Bus-method communication network system capable of seizing transmission right by using timer means at each station

A bus-method communication network has a number of stations with assigned station numbers. An exclusive right or priority of transmission is transferred from a first station to a second station by transmission of an abort signal including synchronization information and a first address assigned to the first station. In each station, a waiting time is calculated from a first station number in the detected abort signal and the station number assigned to the receiving station. When the associated waiting time elapses, another station seizes priority as a second station and transmits a paging signal having a destination address following communication data. Each station is prevented from seizing transmission priority in response to reception of the paging signal, and the station having the destination address decodes the communication data. The second station thereafter transmits the abort signal. Each station monitors any signal on the transmission line after reception of the paging signal on the transmission line after reception of the paging signal, and measures times lapse over a period determined by its assigned address number when detecting no transmitted signal. The station having the smallest address number transmits the abort signal as a first station when the time period elapses. Each station can delay transmission of the abort signal by another time period determined by the total number of stations, when the second station has no communication data.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to a bus-method communication network system 
comprising a plurality of stations connected by a bus-method transmission 
path so as to commonly use the transmission path for mutual communication 
of the stations. 
(2) Description of the Prior Art 
A local area network communication system has been recently developed in 
order to connect a plurality of stations which are distributed in a 
relatively narrow area. A bus-method communication network system is a 
typical one of the local area network system. 
The bus-method communication network system comprises a bus-method 
transmission path and the stations which are assigned with station numbers 
different from one another. The stations are commonly connected to the 
transmission path so as to commonly use the transmission path for mutual 
communication of the stations. 
In the bus-method communication network system, contention occurs for 
seizing a transmission right or priority as is well known in the art. In 
order to resolve the contention, various methods have been already known 
in the art for accessing the transmission path, or seizing an exclusive 
transmission right. 
A known access method is a carrier sense multiple access with collision 
detection (CSMA/CD) method. In the CSMA/CD method, each station always 
performs carrier detection on the transmission path. One station transmits 
a signal after confirming that none of other stations transmits any 
signal. On detection of collision, the station stops transmission of the 
signal and tries to retransmit the signal after the lapse of a random time 
period. However, the CSMA/CD method is disadvantageous in that processing 
is complicated for seizing the transmission right. 
A polling protocol is another access method. In the polling protocol, a 
master controller is connected to the transmission path. The master 
controller transmits a polling sequence to one of the stations in order to 
poll or interrogate about absence or presence of a transmission request. 
The polled station transmits a data signal when the transmission request 
is present, while the polled station transmits a negative acknowledge in 
absence of the transmission request. Accordingly, the polling protocol is 
disadvantageous in that the bus-method communication network system is 
expensive because the master controller is necessary for polling the 
stations. In addition, it is impossible to effectively use the 
transmission path for increased number of stations. This is because the 
controller spends a lot of time for polling in comparison with actual 
communication. 
A token passing method is still another access method. In the token passing 
method, a token is transferred along a predetermined logical ring of the 
stations one after another. A specific station in the logical ring seizes 
the exclusive transmission right by capture of the token. Then, the 
specific station sends out communication data to the transmission path if 
there are any, and sends out the token after the data are completely 
transmitted. In absence of data which should be transmitted, the specific 
station immediately transmits the token. In the token passing method, 
extinction and duplication of the token should be observed. Therefore, one 
or more supervising stations must be provided for monitoring the token and 
recovering the token from such faults, or one or more stations must be 
arranged to have such a supervising function. In addition, the logical 
ring must be dynamically determined for permitting another station to join 
to, or retire from, the logical ring, and the resultant logical ring must 
be maintained without fault. Accordingly, the token passing method is 
disadvantageous in that the bus-method communication network system is 
very expensive because the supervising is a very complex and difficult 
processing. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a bus-method communication 
network system which is economical and can effectively use a bus-method 
transmission path with the exclusive transmission right or priority being 
reliably seized in each of the stations without duplication, and wherein 
each station is simple in arrangement and processing for seizing the 
transmission right. 
