppress the field protection in a
        non-destructive manner. Many data entry terminals provide the means
        by which protection may be turned on and off without modifying the
        contents of the screen or the terminal's memory. Thus, the
        protection may be turned off and back on without retransmitting the
        form.

        The default setting of the option is that protection is on, in other
        words

          IAC SB DET SUPPRESS PROTECTION WONT IAC SE
          IAC SB DET SUPPRESS PROTECTION DONT IAC SE

        Negotiation of this subcommand follows the same rules as
        negotiations of the Telnet options.

        IAC SB DET FIELD SEPARATOR IAC SE                subcommand code: 39

        It is necessary when transmitting only the unprotected portion of
        the screen to provide a means for delimiting the fields. Existing
        DET's use a variety of ASCII characters such as Tab, Group
        Separator, Unit Separator, etc. In order to maintain transparency of
        the NVDET this subcommand is used to separate the fields. Clearly,
        this incurs rather high overhead. This overhead can be avoided by
        using the Byte Macro Option (see Appendix 3).

    John Day                                                       [page 14]

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    Data Entry Terminal Option

      Miscellaneous Commands

        IAC SB DET FN <code> IAC SE                      subcommand code: 40

        where: <code> is one byte.

        Many data-entry terminals provide a set of "function" keys which
        when pressed send a one-character command to the server. This
        subcommand describes such a facility. The values of the <code> field
        are defined by the user and server. The option merely provides the
        means to transfer the information.

        IAC SB DET ERROR <cmd> <error code> IAC SE       subcommand code: 41

        where:

          <cmd> is a byte containing the subcommand code of the subcommand
          in error.

          <error code> is a byte containing an error code.

          (For a list of the defined error codes see Appendix 2.)

        This subcommand is provided to allow DET option implementations to
        report errors they detect to the corresponding Telnet process. At
        this point it is worth reiterating that the philosophy of this
        option is that when an error is detected it should be reported;
        however, the implementation should attempt its best effort to carry
        out the intent of the subcommand or data in error.

    John Day                                                       [page 15]

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    Data Entry Terminal Option

    3. Default and Minimal Implementation Specifications

      Default

        WON'T DET -- DON'T DET

        Neither host wishes to use the Data Entry Terminal option.

      Minimal Implementation

        DET EDIT FACILITIES
        DET ERASE FACILITIES
        DET TRANSMIT FACILITIES
        DET FORMAT FACILITIES
        DET MOVE CURSOR <x><y>
        DET HOME
        DET ERASE SCREEN
        DET TRANSMIT SCREEN
        DET FORMAT DATA
        DET ERROR <cmd> <error code>

        In the case of formatting the data, the minimal implementation
        should be able to support a low and high level of intensity and
        protection for all or no characters in a field. These functions,
        however, are not required.

        The minimal implementation also requires that the Output Line Width
        and Output Page Size Telnet options be supported.

    John Day                                                       [page 16]

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    Data Entry Terminal Option

    4. Motivation

      The Telnet protocol was originally designed to provide a means for
      scroll-mode terminals, such as the standard teletype, to communicate
      with processes through the network. This was suitable for the vast
      majority of terminals and users at that time. However, as use of the
      network has increased into other areas, especially areas where the
      network is considered to provide a production environment for other
      work, the desires and requirements of the user community have changed.
      Therefore, it is necessary to consider supporting facilities that were
      not initially supported. This Telnet option attempts to do that for
      applications that require data entry terminals.

      This option in effect defines the Network Virtual Data Entry Terminal.
      Although the description of this option is quite long, this does not
      imply that the Telnet protocol is a poor vehicle for this facility.
      Data Entry Terminals are rather complex and varied in their abilities.
      This option attempts to support both the minimal set of useful
      functions that are either common to all or can be easily simulated and
      the more sophisticated functions supplied in some terminals.

      Unlike most real data entry terminals where the terminal functions are
      encoded into one or more characters of the native character set, this
      option performs all such controls within the Telnet subnegotiation
      mechanism. This allows programs that are intimately familiar with the
      kind of terminal they are communicating with to send commands that may
      not be supported by either the option or the implementation. In other
      words, it is possible to operate in a "raw" or at least "rare" mode
      using as much of the option as necessary.

      Although many data entry terminals support a variety of peripheral
      devices such as printers, cassettes, etc. it is beyond the scope of
      this option to entertain such considerations. A separate option should
      be defined to handle this aspect of these devices.

