GB2153636A - Computer communications - Google Patents

Abstract

A computer communications system between at least one computer (6) and other equipments (7 to 12) such as peripherals and/or terminals employs translation of digital signals at available interfaces (1) into signals suitable for transmission via coaxial cable (3). Such translation is via units (2) at each interface (1) and modulated RF signals are applied to the coaxial cable with sufficient carrier frequency separation to assure the desired one-to-one communication. <IMAGE>

Description

SPECIFICATION Computer communications The invention relates to provisions for communications between computers, including micro-computers, and peripheral equipment, including printers, terminals and visual display units.

It is envisaged that preferred embodiments of the invention will utilise standard interfaces, and we have specifically in mind the well-known RS 232 serial interface for operation at various baud rates of up to 19.2 KHz with its own inherent power supply.

Clearly, signals at the interface, whether as output therefrom or as input thereto, and whether on a unidirectional or on a bidirectional basis, must have a nature and form determined by the requirements of the interface. In general, we envisage translation or conversion of such signals into a different nature and form that is more readily and flexibly transmitted for communication purposes, and we particularly propose herein the provision of a signal suited to transmission over normal coaxial cable, specifically a RF preferably VHF modulated signal.

According to one aspect of that invention we particularly propose that conversion of signals between standard interface form and transmission form be achieved within an interface connector unit, one per interface involved for communication purposes.

Effectively, such units may be viewed as a kind of interface extender operative to receive and/or transmit signals in a form better suited to communication at least from the point of view of readily tapping off or into the communication medium at reasonable cost as applies to normal coaxial cable and using T-connectors.

Self-evidently, such a system will improve upon existing practices using cabling for one-to-one connection through data points of up to 6 lines; or using an expensive special cable ring as for so-called Local Area Network terminals which constrains connection to specific points in order to avoid standing wave problems and does not readily permit disconnection.

In addition to basic conversion, say between full duplex RS 232 information signals and VHF signals for the coaxial cable, connector units will provide for a number of communication channels over the same coaxial cable, say up to 16 or even 128 channels for a particular computer installation, so as to allow all desired or required one-to-one communications between equipment connected to the ring.

Such channel provision is readily achieved by frequency division multiplex techniques, say at 500 Hz intervals for baud rates of 19.2 Kz on up to 6 lines, and time division multiplex could be used for in-channel or line coding.

It is preferred that connector units hereof permit either or both directions of communication, at least inherently and further preferably with provision whereby they are specifically configurable by presetting to a particular type of communication, so that the same units may be used anywhere in any particular computer/peripherals installation.

Moreover, there is clear advantage in connector units that are of the same basic design and readily configurable, say by switches and/or breaking/making conductor paths and/or installation of ROMs or EPROMs, in order to match particular installations and/or manufacturers' utilisations of interfaces, say as to baud rate, parity, jumpers between interface pins not required for communication, pulse widths, channel number identification, etc.

Practical implementation of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagram of a computer installation; Figure 2 shows a connector hereof; and Figure 3 is a block diagram of basic functional components for a connector hereof.

In Figure 1, a main computer 6 has associated therewith a microcomputer 9, a line printer 7, another printer 8, visual display units 10, and other peripheral units 11 and 12, any of which could, for example, be inter-active terminals, and might be in a different room and/or on a different floor from the main computer 6.

The main computer 6 is shown with a typical complement of sixteen interfaces 1 that, for the purpose of this description, are taken as all being of similar RS 232 serial type. For the peripheral units 7 to 12 actually shown, only seven of the interfaces are required, each dedicated, as usual, to a different one of the peripheral units 7 to 12. It will be appreciated that, again as usual, each of the peripheral units 7 to 12 also has a similar interface 1.

Communication between the main computer 6 and the peripheral units is over a single coaxial cable 3 with suitable T-connectors at 4 and branches of coaxial cable extending from them to connector units 2 hereof plugged into the RS 232 interfaces 1.

Suitable coaxial cable terminations are indicated at 5, so that the cable 3 effectively forms a common communication medium if not actually connected as a ring.