The present invention is directed to a bus-method communication network 
system comprising a bus-method transmission path and a plurality of 
stations commonly connected to the transmission path for mutual 
communication therebetween, the stations being assigned with station 
numbers different from one another, a specific one of the stations having 
an exclusive transmission right to access to the transmission path at a 
specific time without the other stations being permitted to access 
thereto, the specific station transmitting an abort signal representative 
of abandonment of the exclusive transmission right to the transmission 
path, one of the other stations freshly seizing the exclusive transmission 
right by detecting the abort signal. According to the present invention, 
the system is characterized in that the specific station has, as a 
specific station number, a station number assigned thereto and the abort 
signal comprises synchronization information and the specific station 
number. In each one of the stations, station number memorizing means is 
provided for storing, as a preassigned station number, one of said station 
numbers assigned thereto. Receiver means is coupled with the transmission 
path for receiving a transmission signal on the transmission path. Abort 
signal detecting means is coupled with the receiver means for detecting 
the abort signal in the transmission signal received by the receiver means 
and extracting the specific station number in the abort signal as 
detected. The abort signal detecting means produces an abort detection 
signal and an address signal representative of the specific station number 
as extracted. Time calculating means is coupled with the station number 
memorizing means and the abort signal detecting means for calculating a 
first time period depending on the extracted specific station number and 
the preassigned station number to produce a first time data signal 
representative of the first time period. First time measuring means is 
responsive to the first time data signal and measures time to produce an 
output, as a first enabling signal, when the first time period elapses. 
Seizing decision means is responsive to the first enabling signal and 
decides permission of seizure of the exclusive transmission right to 
produce a seizing signal when the permission is decided, whereby one of 
the stations other than the specific station freshly seizes the exclusive 
transmission right. 
Each one of the stations further comprises transmitter means coupled with 
the transmission path for transmitting a specific transmission signal to 
the transmission path and first data storing means for storing 
communication data to be transmitted to the transmission path. 
Transmission control means responsive to the seizing signal checks whether 
or not any communication data are in the first data storing means and 
sends out, when communication data are present, the communication data 
from the first data storing means to the transmitter means for the 
specific transmission signal. The transmission control means produces an 
abort control signal when any communication data are absent in the first 
data storing means. Abort signal send-out means stores the abort signal 
which comprises the synchronization information and the preassigned 
station number as the specific station number. The abort signal send-out 
means, in response to said abort control signal, sends out the abort 
signal to the transmitter means for the specific transmission signal. 
Each one of the stations further comprises paging signal generating means 
responsive to a transmission control signal for sending out a paging 
signal to the transmitter means. The paging signal comprises destination 
address for designating a station as a destination station to which the 
communication data are transferred and enquiry information for requesting 
response to the paging signal for the destination station. The 
transmission control means produces the transmission control signal prior 
to sending out of the communication data. 
Each one of the stations further comprises paging signal detecting means 
for detecting the paging signal in the transmission signal received by the 
receiver means to produce an output signal as a non-permission signal. The 
paging signal detecting means further extracts the destination address in 
the paging signal to produce a destination address signal representative 
of the destination address as extracted. The seizing decision means is 
coupled to the paging signal detecting means and holds a non-permission 
condition in response to the non-permission signal. The seizing decision 
means decides not permission but non-permission in response to the first 
enabling signal to change the non-permission to a permission condition 
without producing the seizing signal when the non-permission condition is 
held. 
Each one of the stations further comprises coincidence detecting means 
coupled with the station number memorizing means and responsive to the 
destination address signal for detecting coincidence between the 
preassigned station number and the destination address as extracted. The 
coincidence detecting means produces a coincidence signal when the 
coincidence is detected. In response to the coincidence signal, reception 
control means produces a reception control signal. Second data storing 
means is responsive to the coincidence signal and stores communication 
data in the transmission signal received by the receiver means. 
In each of the stations, the coincidence detecting means produces a 
non-coincidence signal when detecting no coincidence. Each station may 
further comprise signal monitoring means responsive to the non-coincidence 
signal for monitoring whether or not the transmission signal is present on 
the transmission path to produce a monitored signal when the transmission 
signal is present on the transmission path, time data generating means 
responsive to the monitored signal for generating a second time data 
signal, the second time data signal being representative of a 
predetermined second time period, and second time measuring means 
responsive to the second time data signal for measuring time to produce an 
output signal, as a second enabling signal, when the second time period 
elapses. The seizing decision means is also coupled with the second time 
measuring means and, in response to the second enabling signal, decides 
permission of seizure of the exclusive transmission right to produce the 
seizing signal when the permission is decided. 