    John Day                                                       [page 17]

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    5. Description

      General Notes

        All implementations of this option are required to support a certain
        minimal set of the subcommands for this option. Section 3 contains a
        complete list of the subcommands in this minimal set. In keeping
        with the Telnet protocol philosophy that an implementation should
        not have to be able to parse commands it does not implement, every
        subcommand of this option is either in the minimal set or is covered
        by one of the facility subcommands. An implementation must
        "negotiate" with its correspondent for permission to use subcommands
        not in the minimal set before using them. For details of this
        negotiation process see the section below on facility subcommands.

        Most data entry terminals are used in a half duplex mode. (Although
        most DET's on the market can be used either as data entry terminals
        or as standard interactive terminals, we are only concerned here
        with their use as DET's.) When this option is used, it is suggested
        that the following Telnet options be refused: Echo, Remote
        Controlled Transmission and Echoing, and Suppress Go-Ahead. However,
        this option could be used to support a simple full duplex CRT based
        application using the basic cursor control functions provided here.
        For these cases, one or more of the above list of options might be
        required. (Support of sophisticated interactive calligraphic
        applications is beyond the scope of this option and should be done
        by another option or the Network Graphics Protocol.)

        In RFC 728, it was noted that a synch sequence can cause undesired
        interactions between Telnet Control functions and the data stream. A
        synch sequence causes data but not control functions to be flushed.
        If a control function which has an effect on the data immediately
        following it is present in the data stream when a synch sequence
        occurs, the control function will have its effect not on the
        intended data but on the data immediately following the Data Mark.
        The following DET subcommands are susceptible to this pitfall:

          CHAR INSERT
          DATA TRANSMIT
          FORMAT DATA

        The undesired interactions are best avoided by the receiver

        of the synch sequence deleting these subcommands and all data
        associated with them before continuing to process the control
        functions. This implies that the Data Mark should not occur in the
        middle of the data associated with these subcommands.

    John Day                                                       [page 18]

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    Data Entry Terminal Option

      Facility Subcommands

        These four subcommands are used by the User and Server
        implementations to negotiate the subcommands and attributes of the
        terminal that may be utilized. This negotiation can be viewed as the
        terminal (User Host) indicating what facilities are provided and the
        Server Host (or application program) indicating what facilities are
        desired.

        When Sent: A Server Telnet implementation using the DET option must
        send a facility subcommand requesting the use of a particular
        subcommand or terminal attribute not in the minimal implementation
        before the first use of that subcommand or attribute. The User
        Telnet implementation should respond as quickly as possible with its
        reply. Neither the User nor Server are required to negotiate one
        subcommand at a time. Also, a Telnet implementation responding to a
        facility subcommand is not required to give permission only for that
        subcommand. It may send a format map indicating all facilities of
        that class which it supports. However, a Telnet implementation
        requesting facilities must send a facility subcommand before its
        first use of the subcommand regardless of whether earlier
        negotiations have indicated the facility is provided. The facility
        cannot be used until a corresponding facility subcommand has been
        received. There are no other constraints on when the facility
        subcommands may be sent. In particular, it is not necessary for an
        application to know at the beginning of a session all facilities
        that it will use.

        Action When Recieved: There are two possible actions that may be
        taken when a facility subcommand is received depending on whether
        the receiver is a requestor or a provider (User).

        Requestor: When a facility subcommand is received by a requestor and
        it is in the state of Waiting for a Reply, it should go into the
        state of Not Waiting. It should then take the facility map it had
        sent and form the logical intersection with the facility map
        received. (For the Intensity attribute, one should take the minimum
        of the number received and the number requested.) The result
        indicates the facilities successfully negotiated. Note: if

        the receiver is not in the Waiting for Reply state, then this is the
        provider case described next.

        Provider: When a facility subcommand is received, it should send a
        facility subcommand with a facility map of the facilities it
        provides as soon as possible. It should then determine what new

    John Day                                                       [page 19]

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        facilities it is providing for the Requestor by forming the logical
        intersection of the facility map received and the one sent.

        Note: Although in most cases the requestor will be the Server Host
        and the provider will be the User Host supporting the terminal, this
        distinction may not always be true.

      Transmit Subcommands

        There are two kinds of transmit subcommands: those used to request
        that data be sent to the requestor, and one to preface data sent to
        the requestor. The first kind allow the requestor to control when,
        from where and to some degree how much data is transmitted from the
        terminal. Their explanation is straightforward and may be found in
        Section 2.

