Around the mid s most intelligent terminals, costing less than most dumb terminals would have a few years earlier, could provide enough user-friendly local editing of data and send the completed form to the main computer. Another of the motivations for development of the microprocessor was to simplify and reduce the electronics required in a terminal.
That also made it practicable to load several "personalities" into a single terminal, so a Qume QVT could emulate many popular terminals of the day, and so be sold into organizations that did not wish to make any software changes. Frequently emulated terminal types included:. For example, the VT , Heathkit H19 in ANSI mode, Televideo , Data General D, and Qume QVT terminals all followed the ANSI standard, yet differences might exist in codes from function keys , what character attributes were available, block-sending of fields within forms, "foreign" character facilities, and handling of printers connected to the back of the screen.
Most terminals were connected to minicomputers or mainframe computers and often had a green or amber screen. Typically terminals communicate with the computer via a serial port via a null modem cable, often using an EIA RS or RS or RS or a current loop serial interface. In fact, the instruction design for the Intel was originally conceived at Computer Terminal Corporation as the processor for the Datapoint The screen of a PC did not contain any character generation hardware; all video signals and video formatting were generated by the video display card in the PC, or in most graphics modes by the CPU and software.
An IBM PC monitor, whether it was the green monochrome display or the color display, was technically much more similar to an analog TV set without a tuner than to a terminal. With suitable software a PC could, however, emulate a terminal, and in that capacity it could be connected to a mainframe or minicomputer. Eventually microprocessor-based personal computers greatly reduced the market demand for conventional terminals. In the s especially, "thin clients" and X terminals have combined economical local processing power with central, shared computer facilities to retain some of the advantages of terminals over personal computers:.
Org Server software under Linux. Since the advent and subsequent popularization of the personal computer , few genuine hardware terminals are used to interface with computers today. Using the monitor and keyboard , modern operating systems like Linux and the BSD derivatives feature virtual consoles , which are mostly independent from the hardware used.
When using a graphical user interface or GUI like the X Window System , one's display is typically occupied by a collection of windows associated with various applications, rather than a single stream of text associated with a single process. In this case, one may use a terminal emulator application within the windowing environment.
This arrangement permits terminal-like interaction with the computer for running a command line interpreter , for example without the need for a physical terminal device; it can even allow the running of multiple terminal emulators on the same device.
A text terminal , or often just terminal sometimes text console is a serial computer interface for text entry and display. Information is presented as an array of pre-selected formed characters. When such devices use a video display such as a cathode-ray tube , they are called a " video display unit " or "visual display unit" VDU or "video display terminal" VDT.
The System console is a text terminal used to operate a computer. Modern computers have a built-in keyboard and display for the console. Some Unix-like operating systems such as Linux and FreeBSD have virtual consoles to provide several text terminals on a single computer. The fundamental type of application running on a text terminal is a command line interpreter or shell , which prompts for commands from the user and executes each command after a press of Enter.
This includes Unix shells and some interactive programming environments. In a shell, most of the commands are small applications themselves. Another important application type is that of the text editor. A text editor occupies the full area of display, displays one or more text documents, and allows the user to edit the documents.
The text editor has, for many uses, been replaced by the word processor , which usually provides rich formatting features that the text editor lacks. 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. 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. 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. 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.
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: 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. Terminals that have this property also have a Home function to get back to the beginning. 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. For a more complete description of each of these functions see the Transmit Functions section below. 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. 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 bit is set, the sender requests or provides the ability to protect certain strings of characters displayed on the screen from being altered by the user of the terminal. 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: This subcommand moves the cursor to the absolute screen address x,y with the following boundary conditions: This subcommand moves the cursor to the absolute screen line y.
This subcommand moves the cursor to the absolute character position x. These last two subcommands define a toroidal topology on the screen. The latter are format effectors while the former are cursor controls. Lines y through N-2 move down one line, i. Line N-1 is lost off the bottom of the screen. The position of the cursor remains unchanged. The N-1st line position is set to all spaces. The cursor position remains unchanged.
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 M-1st character position is left empty. For most terminals it will be set to a NUL or space. 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.
The cursor will be at 0,0 after the operation is complete. 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. 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 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.
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 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.
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.
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,  and predated the use of a computer screen by decades.
See downlwhopkd.cf 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, .
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.