Each one of the stations may also comprise timer means operating in 
response to a timer start signal and producing a timer output signal after 
a predetermined time duration. The transmission control means is made to 
produce, in response to the seizing signal, the timer start signal when 
any communication data is absent in the first data storing means. The 
transmission control means is responsive to the timer output signal and 
further checks the first data storing means. Then, the transmission 
control means produces a first abort control signal when any communication 
data are absent in the first data storing means. The abort signal send-out 
means is responsive to the first abort control signal and sends out the 
abort signal to the transmitter means. The transmission control means is 
responsive to the seizing signal and/or the timer output signal and sends 
out on presence of the communication data in the first data storing means 
the communication data to the transmitter means for the specific 
transmission signal. The transmission control means produces a second 
abort control signal when the transmission of said communication data is 
completed. The abort signal send-out means also sends out the abort signal 
to the transmitter means in response to the second abort control signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a bus-method communication network system according to 
this invention comprises a plurality of stations (five stations are shown 
by way of example only) 20-24. The stations 20 through 24 are assigned 
with the station numbers which are equal to "0" through "4", respectively. 
The stations 20 to 24 are commonly connected to a bus-method transmission 
path 26 of a serial data bus so as to commonly use the transmission path 
26 for mutual communication of the stations 20 to 24. 
At a specific time, a specific one of the stations 20 to 24 has the 
exclusive transmission right to transmit a paging signal E (FIG. 2) and 
thereafter its communication data to the transmission path 26. At that 
time, the other stations are prevented by reception of the paging signal 
from transmitting the data to the transmission path 26. When the specific 
station has no communication data to be transmitted or finishes 
transmission of the data, it transmits an abort signal S (FIG. 3) 
representative of abandonment of the exclusive transmission right to the 
transmission path 26. One of the other stations seizes the exclusive 
transmission right by detecting the abort signal S as will later be 
described. 
Each station 20-24 is arranged similar to one another. Accordingly, 
description will be made as to an arrangement of one station according to 
an embodiment of the present invention with reference to FIG. 4. 
Referring to FIG. 4, the station comprises a station number memory 30 for 
storing the station number preassigned to the station. The station number 
is supplied to the station number memory 30 by means of, for example, a 
number input device such as a numerical selector switch or a ten-key 
device (not shown). 
The station comprises a transmitter 31 for transmitting a transmission 
signal to the transmission path 26 and a receiver 32 for receiving the 
transmission signal transferred through the transmission path 26. The 
transmitter 31 is coupled with the transmission path 26 and has a 
parallel/serial (P/S) converter 33. The P/S converter 33 converts the 
transmission signal from a bit parallel to bit serial form and delivers 
the transmission signal of a bit serial form to the transmission path 26. 
The transmitter 31 also serves to convert logic code of the data into 
transmission code. 
The receiver 32 is also coupled with the transmission path 26 and has a 
serial/parallel (S/P) converter 34 which converts the received signal from 
a bit serial to bit parallel form. The receiver 32 also converts the 
transmission code into the logic code. In this embodiment, the data of the 
bit parallel form comprises 8 bits in length. 
The station comprises a first data storage 35 for storing communication 
data which is supplied from an external unit for transferring the data 
from the station to another station. The communication data are read to 
the transmitter 31 from the first data storage 35 under control of a 
transmission controller 36. 
A paging signal generator 37 is coupled with the station number memory 30 
and the first data storage 35. The paging signal generator 37 generates a 
paging signal E under control of the transmission controller 36. 
The paging signal E has a signal format as illustrated in FIG. 2. The 
signal format comprises an enquiry field ENQ in which enquiry information 
is inserted, a destination address field DA which identifies an address or 
a number of a station for which the communication data stored in the first 
data storage 35 are intended to be transmitted, a sender, source, or 
specific address field SA for identifying the station number preassigned 
to its own station, the check field BCC in which the check code is 
inserted. The inquiry information ENQ is for requesting a response to the 
paging signal for a station designated by the address in the destination 
address field. 
Referring to FIG. 4 again, the station further comprises an abort signal 
sender 38 for sending out the abort signal S through the transmitter 31 to 
the transmission path 26 under control of the transmission controller 36, 
as will later be described. 