        Data may be sent from the terminal as a result of two events: the
        user of the terminal caused the transmission or in response to a
        transmit subcommand. Some programs may wish to know from where on
        the screen the transmission began. (This is reasonable, since the
        terminal user may move the cursor around considerably before
        transmitting.) Other programs may not need such information. The
        DATA TRANSMIT subcommand is provided in case this function is
        needed. When used this subcommand prefaces data coming from the
        terminal. The parameters <x> and <y> give the screen coordinates of
        the beginning of the transmission. <x> must be less than or equal to
        M-1 and <y> must be less than or equal to N-1. It is assumed that
        all data between this DATA TRANSMIT and the next one starts at the
        coordinates given by the first subcommand and continues filling each
        line thereafter according to the constraints of the screen and the
        format effectors in the data. Thus an intelligent or sloppy
        user-host DET implementation (depending on your point of view) need
        only include a DATA TRANSMIT subcommand when the new starting point
        is different from the last ending point.

    John Day                                                       [page 20]

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    Data Entry Terminal Option

    6.  Sample Interaction

      The nomenclature of RFC 726 will be used to describe this example.  To
      quote that RFC:

        "S:"  is sent from serving host to using host.
        "U:"  is sent from using host to serving host.
        "T:"  is entered by the terminal user.
        "P:"  is printed on the terminal.

        Text surrounded by square brackets([]) is commentary. Text
        surrounded by angle brackets (<>) is to be taken as a single unit.
        E.g, carriage return is <cr>, and the decimal value 27 is
        represented <27>.

        We assume that the user has established the Telnet connection,
        logged on, and an application program has just been started either
        by the user directly or through a canned start up  procedure. The
        presentation on the page is meant to merely group entities together
        and does not imply the position of message boundaries. One should
        assume that any part of the dialogue may be sent as one or many
        messages. The first action of the program  or Telnet is to negotiate
        the DET option:

      S: <IAC><DO><DET>

      U: <IAC><WILL><DET>

      S:<IAC><DO><OUTPUT PAGE SIZE>              [First negotiate the screen
                                                 size.  In this case we are
                                                 asking the user the size of
                                                 the terminal.  This could
                                                 have been done before the
                                                 DET option was negotiated.]

      U:<IAC><WILL><NAOP>

      U:<IAC><SB><NAOP><DR><25><IAC><SE>

      S:<IAC><SB><NAOP><DS><0><IAC><SE>

      S:<IAC><DO><OUTPUT LINE WIDTH>

    John Day                                                       [page 21]

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    Data Entry Terminal Option

      U:<IAC><SB><NAOL><DR><80><IAC><SE>         [Defines the screen to be
                                                 25 lines by 80 characters.
                                                 The server may use this
                                                 information when formatting
                                                 the screen.]

      S:<IAC><SB><NAOL><DS><0><IAC><SE>

      S:<IAC><SB><DET><FORMAT FACILITIES>
      <Repeat><Protection, 3 Levels
      Intensity><IAC><SE>                        [Now set the terminal
                                                 attributes.]

      U:<IAC><SB><DET><FORMAT FACILITIES>
      <Repeat, Blinking><Protection, 3
      Levels Intensity><IAC><SE>

      S:<IAC><SB><DET><ERASE SCREEN><IAC><SE>    [Erase the screen and start
                                                 sending the form.]

        <IAC><SB><DET><FORMAT DATA>
        <Protection=1, Intensity=1><0>
        <5><IAC><SE>Name:

        <IAC><SB><DET><MOVE CURSOR><0><1><IAC><SE>

        <IAC><SB><DET><FORMAT DATA>
        <Protection=1, Intensity=1><0>
        <8><IAC><SE>Address:

        <IAC><SB><MOVE CURSOR><0><4><IAC><SE>

        <IAC><SB><DET><FORMAT DATA>
        <Protection=1, Intensity=1><0>
        <17><IAC><SE>Telephone number:

        <IAC><SB><DET><MOVE CURSOR><32><4><IAC><SE>

        <IAC><SB><DET><FORMAT DATA>
        <Protection=1, Intensity=1><0>
        <24><IAC><SE>Social Security Number:

        <IAC><SB><DET><FORMAT DATA>
        <Protection=1, Intensity=7>
        <0><11><IAC><SE>                         [Establish a field that
                                                 doesn't display what is
                                                 typed into it.]

    John Day                                                       [page 22]

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        <IAC><SB><DET><MOVE CURSOR><32><5><IAC><SE>

        <IAC><SB><DET><FORMAT FACILITIES>
        <Blinking><0><IAC><SE>                   [Get permission to use
                                                 Blinking Attribute.]

