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On-line Networked Terminals

❶Support of sophisticated interactive calligraphic applications is beyond the scope of this option and should be done by another option or the Network Graphics Protocol. Wikimedia Commons has media related to Data terminals.

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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. The cursor position after the operation is at the beginning of the next field. See the Transmit Subcommands subsection in Section 5 for more details. 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. The cursor position after this operation will be 0,y. This operation can be easily simulated by the sequence: However, the order is important to insure that no data is lost off the bottom of the screen.

The cursor position after the operation is at the beginning of the field. The cursor position after the operation is unchanged. The cursor position after the operation is at 0,0 or, if that position is protected, at the beginning of the first unprotected field. The Protection field is two bits wide and may take on the following values: The Intensity field is 3 bits wide and should be interpreted in the following way: 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.

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. This subcommand is used to format data to be displayed on the screen of the terminal. This field is to start at the position of the cursor when the command is acted upon. 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.

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. 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. Clearly, this incurs rather high overhead. This overhead can be avoided by using the Byte Macro Option see Appendix 3. 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 option merely provides the means to transfer the information. 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. These functions, however, are not required. 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.

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.

A separate option should be defined to handle this aspect of these devices. 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: 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 , 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: This implies that the Data Mark should not occur in the middle of the data associated with these subcommands.

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. 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.

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.

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

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: 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. When used this subcommand prefaces data coming from the terminal. 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.

To quote that RFC: The first word processors used text to communicate the structure of the document, but later word processors operate in a graphical environment and provide a WYSIWYG simulation of the formatted output. Programs such as Telix and Minicom control a modem and the local terminal to let the user interact with remote servers. On the Internet , telnet and ssh work similarly.

In the simplest form, a text terminal is like a file. Writing to the file displays the text and reading from the file produces what the user enters. In unix-like operating systems, there are several character special files that correspond to available text terminals. For other operations, there are special escape sequences , control characters and termios functions that a program can use, most easily via a library such as ncurses.

For more complex operations, the programs can use terminal specific ioctl system calls. For an application, the simplest way to use a terminal is to simply write and read text strings to and from it sequentially.

The output text is scrolled, so that only the last several lines typically 24 are visible. Unix systems typically buffer the input text until the Enter key is pressed, so the application receives a ready string of text.

In this mode, the application need not know much about the terminal. For many interactive applications this is not sufficient. One of the common enhancements is command line editing assisted with such libraries as readline ; it also may give access to command history. This is very helpful for various interactive command line interpreters.

Even more advanced interactivity is provided with full-screen applications. Those applications completely control the screen layout; also they respond to key-pressing immediately. This mode is very useful for text editors , file managers and web browsers. In addition, such programs control the color and brightness of text on the screen, and decorate it with underline, blinking and special characters e.

To achieve all this, the application must deal not only with plain text strings, but also with control characters and escape sequences , which allow to move cursor to an arbitrary position, to clear portions of the screen, change colors and display special characters, and also respond to function keys.

The great problem here is that there are so many different terminals and terminal emulators , each with its own set of escape sequences. In order to overcome this, special libraries such as curses have been created, together with terminal description databases, such as Termcap and Terminfo.

Dumb terminals are those that can interpret a limited number of control codes CR , LF , etc. In this context dumb terminals are sometimes dubbed glass Teletypes , for they essentially have the same limited functionality as does a mechanical Teletype. This type of dumb terminal is still supported on modern Unix-like systems by setting the environment variable TERM to dumb.

Smart or intelligent terminals are those that also have the ability to process escape sequences, in particular the VT52 , VT or ANSI escape sequences. A graphical terminal can display images as well as text. Graphical terminals are divided into vector-mode terminals, and raster mode. A vector-mode display directly draws lines on the face of a cathode-ray tube under control of the host computer system. The lines are continuously formed, but since the speed of electronics is limited, the number of concurrent lines that can be displayed at one time is limited.

Vector-mode displays were historically important but are no longer used. Practically all modern graphic displays are raster-mode, descended from the picture scanning techniques used for television , in which the visual elements are a rectangular array of pixels. Since the raster image is only perceptible to the human eye as a whole for a very short time, the raster must be refreshed many times per second to give the appearance of a persistent display. The electronic demands of refreshing display memory meant that graphic terminals were developed much later than text terminals, and initially cost much more.

Most terminals today are graphical, that is, they can show images on the screen. The modern term for graphical terminal is " thin client ". The bandwidth needed depends on the protocol used, the resolution, and the color depth. Modern graphic terminals allow display of images in color, and of text in varying sizes, colors, and fonts type faces.

In the early s an industry consortium attempted to define a standard, AlphaWindows , that would allow a single CRT screen to implement multiple windows, each of which was to behave as a distinct terminal. Unfortunately like I2O this suffered from being run as a closed standard: Possibly because of this the standard disappeared without trace. A terminal emulator is a piece of software that emulates a text terminal. In the past, before the widespread use of local area networking and broadband internet access, many computers would use a serial access program to communicate with other computers via telephone line or serial device.

Dec Terminal was one of the first terminal programs for the popular Altair. The Win32 console on Windows does not emulate a physical terminal that supports escape sequences [8] [ dubious — discuss ] so SSH and Telnet programs for logging in textually to remote computers for Windows, including the Telnet program bundled with some versions of Windows, often incorporate their own code to process escape sequences.

The terminal emulators on most Unix-like systems, such as, for example, gnome-terminal , qterminal, xterm , terminal. Terminals can operate in various modes, relating to when they send input typed by the user on the keyboard to the receiving system whatever that may be:. Different computer operating systems require different degrees of mode support when terminals are used as computer terminals.

The POSIX terminal interface , as provided by Unix and POSIX-compliant operating systems, does not accommodate block-mode terminals at all, and only rarely requires the terminal itself to be in line-at-a-time mode, since the operating system is required to provide canonical input mode , where the terminal device driver in the operating system emulates local echo in the terminal, and performs line editing functions at the host end.

Most usually, and especially so that the host system can support non-canonical input mode , terminals for POSIX-compliant systems are always in character-at-a-time mode. From Wikipedia, the free encyclopedia. This article has multiple issues. Please help improve it or discuss these issues on the talk page.

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Based on OED, B. The History of a Pioneer Computer. The New York Times. Dictionary of Information Technology. UNIX systems for microcomputers.

Professional and industrial computing series. Mastering UNIX serial communications.

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The overall library data entry rate is limited to the number of available data entry terminals and operators. Automating with barcodes Other PSC products include a line of handheld and fixed-position bar code scanners, wireless portable data entry terminals and warehouse management software.

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A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying or printing data from, a computer or a computing system. The teletype was an example of an early day hardcopy terminal, [2] and predated the use of a computer screen by decades.

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See The circuit and PCB have been produced and tested and basic code is available on github. See the. A portable data terminal, or shortly PDT, is an electronic device that is used to enter or retrieve data via wireless transmission (WLAN or WWAN). They have also been called enterprise digital assistants (EDA), data capture mobile devices, .

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The Data Entry Terminal (DET) has not been tested by Varec under all possible operational conditions, and Varec may not have all the data re lative to your application. The information in this instruction manual is not all inclusive and does not and cannot take into account all unique. handheld data entry terminal used to program the various sentex telephone entry units with ribbon connecting cable.