The abort signal S has a signal format as illustrated in FIG. 3. The signal 
format comprises a synchronization field SYN in which a synchronization 
code is inserted, the source or specific address field SA which has the 
station number N preassigned to its own station, and the check field BCC 
having the check code. 
The signal fields and the corresponding signals may often be represented by 
the same reference symbols. 
Returning to FIG. 4, the station further comprises a second data storage 
39. The communication data are received by the receiver 32 and are stored 
in the second data storage 39 under control of a receiver controller 40. 
The communication data stored in the second data storage 39 is read out by 
an external unit (not shown) requiring the communication data. 
To the receiver 32, an abort signal detector 41 and a paging signal 
detector 42 are connected in addition to the second data storage 39. 
The abort signal detector 41 detects the abort signal S in the signal 
incoming thereto through the receiver 32. The abort signal detector 41 
produces an abort detect signal ADS on detecting the synchronization field 
SYN, and then extracts the specific address SA in the detected abort 
signal S. 
The paging signal detector 42 detects the paging signal E in the signal 
incoming thereto through the receiver 32. In detail, when the paging 
signal detector 42 detects the enquiry ENQ, it produces a paging detecting 
signal PDS representative of the enquiry character. When detecting the 
destination address DA, the paging signal detector 42 extracts the 
destination address DA. On detection of the specific address SA, the 
paging signal detector 42 compares the specific address SA and the 
preassigned station number N assigned to its own station and produces a 
non-permission signal NPS when the both are not coincident with each 
other. A comparator 42a for performing the comparing operation is shown in 
the block of the paging signal detector 42. 
The station further comprises a seizing control unit 43 for controlling the 
transmission controller 36. 
The seizing control unit 43 comprises a time calculator 44 and a time 
measuring circuit or a timer 45. 
The time calculator 44 calculates an initial time period T.sub.0 in 
response to a start signal or a power-on signal when the bus-method 
communication network is started up. 
The initial time period T.sub.0 is related to the preassigned station 
number N by; 
EQU T.sub.0 =(N+1).times.t (1), 
where t represents a predetermined short unit time. 
Responsive to the abort detect signal and the extracted specific station 
number SA from the abort signal detector 41, the time calculator 44 also 
calculates a waiting time period T.sub.1 which is related to a difference 
number between the specific station number SA and the preassigned station 
number N stored in the station number memory 30. 
The waiting time period T.sub.1 is defined by the following equation; 
##EQU1## 
where W represents the total number of the stations in the network system. 
The initial time period T.sub.0 and the waiting time period T.sub.1 are set 
in the timer 45. 
The timer 45 starts time measuring when a time period is set thereinto and 
produces an output signal when the set time period elapses. The timer 45 
is a resetable type wherein a time period set therein can be changed from 
a previously set time period to another time period newly supplied thereto 
even before the previously set time period elapses. 
Accordingly, after the initial timer period T.sub.0 is set in the timer 45, 
the waiting time period T.sub.1 can be set in the timer 45 without 
producing any output signal from the timer 45, when the waiting time 
period T.sub.1 is supplied to the timer 45 before the initial time period 
T.sub.0 elapses. 
As the timer 45, a presetable pulse counter can be used which counts clock 
pulses up to a maximum value set therein and produces an output signal. 
When a fresh value is supplied to the counter during counting operation, 
the count is reset and the value is set as a new maximum value. 
The control unit 43 further comprises a seizing decision circuit 46. 
The seizing decision circuit 46 is for deciding whether or not its own 
station can seize the exclusive transmission right. The seizing decision 
circuit 46 is provided with a register 47 for maintaining the 
non-permission signal NPS from the comparator 42a in paging signal 
detector 42. When the seizing decision circuit 46 receives an output 
signal, as an enabling signal ES, from the timer 45, it checks the content 
of the register 47. When the register 47 has the non-permission signal 
NPS, the seizing decision circuit 46 delete the non-permission signal NPS 
in the register 47. When the register 47 does not have the non-permission 
signal NPS, the seizing decision circuit 46 produces a seizing signal SS 
to the transmission controller 36. 
