GB2073407A

GB2073407A - Data communication system

Info

Publication number: GB2073407A
Application number: GB8010317A
Authority: GB
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1980-03-27
Filing date: 1980-03-27
Publication date: 1981-10-14
Also published as: DE3012105A1

Abstract

A data communications system comprising a plurality of stations; a first fiber optic transmission circuit connecting the stations in a loop configuration and enabling optical data to be transmitted to the stations around the loop in a first direction; a second fiber optic transmission circuit connecting the stations in a loop configuration and enabling optical data to be transmitted to the stations around the loop in a second direction opposite to the first; and each of the stations comprising a first transmitter/receiver connected to the first transmission circuit and a second transmitter/receiver connected to the second transmission circuit. <IMAGE>

Description

SPECIFICATION Data communication system This invention relates to data communications systems.

According to the invention, there is provided a data communications system comprising a plurality of stations; a first fiber optic transmission circuit connecting the stations in a loop configuration and enabling optical data to be transmitted to the stations around the loop in a first direction; a second fiber optic transmission circuit connecting the stations in a loop configuration and enabling optical data to be transmitted to the stations around the loop in a second direction opposite to the first; each of the stations comprising a first transmitter/receiver connected to the first transmission circuit and a second transmitter/receiver connected to the second transmission circuit.

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic drawing showing a bidirectional optical data transmission system according to the invention; Figure 2 shows diagrammatically the two transceivers used in each of the stations shown in Fig. 1; Figure 3 shows the details of the two transceivers for the central processing unit (CPU) of Fig. 1; and Figure 4 shows the details of the two transceivers for the data gathering unit (DGP) of Fig. 1.

Referring to Fig. 1, Central Processing Unit (CPU) 11 is connected to a plurality of data gathering panels (DGP) 12, 13 and 14 by alpha optical fiber loop 1 5 and beta optical fiber loop 1 6. Although CPUs and DGPs are shown, it is to be understood that the invention can be used in other types of communication sytems such as distributed processing systems. The alpha optical fiber loop 1 5 is comprised of a plurality of segments 17, 18, 1 9 and 20 which interconnect CPU 11 and DGPs 12, 13 and 14 in a series loop for transmitting data in a first direction shown by the arrows. Second optical loop 1 6 interconnects CPU 11 and DGPs 12, 13 and 14 in a second direction using segments 24, 25, 26 and 27.

The central processing unit and data gathering panels of the Alpha/Delta 1000 System manufactured by Honeywell, Inc. can be used for CPU 11 and DGPs 12, 13 and 14 with the addition of the transceivers shown in Figs.

3 and 4. The terminals shown in Figs. 3 and 4 show how these transceivers are connected to the corresponding terminals of the Alpha/ Delta 1000. In the four-wire loop mode, the Alpha/Delta 1000 CPU transmits and receives alternately on the alpha and beta loops.

No special modification of the Alpha/Delta 1000 hardware is necessary to accommodate the present fiber optic transmission system as long as the disclosed invention is used in conjunction therewith. Thus, the need for extensive fault detecting circuitry at the remote station is eliminated. Moreover the CPU will attempt to communicate with the station on one loop and, if it fails, will switch loops and attempt to communicate with the data gathering panel on the second loop.

The transceiver at the CPU and each DGP essentially comprises two transceivers such as 31 and 32 shown in Fig. 2. Transceiver 31 is connected to the alpha loop as shown and has a transmitter section 33 having an input for receiving the data from its associated station to be transmitted on the loop and an output connected to the loop over which this data is to be transmitted. Transceiver 31 also has a receiver section 34 having an input for receiving data from the alpha loop and an output for supplying this data to the station to which it is connected. Likewise, transceiver 32 is connected to the beta loop as shown. This transceiver has a transmitter section 35 having an input for receiving data from this station and an output connected to the beta loop over which this data is to be transmitted.

Transceiver 32 also has a receiver portion 36 having an input for receiving data from the beta loop and an output for supplying this data to its associated station.

Since transceivers 31 and 32 are slightly different depending on whether they are to be used in conjunction with CPU 11 or DGPs 12, 1 3 and 14, they have been set out separately in Figs. 3 and 4. When the station is a CPU the transceivers of Fig. 3 are used, and comprise a first receiver 41 having a receiver section 42 and a transmitter section 43 and a second transceiver 44 having a receiver section 45 and a transmitter section 46.

