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rfc:rfc732

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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NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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

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NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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.)

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

  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]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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

John Day [page 5]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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.

John Day [page 7]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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.

John Day [page 8]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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

John Day [page 11]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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]

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

  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]

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

  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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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]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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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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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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]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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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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]

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

  <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]

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

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]

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

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]

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

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]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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]

NWG/RFC# 732 DAY 13-Sep-77 18:38 41762 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]

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