Responsive to the seizing signal SS, the transmission controller 36 checks 
whether any communication data are present or absent in the first data 
storage 35. The transmission controller 36 produces a transmitting control 
signal TCS when communication data to be transmitted are present in the 
first data storage 35. The transmission controller 36 produces an abort 
control signal ACS when data to be transmitted are absent in the first 
data storage 35. 
In response to the abort control signal ACS, the abort signal sender 38 
sends out the abort signal S through the transmitter 31 to the 
transmission path 26. 
In response to the transmitting control signal TCS, the paging signal 
generator 37 generates the paging signal E which is sent out through the 
transmitter 31 to the transmission path 26. After the paging signal E is 
completed, the transmission controller 36 accesses the first data storage 
35 to transmit the communication data from the first data storage 35 
through the transmitter 31 to the transmission path 26. After the 
communication data stored in the first data storage 35 is sent out 
completely, the transmission controller 36 generates the abort control 
signal ACS, so that the abort signal sender 38 sends out the abort signal 
S to the transmission path 26. 
The destination address DA extracted by the paging signal detector 42 is 
supplied to a coincidence detector 48 and is compared with the preassigned 
station number N stored in the station number memory 30. The coincidence 
detector 48 produces a coincidence signal CS when the coincidence is 
detected between the destination address DA and the preassigned station 
number N. 
The coincidence signal is applied to the reception controller 40, and the 
reception controller 40 produces a reception control signal RCS to control 
the second data storage 39 so that the communication data received by the 
receiver 32 through the transmission path 26 are stored into the second 
data storage 39. 
Operation of the bus-method communication network system of FIG. 1 with 
each station having the construction of FIG. 4 will be described below 
with reference to FIGS. 5-7. 
At first, it is assumed that each station 20-24 has no communication data 
to be transmitted. 
Referring to FIG. 6 together with FIG. 5, when the power is turned on in 
the bus-method network system of FIG. 1, the power-on signal is supplied 
to the time calculator 44 in each station. The time calculator 44 
calculates the initial time period T.sub.0 according to equation (1). 
Accordingly, the initial time periods T.sub.0 (20), T.sub.0 (21), T.sub.0 
(22), T.sub.0 (23), and T.sub.0 (24) of stations 20 to 24 are equal to t, 
2t, 3t, 4t, and 5t, respectively, because stations 20-24 are assigned with 
the station numbers of "0" to "4", respectively. In each station 20-24, 
the initial time period T.sub.0 is set in the timer 45 (step 101 in FIG. 
5). The timer 45 starts the time measuring (step 102 in FIG. 5) and 
produces the enabling signal ES to the seizing decision circuit 46 when 
the initial time period T.sub.0 elapses. The enabling signal ES is 
produced at first in station 20 having a station number "0". This is 
because the station 20 has the shortest initial time period T.sub.0 
(20)=t. 
In station 20, the seizing decision circuit 46 decides the seizing of the 
exclusive transmission right because the non-permission signal NPS is not 
yet stored in the register 47, and produces the seizing signal SS. The 
transmission controller 36 produces the abort control signal ACS because 
no communication data are stored in the first data storage 35. Thus, the 
abort signal sender 38 operates so that the station 20 sends out the abort 
signal S (FIG. 3) to the transmission path 26 at a time t.sub.0 in FIG. 6 
(step 103 in FIG. 5). 
The abort signal S includes an address number "0" preassigned to the 
station 20 as the specific or source station number SA. 
The abort signal S on the transmission path 26 is detected by the abort 
signal detector 41 in each station 20-24 (for station 20, step 103 and for 
stations 21-24, step 104 in FIG. 5). In each station, the abort signal 
detector 41 produces the abort detection signal ADS when the 
synchronization information SYN in the abort signal S is detected. 
Subsequently, the abort signal detector 41 extracts the specific station 
number or the source address SA in the abort signal S and delivers the 
specific station number SA (=0) to the time calculator 44. 
The time calculator 44 calculates the waiting time period T.sub.1 given by 
equation (2), which is set in the timer 45 (step 105 in FIG. 5) at a time 
t.sub.1 in FIG. 6. In this case, the waiting time periods T.sub.1 (20), 
T.sub.1 (21), T.sub.1 (22), T.sub.1 (23), and T.sub.1 (24) in stations 20 
to 24 are 5t, t, 2t, 3t, and 4t, respectively, because the specific 
station number SA and the number W of the stations are "0" and "5", 
respectively, as mentioned before. 