      U:<IAC><SB><DET><FORMAT FACILITIES>
      <Repeat, Blinking><Protection,
      3 Levels Intensity><IAC><SE>

      S:<IAC><SB><DET><FORMAT DATA>
      <Blinking=1, Protection=1,
      Intensity=1><0><29><IAC><SE>

        Your SSN will not be printed.

        <IAC><SB><DET><HOME><IAC><SE>
        <IAC><GA>

      The previous exchange has placed a form on the screen that looks like:

      Name:
      Address:
      Telephone Number:                       Social Security Number:
                                         "Your SSN will not be printed."

      where the quoted string is blinking.

      The terminal user is now free to fill in the form provided. He
      positions the cursor at the beginning of the first field (this usually
      is done by hitting the tab key) and begins typing. We do not show this
      interaction since it does not generate any interaction with the User
      Telnet program or the network. After the terminal user has completed
      filling in the form, he strikes the transmit key to send the
      unprotected part of the form, but first the User Telnet program
      negotiates the Byte Macro Option to condense the Field Separator
      subcommand:

      U:<IAC><DO><BM>                            [Negotiate Byte Macro
                                                 Option.]

      S:<IAC><WILL><BM>                          [Define decimal 166 to be
                                                 the Field Separator
                                                 subcommand (see Appendix
                                                 3)]

    John Day                                                       [page 23]

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      U:<IAC><SB><BM><DEFINE>
      <166><6><IAC SB DET FIELD
      SEPARATOR IAC SE><IAC><SE>

      S:<IAC><SB><BM><ACCEPT><166><IAC><SE>      [The server accepts the
                                                 macro.]

      U:<IAC><SB><DET><DATA TRANSMIT><0><6><IAC><SE>
      John Doe <166> 1515 Elm St., Urbana, Il 61801
      <166> 217-333-9999 <166> 123-45-6789 <166>

      S:<IAC><SB><DET><ERASE SCREEN><IAC><SE>
      Thank you.

      And so on.

    John Day                                                       [page 24]

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    Appendix 1 - Subcommands, opcodes and syntax

      1         EDIT FACILITIES      <Facilty map>
      2         ERASE FACILITIES     <Facility map>
      3         TRANSMIT FACILITIES  <Facility map>
      4         FORMAT FACILITIES    <Facility map 1> <Facility map 2>
      5         MOVE CURSOR          <x> <y>
      6         SKIP TO LINE         <y>
      7         SKIP TO CHAR         <x>
      8         UP
      9         DOWN
      10        LEFT
      11        RIGHT
      12        HOME
      13        LINE INSERT
      14        LINE DELETE
      15        CHAR INSERT
      16        CHAR DELETE
      17        READ CURSOR
      18        CURSOR POSITION      <x><y>
      19        REVERSE TAB
      20        TRANSMIT SCREEN
      21        TRANSMIT UNPROTECTED
      22        TRANSMIT LINE
      23        TRANSMIT FIELD
      24        TRANSMIT REST OF SCREEN
      25        TRANSMIT REST OF LINE
      26        TRANSMIT REST OF FIELD
      27        TRANSMIT MODIFIED
      28        DATA TRANSMIT <x><y>
      29        ERASE SCREEN
      30        ERASE LINE
      31        ERASE FIELD
      32        ERASE REST OF SCREEN
      33        ERASE REST OF LINE
      34        ERASE REST OF FIELD
      35        ERASE UNPROTECTED
      36        FORMAT DATA <format map>
      37        REPEAT     <count><char>
      38        SUPPRESS PROTECTION <negotiation>
      39        FIELD SEPARATOR
      40        FN <code>
      41        ERROR  <cmd><error code>

    John Day                                                       [page 25]

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    Appendix 2 - Error Codes

      1         Facility not previously negotiated.

      2         Illegal subcommand code.

      3         Cursor Address Out of Bounds.

      4         Undefined FN value.

      5         Can't negotiate acceptable line width.

      6         Can't negotiate acceptable page length.

      7         Illegal parameter in subcommand.

      8         Syntax error in parsing subcommand.

      9         Too many parameters in subcommand.

      10        Too few parameters in subcommand.

      11        Undefined parameter value

      12        Unsupported combination of Format Attributes

    John Day                                                       [page 26]

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    Appendix 3 - Use of the Byte Macro Option

      One of the major drawbacks of the DET option is that because the
      functions are encoded as Telnet option subnegotiations a fairly high
      overhead is incurred. A function like Character Insert which is
      encoded as a single byte in most terminals requires six bytes in the
      DET option. Originally the only other solution that would have
      accomplished the same transparency that the use of subcommands
      provides would have been to define additional Telnet control
      functions. However, since this would entail modification of the Telnet
      protocol itself, it was felt that this was not a wise solution. Since
      then the Telnet Byte Macro Option (RFC 729) has been defined. This
      option allows the user and server Telnets to map an arbitrary
      character string into a single byte which is then transferred over the
      net. Thus the Byte Macro Option provides the means for implementations
      to avoid the overhead for heavily used subcommands. The rest of this
      appendix suggests how the Byte Macro Option should be applied to the
      DET option.