The connector units 2 will operate as aforesaid, i.e. converting between RS 232 interface signals and modulated RF signals for the coaxial cable 3 in accordance with system requirements. Those units 2 are shown in Figure 2 as basically comprising a 6-way D-type RS 232 interface plug 22 associated with a module 20 incorporating all necessary electronics and itself associated with a length coaxial cable 23. It will be understood that the D-type plug, the shape of the module 20, whether or not the coaxial cable cooperates with a plug/socket connection, and the nature of assembly together of those components is a matter entirely of choice and specific design preference. In addition, Figure 2 shows the electronics module 20 with configuration switches 21 of slider type, and, again, such provision and its nature is a matter of choice.If provided, such switches can determine channel numbers and prescribed operation modes, though such could well be provided automatically via connector unit electronics.

Turning now to the outline block diagram of Figure 3, one type of organisation of the electronics of module 20 is indicated for a basis of operation using frequency division multiplex for channel separation and identification and time division multiplex for in-channel or line coding.

Thus, a digital frequency synthesizer 30 is shown together with control circuitry 31, which may readily be implemented as a microprocessor and associated program ROM chip or chips; an RF modulator 32 with associated coding logic 33 making up a transmission section 37; and an RF demodulator 34 and associated decoding logic 35 making up a receiving section 38. The transmission and receiving sections 37 and 38 will share the control section 36 made up of frequency synthesizer 30 and control circuitry 31 for the purposes of determining at least normal main computer-to-peripheral unit channel (carrier frequency), transmit or receive mode, and time division multiplex (pulse width) coding/decoding of the RF signal for or from the coaxial ring 3.

Using a microcomputer as one peripheral and/or using active, so-called "intelligent", terminals there can often be a requirement for peripherals to be effectively in direct communication, normally, of course, controlled and effected via the main computer and its own interfaces. Using connector units hereof, however, and should the overall computer system so permit, direct one-to-one communications are feasible between the peripheral units.

In showing sixteen interfaces for the main computer 6, a typical small computer system is assumed, though it will be evident from previous mention of a 500 Hz channel separation and a baud rate of up to 19.2 KHz that larger systems up to 128 channels could be accommodated. There could, however, be advantages arising from simplification of RF circuitry of the connector units if restriction is made to sixteen channels, and sixteen will often be a convenient number for sub-groups of main computer and peripheral units intercommunication. Accordingly, it is envisaged that subgrouping of up to 128 fully bidirectional main computer interfaces will often be acceptable, perhaps especially with the evident options inherent herein for switching over of particular channels from one sub-group to another.

Overall, in the above, it will be noted that the electronics of our connector units utilises power supplied via the interface concerned, i.e. as applies to at least RS 232 interfaces. Moreover, the connector units hereof do not need to employ prior Local Area Network and/or synchronous packet switching techniques, with consequent increased flexibility and reduced costs.

It should be evident that the invention is applicable to interfaces other than RS 232, for example other serial interfaces with their own power source, such as RS 423 and RS 424.

Another feature of note is that failure of any one communication channel will not affect other communication channels pending repair.

Units with electronics as indicated in Figure 3 further offer the possibility of extension to serve as signal separators or repeaters within the communication ring.

Claims (7)

1. Computer communications system wherein at least one computer is connected between other equipments such as peripheral units and/or terminals via digital interfaces thereof and using coaxial cable for transmission purposes together with means for translation signals between digital formats of said interfaces and modulated RF format for said coaxial cable.

2. Computer communications system according to claim 1, comprising interface connector units each including electronic circuitry for said translation of signals and each being associated with a different said interface both at said computer at said other equipments.

3. Computer communications system according to claim 2, wherein said circuitry and units each include means for configuring to particular types of communication, whether one way or bidirectional.

4. Computer communications system according to claim 2 or claim 3, comprising an appropriately terminated main run of coaxial cable and T-connectors for branches of coaxial cable to each said unit.

5. Computer communications system according to any one of claims 2 to 4, wherein said circuitry include frequency division multiplex means whereby appropriate separated frequencies are assigned for desired one-to-one communications to and from particular said other equipments.

6. Computer communications system according to claim 5, wherein said separation is about 500 Hz.

7. Computer communications system substantially as herein described with reference to and as shown in the accompanying drawings.