Then, the timer 45 in station 21 generates the enabling signal ES before 
timers in other stations provide the enabling signals (step 106 in FIG. 
5), because the station 21 has the shortest waiting time period T.sub.1 
(21)=t at this stage, as described above. Accordingly, the seizing 
decision circuit 46 in the station 21 decides the seizing of the exclusive 
transmission right because the register 48 has not yet stored the 
non-permission signal NPS. Then, the transmission controller 36 in station 
21 checks whether the communication data to be transmitted are present or 
absent in the first data storage 35 (step 107 in FIG. 5). In this case, 
since it is assumed that no communication data are in the first data unit 
35, the transmission controller 36 produces the abort control signal ACS 
so that the abort signal sender 38 sends out the abort signal S through 
the transmitter 31 to the transmission path 26 (step 103 in FIG. 5). 
Thus, the station 21 sends out the abort signal S at time t.sub.2 after the 
unit time t from the time t.sub.1 as shown at 10.sub.1 in FIG. 6. The 
abort signal S includes, as the specific station number or the source 
address SA, the station number "1" assigned to the station 21. 
In each station 20-24, the abort signal S on the transmission path 26 is 
detected by the abort signal detector 41 (for station 21, step 103, for 
stations 20, 22-24, step 108 in FIG. 5), and the waiting time period 
T.sub.1 is newly calculated at the time calculator 44 and set to the timer 
45 at a time t.sub.3 in FIG. 6 (step 105 in FIG. 5), in the similar manner 
as described above. 
In this case, the waiting time periods T.sub.1 (20), T.sub.1 (21), T.sub.1 
(22), T.sub.1 (23), and T.sub.1 (24) in stations 20-24 are 4t, 5t, t, 2t, 
and 3t, respectively, because the specific station number SA and the 
number W of the total stations are equal to "1" and "5", respectively. 
Accordingly, at a time after the unit time t from the time instant t.sub.3, 
the station 22 sends out the abort signal S as shown at 10.sub.2 in FIG. 6 
(step 103 after passing through steps 106 and 107 in FIG. 5), and the 
waiting time period T.sub.1 is again newly calculated and set in the timer 
45 in each station of 20-24, in the similar manner as described above. 
Thereafter, the abort signal S is sequentially sent out to the transmission 
path 26 from stations 23, 24, 20, 21 and 22 one after another as shown in 
FIG. 6 in the similar manner as described above. 
Now, description will be made as to a case where communication data are 
stored in the first data storage 35 in one of stations 20-24, for example, 
in the station 22, with reference to FIGS. 1, 2, 5, and 7. 
As described above in connection with no communication data in each 
station, when the timer 45 in the station 22 produces the enabling signal 
ES and when the seizing decision circuit 46 produces the seizing signal 
SS, the abort signal S is sent out at a time t.sub.4 as shown at 10.sub.2 
in FIG. 6. However, when the transmission controller 36 detects (step 107 
in FIG. 5) that communication data are stored in the first data storage 
35, the transmission controller 36 produces not the abort control signal 
ACS but the data transmitting control signal TCS. 
In response to the data transmitting control signal TCS, the paging signal 
generator 37 sends out the paging signal E (FIG. 2) through the 
transmitter 31 to the transmission path 26 as shown at 10.sub.2 in FIG. 7 
(step 109 in FIG. 5). 
In the example being illustrated, it will be assumed that the paging signal 
E has, as the destination address DA, the station number, for example, "3" 
preassigned to the station 23 to which the communication data should be 
transferred from the station 22. In addition, the paging signal E has, as 
specific or source address SA, the preassigned station number N=2 assigned 
to the station 22. 
After completion of transmission of the paging signal E, the transmission 
controller 36 accesses the first data storage 35 to send out the 
communication data onto the transmission path 26 through the transmitter 
31 at a time instant t.sub.5 in FIG. 7 (step 111 in FIG. 5). 
The paging signal E on the transmission path 26 is detected by the paging 
signal detector 42 through the receiver 32 in each station of 20-24 (for 
station 22, step 109, for stations 20, 21, 23, and 24, step 110 in FIG. 
