GB2149628A

GB2149628A - Visual data display system

Info

Publication number: GB2149628A
Application number: GB08426843A
Authority: GB
Inventors: Raymond Blakey; Michael Baker; Michael Gooday
Original assignee: LONDON REGIONAL TRANSPORT; TERMINAL DISPLAY SYSTEMS Ltd
Current assignee: LONDON REGIONAL TRANSPORT; TERMINAL DISPLAY SYSTEMS Ltd
Priority date: 1983-10-24
Filing date: 1984-10-24
Publication date: 1985-06-12
Also published as: GB8328349D0; GB8426843D0

Abstract

A visual data display system operates on two channels and includes two non-identical microprocessors (1,2) in the respective channels. Each processor is connected to a databus system (3) via a respective node (4, 5) and is arranged to transmit character signals serially to a dual input character generator (9). The character generator alternately supplies to a colour VDU (10), character signals indicative of the data in each channel so that any non-identity between the data received by the VDU (10) from the two channels and indicating non-reliable data is presented as a flashing character on the screen of the VDU (10). The inputs to the character generator are preferably switched once every second. The system is described for use in a railway "safety signaling" system. <IMAGE>

Description

SPECIFICATION Visual data display system This invention relates to a visual data display system and apparatus therefor and particularly to such a system and apparatus in which high reliability diagrams are displayed on a visual colour display device to provide information relating to operating conditions in a railway signalling system.

The basis of railway signalling provided on the Underground system of London Transport is known as 'safety signalling', i.e. the mechanisms operating sets of points and signals controlling trains over conflicting routes, are interlocked to prevent potentially hazardous conditions occurring.

At present, if a controlled signal remains at danger due to equipment failure, the only way a train may be routed past the signal, is to physically secure the points on the ground in the required path of the train.

An object of the present invention is to provide a system whereby the securing of points can be performed remotely in response to commands from a central control location. Such a system requires special signalling and computer equipment including a remote securing command computer with its own node, signal post telephones at all signals with remote securing and train radio and high reliability diagrams on visual display devices.

A particular object of the present invention is to provide a visual data display system including devices for displaying such high reliability diagrams.

At present visual display systems with visual display units illustrating colour diagrams and used in London Transport control rooms are single channel devices. That is to say that a change or condition of state at any signalling site produces a single message on a data bus for the diagram system, which then produces a single change in characters on the screen of a VDU.

In order to achieve high reliability and dependability with the diagrams produced on the screens of VDU's in a central control room, it is proposed in the present invention to employ a dual channel system.

Thus, according to one aspect of the present invention there is provided a visual data display system operating on two channels and including two non-identical microprocessors in the respective channels, each connected to a databus system via a respective node and each arranged to transmit character signals serially to a common character generator arranged to alternately supply to a visual colour display device character signals indicative of the data in each channel, any non-identity between the data received by the visual display device from two consecutive channels and indicating non-reliable data, being presented as a flashing character on the screen of the visual display device.

In one embodiment of the invention the system includes two diagram generator host computers each connected to the data bus system by a respective node. To ensure high integrity and reliability, each diagram computer should be individual in character and preferably produced by different manufacturers with software written by completely different authors. The data output from each computer is in the form of character codes transmitted serially to a character generator which will alternate the resultant data displays for each channel.

The invention will now be described by way of example only with particular reference to the accompanying drawings wherein: Figure 1 is a block diagram of the visual data display system of the present invention; Figure 2 is a block diagram of the character generator used in the system of the present invention and Figure 3 illustrates the diagrams produced alternatively on each channel on the VDU of the system of the invention.

Referring to Figure 1, the system consists of two diagram generator host microprocessors 1, 2, each connected to the data bus system line 3 via a respective node 4, 5, the processors 1, 2 receiving data from respective site computers via the respective nodes 4, 5 and also from keyboards 6, 7 respectively. A regulator keyboard 8 has has the input and output connected to both processors.

A dual input character generator 9 receives data signals from the processors 1, 2, and outputs signals to the colour VDU 10 on the output lines marked (RED), (GREEN) and (BLUE).

The data output from each processor is in the form of character codes transmitted serially to the dual input character generator 9 which is arranged to alternate the resultant data displays from each channel. For 1 second, channel 1 or page 1 will be displayed on the screen of VDU 10, and for alternate 1 second periods channel 2 or page 2 will be displayed.

Referring to Figure 2, which is a block diagram of the character generator 9, the arrangement once programmed into the generator, is completely fixed and held in firmware within a read only memory ROM.

