This appendix offers a reference guide to Digital's earlier video terminals that have been replaced by new products.
The VT52 is an upper- and lowercase ASCII video terminal whose display holds 24 lines of 80 characters. The terminal features multikey rollover and keyclick.
The VT52 provides a two-way numeric keypad. In one mode, the keypad is used to generate program-compatible numeric codes. If your application requires much numeric input, you can use the VT52 without modifying hardware or software; or software can place the VT52 in the alternate mode, in which each key on the keypad transmits a unique escape sequence. This allows the host computer to distinguish between keys typed on the auxiliary keypad and similar keys on the main keyboard. In this mode, each key on the keypad can be used to invoke a user-defined function.
The VT52 has a wide range of cursor-positioning functions. As well as moving the cursor one position in any direction, software can move the cursor to any position on the screen with a Direct Cursor Addressing command that specifies the destination of the cursor. The VT52 also offers fixed horizontal tabs, a Cursor-to-Home command, and two screen-erasure functions. Data on the screen scrolls up when a linefeed function is performed with the cursor on the bottom line. Data scrolls down when a reverse linefeed function is performed with the cursor on the top line.
The VT55 is an on-line interactive video terminal. It serves as an alphanumeric, graph drawing, and printer/plotter terminal. It can be used in plotting histograms, waveform and peak analyses, data acquisition, monitoring, trending, simulation, and laboratory charts and forms. The VT55 allows simultaneous display of any combination of text and graphics, and supplies a hardcopy reproduction of the display screen for characters and graphs.
The VT55 can be used as a 24-line programmer's terminal, using only alphanumeric capability with the console keyboard and keypad. The VT55 is packaged in a compact desktop cabinet, and information is displayed on a 12-inch CRT.
The copier option uses a scanning technique similar to methods used in facsimile picture transmission systems. This technique, in conjunction with the use of modern recording paper, generates high-quality copy in a small package with a minimum of moving parts.
For most applications, the VT55 will be interfaced to a host computer with a serial line cable and operated in full-duplex communication mode. Data transmitted by the VT55 is received by the host computer. Data received by the VT55 is determined solely by the host computer.
The VT55 may also be set to local mode or to full-duplex with local copy mode of operation. The latter is useful when the host computer does not generate an immediate echo or response to a keyboard transmission, and a visual verification of the information being sent is desired.
The VT55 is capable of sending and receiving at rates from 75 to 9600 bits per second. Data is sent in serial digital format for the 20mA interface models. The EIA interface models allow the use of the VT55 with RS232-C signals.
VT55 models with Mate-N-Lok connectors are primarily intended for interfacing with 20mA digital serial line communications interfaces. Units with RS232-C connectors are compatible with RS232-C Standard Data Phone and modem connectors. Connector 283B is a telephone-type plug compatible with DECsystem-10s.