5). The paging signal detector 42 in each station of 20-24 produces the 
paging detecting signal PDS representative of the enquiry code ENQ when 
the enquiry information ENQ in the paging signal E is detected. The paging 
detecting signal PDS is supplied to the reception controller 40. 
Subsequently, the paging signal detector 42 extracts the destination 
address DA in the paging signal E as detected and delivers the extracted 
destination address DA to the coincidence detector 48. 
When the paging signal detector 42 further detects the sender or specific 
address SA in the paging signal E as received, it compares the specific 
address SA with the preassigned address N assigned to its own station at 
the station number comparator 42a. 
In the described example, the station number comparator 42a in the station 
22 detects that the specific address SA (=2) coincides with the 
preassigned station number N (=2). In each of the other stations 20, 21, 
23, and 24, the station number comparator 42a produces the non-permission 
signal NPS to the register 47 since the specific address SA is not 
coincident with the preassigned station number N. Accordingly, each of the 
stations 20, 21, 23, and 24 cannot seize the exclusive transmission right 
even if the timer 45 produces the enabling signal ES thereafter. However, 
the register 47 is rewritten by the enabling signal ES from the 
non-permission state to the permission. 
The coincidence detector 48 receives the destination address DA extracted 
by the paging signal detector 42 and detects coincidence of the received 
destination address DA and the preassigned station number N assigned to 
its own station (step 113 in FIG. 5). 
In the present assumption, the coincidence detector 48 in the station 23 
having a station address "3" produces the coincidence signal CS because 
the destination address DA is "3" as mentioned before. As a result, the 
reception controller 40 in the station 23 produces the reception control 
signal RCS to the second data storage 39 which stores the communication 
data received by the receiver 32 (step 114 in FIG. 5). 
On the other hand, the coincidence detector 48 in each station of 20, 21, 
22, and 24 except station 23 does not detect the coincidence. Accordingly, 
the reception controller 40 in each station of 20-22 and 24 does not 
operate. 
Thus, transmission of the communication data from the station 22 to the 
station 23 is carried out. Then, each other station of 20, 21, and 24 is 
placed in a waiting step (115 in FIG. 5) for a fresh one of the abort 
signal S. 
As mentioned above, the exclusive transmission right is not seized by the 
stations 20, 21, 23, and 24 except the station 22 which already seizes the 
exclusive transmission right and the single station 22 only can transmit 
the communication data. Therefore, it is possible to avoid contention for 
the exclusive transmission right between a plurality of stations. 
In the station 22 sending out the communication data, when the transmission 
of the communication data is completed at the time t.sub.6 as shown in 
FIG. 7 (step 112 in FIG. 5), the transmission controller 36 produces the 
abort control signal ACS to the abort signal sender 38. Then, the abort 
signal sender 38 sends out the abort signal S, which has the station 
number "2" as the specific station number SA, through the transmitter 31 
to the transmission path 26 at t.sub.6, as shown at 10.sub.2 in FIG. 7 
(step 103 in FIG. 5). 
The sent-out abort signal S on the transmission path 26 is detected by the 
abort signal detectors 41 through receiver 32 in all of the stations 20-24 
(for station 22, step 103, for stations 20, 21, and 24, step 115, and for 
station 23, step 116 in FIG. 5). 
In each station of 20-24, the abort signal detector 41 detects the 
synchronization information SYN in the abort signal S to produce the abort 
detecting signal ADS and, then, extracts the specific address or source 
address SA which is supplied to the time calculator 44. Subsequent 
operation is made in the manner similar to the above-mentioned operation. 
In the example shown in FIG. 7, the station 20 transmits the paging signal 
E and the communication data when it seizes the exclusive transmission 
right. 
In the embodiment, when the station, for example, 22 having the exclusive 
transmission right suffers from any fault after transmission of the paging 
signal E so that it cannot send out the abort signal S, any one of the 
other stations 20, 21, 23, and 24 cannot seize the exclusive transmission 
right and the network system is disadvantageously maintained in the 
non-operation condition. 
Such a disadvantage can be avoided in another embodiment as shown in FIG. 
8. 
Referring to FIG. 8, the illustrated station according to another 
embodiment of the present invention is similar to that illustrated in FIG. 
4 except for a signal monitor 50 and seizing control circuit portions 
accompanying thereto. The seizing control unit is, therefore, depicted at 
not 43 but 43a. The similar circuit portions are represented by the same 
reference numerals as in FIG. 4 and are not described in detail for the 
purpose of simplification of the description. 
