VT36 Color Graphics Display Control System

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The VT36 Color Graphics Display Control System is based on the VSV11 Graphic System enhanced by a dedicated PDP-11 processor and a special high level Picture Definition Language. The full featured variant of the VT36 incorporates the VRV02 19" RGB Color Monitor and the H3060 Joystick.

VT36 Info Brochure

An intelligent, multiple display control system for PDP-11 and VAX computers.

The VT36 from Digital Equipment is a new approach to color display systems. Developed as a complete hardware and software package, the VT36 supersedes conventional display systems by performing all picture display tasks internally, leaving the user free to concentrate on the application. The powerful software of the VT36 also performs dynamic picture update - displaying changes in the process the user is monitoring as they occur. Being microprocessor-based, the VT36 minimises the processing load on the host computer. Up to four VT36s can, therefore, be configured on one host PDP-11 or VAX, and one VT36 can itself support up to four independent display stations (video controller and display monitor)."

Intelligent, stand-alone subsystem

The VT36 is a microprocessor-controlled sub-system which performs the display functions many color display systems leave to the host computer. Only high level communications are needed from the host, so the VT36 significantly reduces the load on the host CPU, freeing it for other processing.

A VT36 has memory space for up to eight different pictures. A picture can be built up, edited and stored on the VT36’s mass storage device (available as an option) without involving the host processor. Pictures can also be stored on host mass storage for subsequent retrieval.

Full color

Displaying data in color makes it easier for operators to absorb facts, recognize their significance and, hence, react quickly. The VT36 implements these benefits by displaying data in up to 16 discrete colors. A color monitor is available from Digital, for use with the VT36.

Mimics and graphics

The VT36 enables the user to represent data in pictorial forms, such as mimic displays and graphics. This maximizes the amount of data which can be communicated without the risks of ambiguity and misinterpretation.

The VT36 can provide vector graphics facilities, enabling the user to create highly complex pictures. 512X256 point resolution is standard; 512X512 resolution can be provided as an option. For mimics and semi-graphics, standard ASCII characters (upper/lower case alphabet, numerics, etc) and graphics symbols (triangles, squares, etc) are provided. These can be displayed on a 6X6, 8X6, 8X8 or 6X8 dot matrix. Alternatively, users can define their own characters and display them on a matrix of any size.

Easy picture construction

The VT36 software package is designed to enable the user to build up and edit pictures quickly and easily - both on-line and off-line. Typically, a user will draw, on squared paper, the picture to be created. The coordinates are then keyed in from the drawing, with simple commands from the VT36 high level Picture Definition Language; for example:

LINE 30, 10, BLUE

causes a blue line to be drawn from the current coordinate position to coordinates 30 and 10 on the X and Y axes.

A library of symbols and characters can be built up, and then incorporated into pictures at any position simply by inputting the symbol number and the starting coordinates.

On-line picture creation and modifications to existing pictures can be performed, through use of the VT36 keyboard, which has special keys for performing graphics functions, and the VT36 rate-type joystick.

Dynamic picture update

With the VT36, changes in the user’s data base can be communicated to the appropriate display screens as they occur. This is achieved with a very simple software interface between the user’s system and the component of the VT36 system software which resides in the host computer.

The user’s applications software simply sends a message to the host component of the VT36 system software which down-line loads it to any remote VT36 system displaying that variable. The message is then decoded and the appropriate changes made immediately, at the display stations showing the picture. As the VT36is an intelligent device, this process is performed automatically, without the intervention of the user.

Field-proven technology

The VT36 architecture is based on proven technology in the color graphics market. The system is fully supported and maintained by Digital on a world-wide basis.


By combining a powerful 16-bit microprocessor, dedicated to the control of the display, with sophisticated graphics software, the VT36 maximizes the speed and accuracy with which data can be communicated. The following examples are just a few of the many applications where the VT36 can optimize man-machine communication:

  • Industrial process monitoring and control
  • Traffic control
  • Simulator systems
  • Power and public utility network control.

The VT36 comprises a complete hardware and software package to create pictures and link them dynamically to areal time process.


For all the advantages of an intelligent display system, with minimal CPU load, the VT36 is configured as a microprocessor based remote system, connected to the host via a serial line. Up to four VT36 systems, with a total maximum of 10 display stations on one host PDP-11 or VAX, can be configured in this way.

For applications where high system throughput is not required, up to four VT36 controllers can be configured within a host PDP-11.

The video controller comprises three printed circuit boards - the Image Processor, Image Memory and Sync. Generator - which function in the following way:

  • The Image Processor fetches graphics instructions from the VT36 microprocessor (remote system only) using DMA transfers from the computer memory. It interprets these instructions and fills the Image Memory with the appropriate display data.
  • The Image Memory is a complete video frame buffer with 512X256 standard resolution. As an option, the addition of a second Image Memory board can give 512X512 resolution. The Image Memory stores an image, in digital form, of the picture being displayed on the monitor.
  • The Sync. Generator module scans the Image Memory and provides the digital-to-analog conversion for displaying the data on a monitor.

The VT36 is supplied with a joystick, making it easy for the user to reposition the cursor. To complete the system, Digital offers models with a nineteen inch color monitor (grey-scale options are also available).

VT36 models with a monitor also include a VT100-type keyboard, enabling the user to build up and edit pictures on-line. It contains keys which initiate graphics functions such as:

  • controlling the cursor position
  • setting colors
  • filling a rectangle or triangle with color
  • placing a character on the display
  • performing a line-drawing sequence
  • enabling joystick operation

Up to four keyboards and/or joysticks can be used with the VT36. One keyboard and joystick can control any display in the cluster.

The VT36 software comprises components resident on both the slave and the host processors (if the system is configured local to the host then all the software resides on the host).

The host software performs the functions of: disk storage of all picture information, such as complete pictures, characters, symbols and sub-pictures; and distribution of that information to each intelligent VT36.

Two versions of the host software are available for operation under the VAX/VMS or RSX-11M/M-PLUS operating systems. In addition, the host software contains all the information to interface to and control the dynamic picture update function described later.

Communications between tasks resident in the host computer and the VT36 processors in the system are handled by a communications component in the VT36 software, using a simple, half-duplex protocol along serial communications lines.

The slave software contains modules which perform picture display and editing, and enable dynamic picture update using information supplied by the host.

Dynamic Picture Update

A picture built up on the VT36 comprises background and foreground information. The background information is information which never changes, such as the positioning of pipe-lines and roads. Foreground information consists of areas which can be linked to a variable in the user’s data base; for example, the temperature of a liquid, or pressure in a pipe-line. These areas can be defined in a variety of ways: as numbers, text, graphs, histograms, ‘states’ (i.e. colors, blink, special symbols), etc. When the user wishes to load a new picture, the following sequence is performed:

  • The user inputs a request to view a picture, via the VT36 keyboard.
  • The picture is loaded from the host disk storage by means of the LOAD function in the host software (all communications between the host and slave processors are handled by the VT36 communications software).
  • Keeping a record of this picture information, the VT36 microprocessor uses the DISPATCH function in its software to load the information to the appropriate video controller in the VT36 system.
  • Simultaneously, a REFRESH file is dispatched from the host REFRESH library, to the VT36. This contains current information from the user’s data base on the state of the variables which form the foreground picture.
  • The DISPLAY INTERPRETER function in the VT36 software processes this foreground information and loads it to the appropriate display station.

Once the picture has been loaded to a display station, information on the variables being displayed is stored by the REFRESH function in the host. As these variables change in the user’s data base (in line with changes in the process, network, etc), the user software sends a message to the REFRESH function, containing new information pertaining to that variable.

The REFRESH function then handles distribution of the new information to all the VT36 video controllers displaying pictures containing that variable. In the VT36, the data is converted to a form suitable for display on the appropriate screen(s).

In summary, once foreground and background picture information has been loaded to the VT36, the host processor is no longer involved in the display process, leaving it free for other processing. The VT36 performs all storage of pictures being displayed; conversion of digital data into a form suitable for output on a display; loading of background and foreground picture information to the displays.

The operator can respond to the situation on the screen and interact with the system by inputting commands via the VT100-type keyboard and joystick. These commands are then fed back to the host computer software.

Picture Creation

The VT36 Picture Creation Software makes it easy to build up pictures, sub-pictures, characters, symbols, etc, both off-line and on-line.

Off-line Picture Creation

This process involves outlining a picture on squared paper, dividing it up into logical sections (e.g. areas of a plant, or stages of a process), and defining the X-Y coordinates of each picture element (a character or symbol, for instance). These coordinates are then input to the VT36, from any standard terminal, along with the simple, but powerful, commands from the VT36 high level Picture Definition Language, such as:

  • INIT = Initializes screen to a specified color.
  • MARK = Outputs a special character.
  • POLY = Pre-sets the colour of a specified rectangle or triangle on the picture.
  • LINE = Draws a line from one coordinate to another.
  • TEXT = Inserts text on the screen.

These instructions are compiled by the VT36 Picture Assembler Process for subsequent use. Sub-pictures and characters can be built and then incorporated into pictures, at any position, simply by using the MARK command, with coordinates and the library numbers of the characters. This significantly reduces the complexity of building up pictures containing large numbers of identical picture elements.

In addition, a Character Definition Language is available, allowing the user to define characters, and a Field Definition Language is available for definition of the foreground picture information necessary in the dynamic update process.

On-line Picture Creation

A picture can be interactively built up by means of the joystick and special function keyboard and the Picture Creation Program. This method is normally used for forming and modifying picture elements, such as characters and foreground picture information, i.e. for constructing relatively small picture elements and for defining foreground picture information.

The following sample program with screen output shows how simple commands from the VT36 Picture Definition Language are used to create pictures:

     MOVE        -10,-10
     LINE        10,10,,M                 ;DRAWS MEDIUM THICKNESS LINE
     MOVE        -10,10                   ;GOTO START OF NEXT LINE
     LINE        10,-10,,M                ;DRAW OTHER LINE
     MOVE        0,0                      ;GO BACK TO ENTRY POINT
     ENDSUB                               ;END OF SUBROUTINE
GO:  INIT        BLACK                    ;PICTURE FILE START
     CSET        1,CHRJIM,,6,14           ;ASSOCIATE A 6X14 CHARACTER SET FOR TEXT
                                          ;CLEAR SCREEN TO BLACK
     MOVE        60,460                   ;GO TO START OF A LINE
     LINE        180,460,RED              ;DRAW A NORMAL THICKNESS LINE
                                          ;PUTS RED TEXT ON SCREEN
     MOVE        60,400                   ;SET FOR NEXT LINE
     LINE        180,400,BLUE,M           ;DRAW BLUE MEDIUM THICKNESS LINE
                                          ;ANNOTATE IT ON SCREEN IN BLUE
     MOVE        60,340
     LINE        180,340,GREEN,T          ;DRAW GREEN THICK LINE
     TEXT        200,340,<THIS IS A GREEN THICK LINE>
                                          ;ANNOTATE THE LINE
     POLY        180,264,60,244,ORANGE    ;THIS IS RECTANGLE FILLING
     POLY        60,200,180,180,CYAN,U    ;THIS IS TRIANGLE FILLING
     MOVE        60,120
     LINE        180,120, PURPLE          ;DRAW LINE AND PUT IN 2 CROSSES
     SUB         90,120,CROSS,LGREEN      ;ONE LIGHT GREEN
     SUB         150,120,CROSS,LBLUE      ;THE OTHER LIGHT BLUE
     MOVE        60,80                    ;NOW PUT IN LINE WITH MARKS ON IT
     LINE        180,80,OCHRE
     MARK        100,80,2,18,LGREEN
     MARK        120,80
     MARK        140,80
                                          ;3 LIGHT GREEN MARKS FROM
                                          ;THE SPECIAL SET (NO. 2)
                                          ;CHARACTER 18 IN THAT SET

Hardware Components


  • VAX-11/PROVUE SPD 25.84 UPI S83
  • RSX-11/PROVUE SPD 14.33

External Links