Telnet Data Entry Terminal option(1)

　　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

　　TelnetData 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.

　　(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 IAC SE

　　where is one 8-bit byte indicating the　class of the facilities to be described, and is a　field of one or two 8-bit bytes containing flags describing the 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: