Data highway system with dual transmitting loop lines

A data highway system comprises a master station and a plurality of remote stations, connected through dual transmitting loop lines, and detecting means for detecting the breakage or disconnection of transmitting or substantially equal thereto, loop-back is automatically constituted responsive to the output of the detecting means to promptly return to normal condition.

BACKGROUND OF THE INVENTION 
The present invention relates to a data highway system with dual 
transmitting loop lines, and more particularly to a data highway system 
capable of returning to a normal operation by automatically forming a loop 
back pertinent to a break or disconnect of transmitting lines. 
Specifically, the present invention relates to a data higway system 
comprising a plurality of data stations connected through dual 
transmitting loop lines, and detecting means for detecting the break or 
disconnect of lines incorporated with each data station, thereby 
automatically detecting the break or disconnect of transmitting lines 
constituting a loop back in accordance with the line break. 
There have been proposed various kinds of data highway systems for 
transmitting data between data stations connected by loop transmitting 
lines. These data highway systems are suitable for various purpose, e.g. 
remote control of an electric power system including a large number of 
data stations. A well known transmitting system comprises a master 
station, and a plurality of slave stations independently connected to the 
master station by transmitting lines, a data highway system makes it 
possible to reduce the number of transmitting lines, thereby to provide a 
low cost system at a low cost. However, if the loop transmitting lines are 
broken or disconnected due to any trouble in the system, it is impossible 
to transmit the data, with the result that the system is down. 
Attempts have been made to eliminate these troubles which have been 
encountered with the data highway systems. 
For instance, there has been proposed a data highway system with dual 
transmitting lines in combination with a master station and a plurality of 
slave stations, wherein a break or disconnect line detecting command 
transmitted from the master station is scans between the slave stations; 
such a system is known as a "polling" technique. When a line break or 
disconnect occurs, the master station transmits a loop back command to the 
slave station via the broken or disconnected lines on the basis of the 
polling result. Connections are established to connect the first 
transmitting line to the second transmitting line so as to constitute a 
loop back to return to normal condition. However, with this method, it is 
impossible to have real time processing. Accordingly, it is difficult to 
apply this method to certain systems, e.g. an electric power system, where 
it is not permissible to temporarily interrupt the power. 
According to another prior art system, and "echo-back" method, such as, in 
a telephone system, is employed. This method is characterized by a 
synchronizing bit in a data format. The synchronizing bit is employed as 
an echo-back command. This method makes it possible to test terminal 
equipments by the echo-back command to determine whether each terminal 
equipment normally operates. However, this prior art system is not 
provided with the means for returning to normal condition. Accordingly, 
this prior art is not suitable for repairing the line breakage in an 
electric power system. 
In a telephone system, similar to the last mentioned prior art, when line 
breakage or disconnection is detected, the concerned terminal equipment 
connects the first transmitting line to the second transmitting line so 
that a loop back is formed and an alarm signal. The alarm signal is 
transmitted to the adjacent terminal equipment. The terminal equipment 
including a breakage line receives the alarm signal via a transmitting 
line that is loop-backed to recognize that the loop-back is established, 
thereby ceasing to produce the alarm signal. With this method, there is 
drawback that data derived while the loop-back is being formed is 
disregarded. 
SUMMARY OF THE INVENTION 
With the above in mind, an object of the present invention is to provide a 
data highway system with dual transmitting lines capable of automatically 
detecting a portion of a line where a break or equivalent malfunction 
occurs form a loop back, thereby preventing the transmitting function from 
being invalid. 
Another object of the present invention is to provide a data highway system 
with dual transmitting lines wherein remote or slave stations are able to 
detect a line break or equivalent malfunction of a transmitting line, 
wherein the detection is independent of the master station and is 
indicated by a simple line breaking or disconnect detecting means, such as 
two timers. 
A further object of the present invention is to provide a data highway 
system with dual transmitting lines wherein the system has simplified 
hardware and occupies only a small amount of space.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference is made to an embodiment of a data highway system according to 
the present invention. 
FIG. 1 is a block diagram schematically illustrating a loop back system 
employed in the data highway system with dual transmitting lines according 
to the present invention. 
The data station illustrated in FIG. 1 comprises a master station M and a 
plurality of remote or slave stations R.sub.1, R.sub.2, . . . , and Rn. 
The master station M is connected to the plurality of remote stations 
R.sub.1, R.sub.2, . . . , and Rn through first and second 
loop-transmitting lines L.sub.1 and L.sub.2 wherein each information 
signal passing through the lines L.sub.1 and L.sub.2 is transmitted in the 
opposite direction as indicated by arrow. A separate information 
processing unit PU is connected to the data station M and the plurality of 
information processing units R.sub.1, R.sub.2, . . . , and Rn. The 
information processing unit PU performs predetermined processing on data 
transferred to each data station. The master station M includes a 
substation SB which is formed similarly to the remote stations R.sub.1, 
R.sub.2. . . R.sub.n. 
A break line or disconnection in either of the first and second lines or 
both lines. It is also assumed that there happens substantially the same 
condition as that of the line breakage because of the interruption of 
power supply provided in the data station, or faults the transmitter 
and/or the receiver incorporated therein. 
The method of detecting such a condition and retrieving therefrom will be 
described below. 
The master station M transmits signals in opposite directions to the first 
and second lines L.sub.1 and L.sub.2. Each remote station R.sub.1, 
R.sub.2, . . . Rn and master station M captures or relays and regenerates 
data received thereby, as transmitted through the first and second 
transmitting lines Lhd 1 and L.sub.2 ; the remote station responds to the 
received information and transmits the information contained in the data 
signal to the neighboring station. Thus, remote station R.sub.K responds 
to a data signal supplied to it from station R.sub.K-1 via line L.sub.1 
and transmits the first data signal via line L.sub.1 to station R.sub.K+1 
; station R.sub.K responds to a second data signal supplied to it from 
station R.sub.K+1 via line L.sub.2 and transmits the second data signal to 
station R.sub.K+1 via line L.sub.2. The method of transmitting data 
comprises the steps of interrupting the relaying and regenerating in the 
first transmitting line, and shifting a gate (not shown). Each station 
comprises one serial/parallel converter circuit. Each station has two sets 
of transmitters and receivers corresponding to the dual transmitting lines 
L.sub.1 and L.sub.2. Each remote station R.sub.1, R.sub.2, . . . , 
R.sub.n, but not master station M, has two sets of retrigger timers 
T.sub.1 and T.sub.2 having different durations (T.sub.1, T.sub.2). Timers 
T.sub.1 and T.sub.2 are connected to the outputs of receivers in the 
remote station responsive to the first and second transmitting lines 
L.sub.1 and L.sub.2, to determine whether a signal exists in the 
transmitting lines or not. 
Assume that a signal on line L.sub.1 or L.sub.2 disappears because the line 
carrying the signal breaks. In response to the line break, there is a 
swift in the output status of timer T.sub.1 provided in the remote station 
directly connected to the broken transmitting line or lines, e.g., timer 
T.sub.1 goes from "H" to "L" (time up). In response to this operation, 
dummy data are transmitted to the neighboring remote station. Further, in 
the case of a line break, all the remaining remote stations which are 
located downstream of the broken line portion are placed in a non-signal 
condition. As a result, there is a shift in the output status of the 
timers T.sub.1 provided in the remaining remote stations, e.g., from "H" 
to "L" (time up). Thus, as stated above, dummy data are transmitted in 
turn to the neighboring remote stations due to the actuation of the timers 
T.sub.1. A predetermined time (T.sub.1) after the break indication is 
transmitted to the remaining remote stations, i.e., the remote stations 
different from the remoate station where the line breaks, the timers 
T.sub.1 in the remaining remote stations return to an initial condition, 
that is, shift in output status, e.g., from "L" to "H". This return occurs 
because the dummy data are transmitted to these remote stations. Since a 
dummy data signal is not transmitted to the remote stations. Since a 
dummary data signal is not transmitted to the remote station directly 
connected to the broken transmitting line, the timer t.sub.2 provided in 
the remote station directly connected to the broken transmitting line 
shifts output status from "H" to "L". The shift from "H" to "L" of timer 
T.sub.2 at the remote station directly connected to the broken line 
enables master station M to recognize where the line break has occurred in 
the transmitting lines. 
The above method and the simplified circuit at each remote station makes it 
possible to detect the break in the transmitting lines. 
Consideration is now given to forming a loop after the line break is 
detected, in elation to the case of the line break in the first 
transmitting line L.sub.1, the second transmitting line L.sub.2, or both 
lines L.sub.1 and L.sub.2. 
First, let us suppose that a break occurs in the first transmitting line 
L.sub.1 between stations R.sub.1 and R.sub.2. As shown in FIG. 2, the data 
received by station R.sub.2 via the second transmitting line L.sub.2 is 
loop-backed to the first transmitting line L.sub.1 via station R.sub.2. 
Simultaneously with this, the data transmission from station R.sub.2 to 
station R.sub.1 through the second transmitting line L.sub.2 is 
interrupted. In the reamining data stations positioned on the both sides 
of the broken line portion, the data transmitted through the second 
transmitting line L.sub.2 to station R.sub.1 are not received by station 
R.sub.1. Instead, data received by station L.sub.1 via the first 
transmitting line L.sub.1 are looped back from station R.sub.1 so they are 
transmitted to station M via the second transmitting line L.sub.2. 
Thus, loop-back is performed in both of the remote stations R.sub.1 and 
R.sub.2 on opposite sides of the location where the line breaks. Each 
remote station R.sub.1, R.sub.2, . . . R.sub.n which detects a line break 
transmits information indicating that it has detected a break to the 
master station M in response to a specified command from the master 
station M. However, even if the loop back is formed in the transmitting 
line L.sub.1, two loops are formed at the boundary of the location of the 
line break in the flow of information as shown by label X.sub.1. The 
master station M responds solely to the data transmitted from the station 
positioned forward with respect to the line break. The master station M 
considers the transmitting line as being in a break condition, in response 
to information indicating the line break, as derived from the remote 
stations R.sub.1, R.sub.2, . . . Rn or when a response occurs from the 
remote station positioned forward of the remote station immediately 
adjacent the break. In such a situation, the master station M transmits 
the received data coupled to it via the second transmitting line L.sub.2 
to a remote station on the opposite side of station M via second 
transmitting line L.sub.2. 
Consider the situation of a line break of the second transmitting line 
L.sub.2 between remote stations R.sub.1 and R.sub.2 shown in FIG. 3. The 
break is detected at station R.sub.1, causing a loop-back to be formed to 
couple the data received by station R.sub.1 on line L.sub.1 to be fed back 
to master station M, with an indication of the location of the data break, 
via the second transmitting line L.sub.2. 
Each of master station M and remote stations R.sub.1, R.sub.2, . . . Rn 
receives a data signal via the first transmitting line L.sub.1 and 
transmits the data signal received on line L.sub.1 to the next station via 
the first transmitting line L.sub.1, where station M transmits a data 
signal to station R.sub.1 via line L.sub.1, station R.sub.K transmits a 
data signal to station R.sub.K+1 via line L.sub.1 and station Rn transmits 
a data signal to station M via line L.sub.1, where k is selectively every 
integer from 2 to (n-1). Accordingly, even if a line break occurs in the 
second transmitting line L.sub.2, there is no inconvenience in 
transmitting or receiving the data. For this reason, in the case of a 
break in the second transmitting line L.sub.2 between stations R.sub.1 and 
R.sub.2, an information signal indicating a line break at station R.sub.1 
is coupled back to station M from station R.sub.1 via line L.sub.2. The 
signal transmitted from station M to station R.sub.1 via line L.sub.1 is 
coupled to stations R.sub.2. . . Rn via line L.sub.1, as indicated by 
label X.sub.2, FIG. 3. 
In the case for a break in both transmitting lines L.sub.1 and L.sub.2 
between stations R.sub.1 and R.sub.2, as shown in FIG. 4, the line break 
is detected in both stations R.sub.1 and R.sub.2 adjacent the portion of 
the line where the break occurs; detection at stations R.sub.1 and R.sub.2 
results in two loop-back networks being formed. One network is from 
station M to station R.sub.1 via lines L.sub.1 and L.sub.2 ; the other 
network is from station M to station R.sub.2 via lines L.sub.2 and L.sub.1 
via stations R.sub.n. . . R.sub.3 (not shown). The processing in this case 
is substantially the same as that which occurs for a line break in the 
first transmitting line L.sub.1. In the case of the first transmitting 
line L.sub.1, the loop back is formed at the data station R.sub.1 where 
the break of the first transmitting line L.sub.1 is detected. 
Simultaneously, the transmission of the data by the second transmitting 
line L.sub. 2 is interrupted, thus forming the same condition as for a 
break of the second transmitting line L.sub.2. 
For this reason, when the loop back is formed at both stations surrounding 
the broken line portion, there is a time difference in the break 
indicating signals arriving at station M via lines L.sub.1 and L.sub.2. 
The flow of the information is indicated by label X.sub.3. 
Reference is made to the treatment in connection with the line break in 
both ends of the master station M. 
The master station M comprises two timers T.sub.1 having time T.sub.1 
required for timing up. One of timers T.sub.1 is connected to the output 
of the receiver in station M connected to the first and second 
transmitting lines L.sub.1 and L.sub.2. In this case, the master station M 
does not comprise timer T.sub.1. 
For instance, if a line break occurs in the second transmitting line 
L.sub.2 between stations R and M, i.e., at the receiver side of station M 
connected to line L.sub.2, as shown in FIG. 5A, there is no inconvenience 
in transmitting or receiving information on first transmitting line 
L.sub.1. In this case, the line break is detected because timer T.sub.2 in 
receiver R becomes operative in response to the break in the second 
transmitting line L.sub.2. 
As shown in FIG. 5B, if a break occurs between stations M and R in the 
first transmitting line L.sub.1, at the transmitting end of station M 
connected to line L.sub.1, the line break is detected in the remote 
station R receiving the data transmitted on the first transmitting line 
L.sub.1. Thus, a loop-back is formed, so that the information indicating 
the break location is transferred to the master station M. In this case, 
there is no inconvenience in transmitting or receiving the data. In the 
case for breaks in both transmitting lines L.sub.1 and L.sub.2, the above 
treatments are simultaneously carried out, thereby forming one closed 
loop. If a break occurs in the receiving end of the second transmitting 
line L.sub.2 between stations M and R, i.e., at the transmitter end of 
station M connected to line L.sub.2, the usual treatment in connection 
with a break in the second transmitting line L.sub.2 is carried out in the 
remote station R, as shown in FIG. 5C. In the event that a break occurs 
between station M and R in the receiving end of station M responsive to 
the signal transmitted on the first transmitting line L.sub.1, station M 
detects the break in the first transmitting line L.sub.1 at the same time 
it interrupts the reception of data via line L.sub.1 and transmits the 
data via the second transmitting line L.sub.2, as illustrated. The remove 
station in the neighborhood of the receiving end of the second 
transmitting line considers that the break occurs in the secod 
transmitting line L.sub.2. Thus, as shown in FIG. 5D, the loop-back is 
formed. Since there are no data received by station M from the first 
transmitting line L.sub.1, the transmitting line is shifted to a mode 
wherein station M receives the data from the second transmitting line 
L.sub.2. 
The detailed circuit diagrams of the master station, and each remote 
station are described with reference to FIGS. 6 and 7. 
FIG. 6 is a block diagram of one example of the internal construction of 
the master station M containing transmitting control unit 6 including a 
serial/parallel converting circuit. The data transmitted to station M via 
the first receiving/transmitting line (L.sub.1) 12 and the second 
receiving/transmitting line (L.sub.2) 13 are received by receivers 8A and 
8B. The signals received by receivers 8A and 8B are transmitted to the 
T.sub.2 timers 9A and 9B which produce a signal having a duration T.sub.2 
required for timing up. The signal indicating the remote station where a 
break occurs in the first transmitting line L.sub.1 is derived as an 
output from timer 9A on lead 21 and transmitted to the transmitting 
control unit 6. 
The outputs of the receivers 8A and 8B and the output of the timer 9A are 
fed to a logical circuit LG.sub.1. The logical circuit LG.sub.1 comprises 
AND gates AND.sub.1, and AND.sub.2, and OR gate OR.sub.1, as well as 
inverter IN.sub.1. Gate OR.sub.1 derives an output signal on lead 18 which 
is fed to the transmitting control unit 6. 
The output of the timer 9B on lead 22 is fed to the transmitting control 
unit 6 indicative of a break in the second transmitting line L.sub.2. 
Circuit 6 responds to the signals on leads 18, 21 and 22 to derive a gate 
signal on lead 14 and a data signal on lead 19. The output signals from 
timers 9A and 9B are combined with the signals on leads 14 and 19 in logic 
circuit LG.sub.2, including AND gates AND.sub.3, AND.sub.4 and OR gate 
OR.sub.2, as well as inverter IN.sub.2 and AND gate AND.sub.5 having first 
and second input terminals respectively connected to the outputs of OR 
gate OR.sub.2 and timer 9A. The output of logical circuit LG.sub.2 is 
coupled to the transmitter 7B, having an output connected to the 
transmitting line 11 of the second transmitting system L.sub.2. The 
transmitted data signal on lead 19 is fed to the transmitter 7A, having an 
output fed to the transmitting line 10 of the first transmitting system 
L.sub.1. 
FIG. 7 is a circuit diagram of the internal construction in the remote 
stations R, R.sub.1, R.sub.2, . . . Rn. 
The signals received by the remote station from the first 
receiving/transmitting line (L.sub.1) 12 and the second 
receiving/transmitting line (L.sub.2) 13 are received by the receivers 28A 
and 28B. The output of the receiver 28A is fed to the timer 15A having a 
time T.sub.1 required for timing up and the timer 29A having a time 
T.sub.2 required for timing up. Each of the timers 15A and 29A has an 
output fed to the dummy data deriving circuit 16A. The output of T.sub.2 
timer 29A is fed to the transmitting control unit 26 as a signal 
indicative of a break of the first transmitting system L.sub.1. 
The output of the receivers 28A and 28B and the output of the timer 29A are 
transmitted to a logical circuit LG.sub.3 comprising AND gate AND.sub.6 
and AND.sub.7, and OR gate OR.sub.3, and inverter IN.sub.3. OR gate 
OR.sub.3 derives a logic output F.sub.1 fed to the transmitting control 
circuit 26. The output of the receiver 28B is fed to T.sub.1 and T.sub.2 
timers 15B and 29B and, having outputs fed to the dummy data transmitting 
gate circuit 16B. The otput of T.sub.2 timers 29B is fed to the 
transmitting control unit 26 as a signal indicative of a break of the 
second transmitting system L.sub.2. 
Transmitted data derived from circuit 26 on lead 19 and a gate signal 
derived from circuit 26 on lead 20 are combined with the first output 
f.sub.1 of the logic circuit LG.sub.3 are fed in logic circuit LG.sub.4, 
comprising AND gates AND.sub.8 and AND.sub.9, OR gate OR.sub.4, and 
inverter IN.sub.4. 
The output of the logic circuit LG.sub.4, the second output of the logic 
circuit LG.sub.3, and the signal on lead 22 indicative of a break in the 
second transmitting system L.sub.2, as derived as an output of the timer 
29B, are fed to a logical circuit LG.sub.5 comprising AND gates AND.sub.10 
and AND.sub.11, and OR gate OR.sub.5. The logic output of the logical 
circuit LG.sub.5, the output of the dummy data transmitting gate circuit 
16B and the dummy data fed from the transmitting control unit 26 on lead 
17 are fed to a logical circuit LG.sub.6. Comprising AND gates AND.sub.12, 
and AND.sub.13, OR gate and OR.sub.6, and inverter IN.sub.6. The logical 
output of the logical circuit LG.sub.6 is fed to the transmitter 27B. The 
output of the transmitter 27B is fed to the transmitting line 17 of the 
second transmitting system (L.sub.2). The output of the dummy data 
transmitting gate circuit 16A, the logical output of the logical circuit 
LG.sub.4, and the dummy data on lead 17 fed from the transmitting control 
unit 26 are fed to the logical circuit LG.sub.7, having logical output fed 
to the transmitter 27A. The output of the transmitter 27A is fed to the 
transmitting line 10 of the first transmitting system (L.sub.1). 
The internal comstruction and the operation of the data station has been 
previously described. According to a break condition, such as a break of 
the first transmitting system, a break of the second transmitting system, 
and a break of the both transmitting systems, the loop back is form, 
thereby making it possible to interrupt the transmitting function. 
According to the present invention, in a loop-data highway system wherein a 
plurality of data stations are connected by the double transmitting line 
in which the transmitting direction is different to each other, when a 
break in a single or double transmitting system occurs, or when a 
condition equivalent to the break occurs, e.g., due to an interruption of 
the power supply of the data station or trouble with the transmitter and 
receiver, the break is automatically detected by the two timers, each 
having different time constant, assembled in each data station. Thus, 
loop-back is formed due to the breakage of the first second or both 
transmitting systems. This system makes it possible to continue the 
transmitting function with the simplified construction. 
It is to be understood that modifications and variations of the embodiments 
of the present invention disclosed herein may be restored to without 
departing from the spirit of the invention and the scope of the appended 
claims.