The outputs from each last processor unit 1, 2, are transmitted to respective buffers 11, 12, via UART's 13, 14, interrupt level circuits 15, 16, and via main level circuits 17, 18 into completely separate picture memories 19, 20 which store pages 1 and 2 for the visual display unit 10. Outputs from the picture memories 19, 20 are connected via the contacts of switch 21, to a frame interrupt level unit 22; the switch operating every one second such that the screen data which originated from the processors 1, 2, is passed to the screen memory 23 alternately; the screen memory 23 being loaded with screen data originating from processor 1 for 1 second and for alternate 1 second periods, data originating from processor 2 is loaded into screen memory 23 such that the picture display unit 10 alternates between the two channels every second.

A further switch 24 couples the alternate outputs from screen memory 23 to the colour set 25 for page 1 of the display and to the colour set 26 for page 2 of the display, the outputs from colour sets 25 and 26 being transmitted via a character gener ator 27, and via red, blue and green channels to a colour monitor 28 of the colour VDU 10. Switch 24, is also connected via main level circuit 29 and respective interrupt level circuits 30, 31, to UART circuits 13, 14.

Any discrepancies in the picture data between channels will be indicated on the screen of the VDU 10 as a flashing character, indicating that there is non-identity between the data on the two channels and that the display information cannot be relied upon. In practice, an indication on the screen will only be accepted as correct and reliable provided that the 'diagram correct' indicators shown in Figure 3 are operating and that the indication on the screen gives a steady display for at least 4 seconds.

Referring to Figure 3, alternate black and white blocks 32 are provided in the four corners of the screen of the VDU and which verify that the displayed channel alteration has taken place by appropriate illumination of the blocks.

A cruciform shaped indicator 33 is provided in the left-hand top corner of the screen to indicate to the operator that the red, green and blue monitor channels are operating correctly.

Referring to the display on the VDU 10, page 1 is stored as normal video, i.e. normal foreground/ background colours and page 2 is stored as reverse video, i.e. foreground1background colours reversed. For the colour sets 19 and 20 (Figure 2), the colour set for page 1 will be in normal video whilst the colour set for page 2 will be in reverse video. Thus, in practice, if the wrong display character is supplied to the VDU screen within the wrong display period, then a character in reverse video will be displayed on the screen.

The link between the processors 1, 2, and the character generator 9, is a standard data link.

Either processor 1, 2, is able to command the character generator 9 to dump the entire screen display contents back to itself to verify the display data that it has transmitted. The character generator firmware will be arranged such that only the display data corresponding to the correct processor may be verified.

The video signal output from the character generator 9 to the colour monitor of the VDU 10 is a standard video signal.

The character generator is capable of displaying the standard 64 upper case ASC 11 character set, and is capable of displaying at least 95 special symbol characters in a matrix of 12 half dots wide by 9 dots high, in accordance with predetermined requirements. Of these 95 characters, at least 20 are 'safety characters' for each of which a different code is produced by each processor to produce the same character on the screen. This prevents the wrong character from appearing on the screen within the wrong display period as previously discussed.

It will be appreciated that the invention is capable of considerable modification and is not to be deemed limited to the particular features described and shown by way of example in the drawings.

Claims

1. A visual data display system operating on two channels and including two non-identical microprocessors in the respective channels, each connected to a databus system via a respective node and each arranged to transmit character signals serially to a common character generator arranged to alternately supply to a visual colour display device character signals indicative of the data in each channel, any non-identity between the data received by the visual display device from two consecutive channels and indicating non-reliable data, being presented as flashing character on the screen of the visual display device.

2. A visual data display system as claimed in Claim 1 wherein each microprocessor consists of a di character generator which outputs signals to a colour VDU and is arranged to alternate the resultant data displays from each channel or page of the VDU.

3. A visual data display system as claimed in Claim 2 wherein the outputs from each computer are transmitted via respective buffers into separate picture memories which store pages for the VDU, the outputs from the picture memories being connected via switching means to a frame interrupt level unit, the switching means operating continuously and switching at regular intervals of time such that for each time period, data originating from the two computers is passed to the screen memory of the VDU, alternately.

4. A visual data display system as claimed in Claim 3 including further switching means arranged to couple alternate outputs from said screen memory to a first colour set for a first page of the display and to a search colour set for a second page of the display, the outputs from the two colour sets being transmitted via a further character generator and via colour coded channels to a colour monitor of the colour VDU.

5. A visual data display system substantially as hereinbefore described and as shown in the accompanying drawings.