      In keeping with the specification of the Byte Macro Option, macro
      bytes will be chosen from the range 128 to 239. For the DET option, it
      is suggested that macro bytes be chosen by adding the subcommand code
      to 128. In addition, an unofficial DET subcommand might be defined
      indicating that each side was willing to support macro bytes for all
      subcommands (but not necessarily support all of the subcommands
      themselves) according to this algorithm. This subcommand would be:

        IAC SB DET DET-MACRO <negotiation> IAC SE       subcommand code: 254

      where <negotiation> may have the values of the Telnet option
      negotiation:

        251     WILL
        252     WONT
        253     DO
        254     DONT

      This subcommand is sent by a Telnet implementation to indicate its
      willingness to adopt byte macros for all of the DET subcommands
      according to the following algorithm:

        The macro byte for subcommand i will be i+128 and will represent the
        following string for parameterless subcommands:

        IAC SB DET <subcommand code> IAC SE

        and the following string for subcommands with parameters:

    John Day                                                       [page 27]

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        IAC SB DET <subcommand code>

        The default setting for this subcommand is that the macros are not
        in effect, in other words,

          IAC SB DET DET-MACRO WONT IAC SE
          IAC SB DET DET-MACRO DONT IAC SE

        Negotiation of this subcommand follows the same rules as
        negotiations of the Telnet options.

    John Day                                                       [page 28]

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    Data Entry Terminal Option

    References

      1.   ADM-1 Interactive Display Terminal Operator's Handbook
           Lear-Siegler, Inc. 7410-31.

      2.   ADM-Interactive Display Terminal Operator's Handbook
           Lear-Siegler, Inc. EID, 1974.

      3.   Burroughs TD 700/800 Reference Manual, Burroughs Corp., 1973

      4.   Burroughs TD 820 Reference Manual, Burroughs Corp. 1975.

      5.   CC-40 Communications Station: General Information Manual.
           Computer Communication, Inc. Pub. No. MI-1100. 1974.

      6.   Crocker, David. "Telnet Byte Macro Option," RFC 729, 1977.

      7.   Data Entry Virtual Terminal Protocol for Euronet, DRAFT, 1977.

      8.   Day, John. "A Minor Pitfall in the Telnet Protocol," RFC 728,
           1977.

      9.   Hazeltine 2000 Desk Top Display Operating Instructions. Hazeltine
           IB-1866A, 1870.

      10.  How to Use the Consul 980: A Terminal Operator's Guide and
           Interface Manual. Applied Digital Data Systems, Inc. 98-3000.

      11.  How to Use the Consul 520: A Terminal Operator's Guide and
           Interface Manual. Applied Digital Data Systems, Inc. 52-3000.

      12.  Honeywell 7700 Series Visual Information Projection (VIP)
           Systems: Preliminary Edition. 1973.

      13.  An Introduction to the IBM 3270 Information Display System. IBM
           GA27-2739-4. 1973.

      14.  Naffah, N. "Protocole Appareil Virtuel type Ecran" Reseau
           Cyclades. TER 536. 1976.

      15.  Postel, Jon and Crocker, David. "Remote Controlled Transmission
           and Echoing Telnet Option", RFC 726 NIC 39237, Mar. 1977.

      16.  Schicker, Peter. "Virtual Terminal Protocol (Proposal 2). INWG
           Protocol Note #32., 1976.

    John Day                                                       [page 29]

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    Data Entry Terminal Option

      17.  UNISCOPE Display Terminal : Programmer Reference . Sperry- Univac
           UP-7807 Rev. 2, 1975.

      18.  Universal Terminal System 400: System Description. Sperry- Univac
           UP-8357, 1976.

      19.  Walden, David C. "Telnet Output Line Width Option." NIC # 20196,
           1973, also in ARPANET Protocol Handbook, 1976.

      20.  Walden, David C. "Telnet Output Page Size" NIC # 20197, 1973,
           also in ARPANET Protocol Handbook, 1976.

    John Day                                                       [page 30]