Photoresponsive 51 is optically coupled to the incoming alpha optical segment associated with the station in which transceiver 41 is being used and has a collector connected to a supply source and an emitter connected to a supply source through resistor 52, to ground through resistor 53 and to the negative input of amplifier 54. The positive input of amplifier 54 is connected to a source of supply through resistor 55 and to ground through variable resistor 56. Feedback resistor 57 connects the output of the amplifier back to its negative input. The output of amplifier 54 is connected through resistor 58 to the base of transistor 59 which has a collector connected to a source of positive potential through resistor 60 and an emitter connected directly ta ground.The junction of the collector of transistor 59 and resistor 60 is connected to the base of transistor 61 through resistor 62.

Transistor 61 has its collector connected to a source of positive potential through resistor 63 and its emitter connected directly to ground. The junction of resistor 63 and the collector of transistor 61 then provides the output from the receiver 42 and is connected to the TB 1-1 input of the central processing unit to which transceiver 41 is associated.

Optical isolators are used for connecting the transceivers to and from the stations shown in Fig. 1. These optical isolators can be represented by a diode such as shown in phantom in Fig. 3. The importance of diode 65 will become apparent hereinafter.

Transmitter 43 has essentially three inputs.

The first input is from the junction of the collector of transistor 59 and resistor 62 through the forward junction of diode 66 to the base of transistor 67. The second. input is from the line TB1-4 from the central processing unit to which this transceiver is associated to the junction of diode 66 and the base of transistor 67. The third input is from input line A-O to the base of transistor 75 through resistor 74. Transistor 67 has its base connected to ground through resistor 68, its collector connected to a source of positive potential through resistor 69 and its emitter connected directly to ground. The junction of resistor 69 and the collector of transistor 67 is connected through resistor 70 to the base of transistor 71 which has an emitter connected directly to ground and its collector connected through light emitting diode 72 and resistor 73 to a source of positive potential.Diode 72 is coupled to the outgoing alpha segment.

The collector of transistor 75 is connected directly to a source of positive potential and its emitter is connected to ground through resistor 76. The junction of the emitter of transistor 75 and resistor 76 is connected through resistor 77 and the forward junction of diode 78 to the base of transistor 67.

Photoresponsive element 79 is coupled to the incoming beta line and has a collector connected directly to a source of positive potential and an emitter connected both to a positive source through resistor 80 and to ground through resistor 81. The junction of the emitter of transistor 79 and resistor 81 is connected to the negative input of amplifier 82 the positive input of which is connected both to a source of positive potential through resistor 83 and to ground through rheostat 84. A feedback resistor 85 connects the ouput of amplifier 82 bacic to its negative input. The output of amplifier 82 is also connected through resistor 86 to the base of transistor 87 which has an emitter connected directly to ground and a collector connected to a source of positive potential through resistor 88.The collector of transistor 87 is also connected through resistor 89 to the base of transistor 90 which has an emitter connected directly to ground and a collector connected to a source of positive potential through resistor 91. An output is taken from the collector of transistor 90 and forms input TB1-8 to the CPU to which transceiver 44 is connected.

The data to be transmitted by transmitter 46 is supplied by the CPU over line TB1-5 to the base of transistor 92. The collector of transistor 87 is connected through the forward junction of diode 93 to the base of transistor 92.

This base is also connected to ground through resistor 94 and the emitter of transistor 92 is connected directly to ground whereas its collector is connected to a source of positive potential through resistor 95. The collector of transistor 92 is also connected through resistor 96 to the base of transistor 97 which has its emitter connected directly to ground and its collector connected from a source of positive potential through the series combination of resistor 98 and light emitting diode 99.

Light emitting diode 99 couples the data to be transmitted to the outgoing beta segment of transmission loop 1 6.

In order to block transmitter 46 from transmitting data when transceiver 41 is being used, line A-O is connected through resistor 100 to the base of transistor 101 the emitter of which is connected directly to ground and the collector of which is connected to a positive source through resistor 1 02. The collector of transistor 101 is connected through the forward junction of diode 103 to the base of transistor 92. As in the case of transceiver 41, transceiver 44 is connected to the CPU through an optical isolator which may be represented by diode 104, shown in phantom, between the output from receiver 45 and the input to transmitter 46.

When no data is transmitting, the fiber optic is under a no-light condition. When data is being transmitted, data bit 1 's are transmitted by a light condition and data bit O's are transmitted by a no-light condition. These data bits are received by photoresponsive transistor 51 and pulsed through amplifier 54 and inverted by transistors 59 and 61 and are presented to the output line 105 from receiver 42.

When a data bit one is received, phototrarisistor 51 conducts which results in the output from amplifier 54 going low and the output from transistor 59 going high. This high is connected to the base of transistor 67 through diode 66 and prevents transmitter 43 from transmitting this data bit back out of the CPU. When a data bit zero is received, transistor 51 no longer conducts so the output from amplifier 54 goes high, the output from transistor 59 goes low and the output from transistor 61 goes high which is connected through diode 65 to the base of transistor 67.

Thus, while transceiver 41 is receiving data, the base of transistor 67 is maintained high by diodes 65 and 66 to prevent this data from being retransmitted by the CPU. Simi larly, diodes 93 and 104 of transceiver 44 prevent the retransmission of data by transmitter 46 of the data received 45. When data is to be transmitted by transmitter 43, line A-O is turned to a low state which presents a high signal to the base of transistor 92 which blocks transmitter 46 from transmitting data.

Data is then supplied over the input line 106 to transmitter 43 and the light from LED 72 is then pulsed onto the beta segment coupled thereto. Receiver 45 and transmitter 46 operate similarly.

In Fig. 4, phototransistor 110 is coupled to the incoming alpha segment and has a collector connected directly to a source of positive potential and an emitter connected both to a source of positive potential through resistor 111 and to ground through resistor 11 2. The emitter of transistor 110 is also connected to the negative input of amplifier 11 3 the positive input of which is connected both to a source of positive potential through resistor 11 4 and to ground through variable resistor 11 5. Feedback resistor 11 6 connects the output from amplifier 11 3 back to its negative input.The output from amplifier 11 3 is also connected through resistor 11 7 to the base of transistor 11 8 the emitter of which is connected directly to ground and the collector of which is connected to a source of positive potential through resistor 11 9. The collector of transistor 11 8 is connected through resistor 121 to the base of transistor 120 which has its emitter connected directly to ground and its collector connected to a source of positive potential through resistor 1 22. The output line 1 23 connected to the collector of transistor 1 20 form the output from receiver A and is connected to the TP1 + A input to the DGP.Thus, as light pulses fall onto phototransistor 110, phototransistor 110 converts the light pulses into electrical pulses and supplies these pulses to output line 1 23.

The output line 1 24 is connected to input line 1 70 through the diode 1 24 shown in phatom. Input line 1 70 is also connected to output T50 - A from the DGP. The data on output line 1 23 is also connected by input line 1 70 to the base of transistor 1 25. The base of transistor 1 25 is also connected through resistor 1 26 to ground, the emitter is connected directly to ground, and the collector is connected to a source of positive potential through resistor 127.The collector of transistor 1 25 is connected through resistor 1 28 to the base of transistor 1 29 the emitter of which is connected directly to ground and the collector of which is connected from a positive source through the series combination of resistor 130 and light emitting diode 1 31.

Thus, the pulses that are received by phototransistor 110 are also transmitted back out on the alpha line by light emitting diode 131 and are also supplied to the data DGP by line 123.

Phototransistor 1 71 is coupled to the incoming beta segment in loop 1 6 and has a collector connected directly to a source of positive potential and an emitter connected both to a source of positive potential through resistor 1 72 and to ground through resistor 1 32. The emitter of transistor 1 71 is also connected to the negative input of amplifier 1 33 the positive input of which is connected both to a source of positive potential through resistor 1 34 and to ground through variable resistor 1 35. A feedback resistor 1 36 connects the output of amplifier 1 33 back to its negative input.The output of amplifier 1 33 is connected through resistor 1 37 to the base of transistor 1 38 the emitter of which is connected directly to ground and the collector of which is connected to a source of positive potential through resistor 1 39. The collector of transistor 1 38 is also connected through resistor 140 to the base of transistor 1 41 the emitter of which is connected directly to ground and the collector of which is connected to a source of positive potential through resistor 1 42. The collector of transistor 141 is connected to output line 143 which is connected to the input of the DGP to which transceiver 109 is connected.Output line 143 is also connected to the input line 144 of transmitter 107 through the diode 1 52 shown in phantom so that any input received by receiver 108 will be retransmitted by transmitter 107. Input line 144 is connected to the base of transistor 1 45 and to ground through resistor 146. The emitter of transistor 1 45 is connected directly to ground and its collector is connected to a source of positive potential through resistor 147. The collector of transistor 145 is also connected through resistor 148 to the base of transistor 1 49 the emitter of which is connected directly to ground and the collector of which is connected from a source of positive potential through series circuit of resistor 1 50 and light emitting diode 151.Light emitting diode 151 is coupled to the outgoing beta segment of loop 1 6. Diode 1 52 insures that received data is also retransmitted by transmitter 107. The DGP may transmit data out by supplying it over line 144 to transmitter 107. Diode 161 is connected from the collector of transistor 1 38 to the base of transistor 1 20 and diode 1 63 is connected from the collector of transistor 118 to the base of transistor 141.

Moreover, the collector of transistor 1 38 is connected through diode 1 64 to the base of transistor 1 25 to prevent transmitter 1 62 from transmitting when receiver 108 is receiving data. Likewise, the collector of transistor 11 8 is connected to the base of transistor 145 through diode 1 65 to insure that, when receiver 1 66 is receiving data, transmitter 107 is not transmitting data.

The above described data transmission system has several advantages. It is not vulnera bleito line cuts since transmission occurs in dual but opposite directions; cutting both of the optical fiber circuits anywhere in the loop will not disrupt normal communication. A second cut occurring between a different pair of stations will disrupt communication only with the stations between the cuts but will not effect communication with the remaining stations. Such a system is not vulnerable to undetected signal tapping since light signals within the fibre optic cable cannot be externally tapped without cutting the cable and any cut can be easily detected at the central processing unit.The transceivers in this system can be used as repeaters to minimise the effect of lossy optical couplers and, thus, there is virtually no limit to the number of stations which can be attached to a loop nor to the length of the loop. The dielectric nature of an optical fiber provides electrical isolation between the respective transmitter and receiver which eliminates ground loops. The optical fiber is immune to electromagnetic interference and does not itself radiate electromagnetic energy so that such a transmission system can be used in industrial applications and can carry signals near interference-prone electronic equipment. Expensive lightening and static protection circuitry is not required since the dielectric nature of the optical fiber eliminates the static and lightning pick-up problems which are present when conventional electrical cables are used. In addition, substantial cost savings can be realized because of the small size and light weight of the fibers and the relatively cheap and plentiful raw materials used to make them.

Claims

1. A data communications system comprising a plurality of stations; a first fiber optic transmission circuit connecting the stations in a loop configuration and enabling-optical data to be transmitted to the stations around the loop in a first direction; a second fiber optic transmission circuit connecting the stations in a loop configuration and enabling optical data to be transmitted to the stations around the loop in a second direction opposite to the first; each of the stations comprising a first transmitter/receiver connected to the first transmission circuit and a second transmitter/receiver connected to the second transmission circuit.

2. The system of Claim 1, wherein at least one of said stations is a data gathering panel, wherein the first transmitter is connected to the first receiver for retransmitting data received by the first receiver, and wherein the second transmitter is connected to the second receiver for retransmitting data received by said second receiver.

3. The system of Claim 2, wherein the respective transmitters and receivers are connected via a diode.

4. The system of Claim 2 or 3, wherein the first and second receivers each have corresponding outputs connected to said data gathering panel and the first and second transmitters have corresponding inputs connected to said data gathering panel.

5. The system of Claim 4, wherein said first and second fiber optic loop transmission circuits comprises a first and second plurality of segments respectively, each first receiver comprising a first photoresponsive device coupled to a corresponding one of said first plurality of segments, each first transmitter- comprising a first light emitting device coupled to another corresponding one of said first plurality of segments, each second receiver' comprising a second photoresponsive device coupled to a corresponding one of said second plurality of segments and each second transmitter comprising a second light emitting device coupled to another corresponding one of said second plurality of said segments.

6. The system of Claim 5, wherein at least one station is a central processing unit (CPU), wherein the first receiver of the CPU is connected to the first transmitter for preventing the retransmission of data received by the first receiver, and wherein the second receiver is connected to the second transmitter for preventing the retransmission of data received by the second receiver.

7. The system of Claim 6, including means connected between the first receiver of the CPU and the second transmitter for blocking the second transmitter when the first receiver is receiving, and means connected between the second receiver to the first transmitter for blocking the first transmitter when the second receiver is receiving.

8. The system of Claim 7, wherein the connecting means comprise diodes.