The signal monitor 50 is coupled with the receiver 32. 
In the embodiment, the coincidence detector 48a is different from the 
coincidence detector 48 in FIG. 4 in that it produces a non-coincidence 
signal NCS when the coincidence is not detected. The non-coincidence 
signal NCS is applied to the signal monitor 50. 
When receiving the non-coincidence signal NCS, the signal monitor 50 starts 
the monitoring operation for detecting any signal received from the 
transmission path 26 through the receiver 32. The signal monitor 50 
produces a monitored signal MS when any signal is present. The signal 
monitor 50 stops the monitoring operation in response to the abort 
detection signal ADS from the abort signal detector 41. 
The seizing control unit 43a a is provided with a time generator 51 and 
another timer 52 similar to the timer 45. Those timers 45 and 52 will be 
referred to as first timer and second timer, hereinafter. 
In response to the monitored signal MS, the time generator 51 produces 
another waiting time period T.sub.2 determined dependent on the 
preassigned station number N as will later be described. The waiting time 
periods T.sub.1 and T.sub.2 from the time calculator 44 and the time 
generator 51 will be referred to as the first and second waiting time 
periods, respectively, hereinafter. 
The second waiting time period T.sub.2 is defined by the following equation 
(3); 
EQU T.sub.2 =(W+N).times.t (3). 
The second waiting time period T.sub.2 is set in the second timer 52. The 
second timer 52 starts the time measuring operation in response to setting 
of the second waiting time period T.sub.2 and produces another enabling 
signal when the measured time period becomes equal to the second waiting 
time period T.sub.2 set in the second timer 52. 
The enabling signal provided from the first timer 45 will be called the 
first enabling signal ES.sub.1, while the enabling signal from the second 
timer 52 will be referred to as the second enabling signal ES.sub.2. 
The second enabling signal ES.sub.2 is applied to the seizing decision 
circuit 46 through an OR gate 53. The first enabling signal ES.sub.1 from 
the first timer 45 is also applied to the seizing decision circuit 46 
through the OR gate 53. Furthermore, the seizing decision circuit 46 
produces the seizing signal SS also when receiving the second enabling 
signal ES.sub.2. 
Operation of the bus-method communication network system of FIG. 1 using 
the station arrangement of FIG. 8 will be described below with reference 
to FIGS. 9 and 10. 
The flow chart in FIG. 9 is similar to the flow chart in FIG. 5 except for 
steps 117-121 which are added in place of step 115 in FIG. 5 due to 
addition of the signal monitor 50, the time generator 51, and the second 
timer 52 in the embodiment of FIG. 8. The similar steps are represented by 
the same reference numerals in FIG. 5. 
In case that any communication data to be trassmitted are absent in all of 
the stations 20-24, operation of the system is similar to that illustrated 
in FIG. 6 and therefore, its description is omitted. In case that the 
communication data to be transmitted to, for example, station 23 are 
present in any one of the stations, for example, station 22, operation is 
also similar to that illustrated in FIG. 7 if no fault occurs in the 
station 22 after the station 22 transmits the paging signal E and if the 
station 22 sends out the abort signal S after completion of transmission 
of the communication data. 
Referring to FIG. 10, when the paging signal E is sent out from the station 
22 onto the transmission path 26 (step 109 in FIG. 9) at a time t.sub.4 
similar to the example in FIG. 7, the paging signal E is detected by the 
paging signal detector 41 in each of stations 20, 21, 23, and 24 (step 110 
in FIGS. 5 and 9), as described above. Then, the coincidence detector 48a 
in the station 23 produces the coincidence signal CS but the coincidence 
detector 48a in each of the other stations 20, 21, and 24 produces the 
non-coincidence signal NCS (step 113 in FIG. 9). This is because the 
coincidence between the destination address DA and the preassigned station 
number N is not detected by the coincidence detector 48a in the stations 
20, 21, and 24. Responsive to the non-coincidence signal NCS, the signal 
monitor 50 in each station of 20, 21, and 24 starts the monitoring 
operation and produces a monitored signal MS. In response to monitored 
signal MS, the time generator 51 generates the second waiting time period 
T.sub.2 given by equation (3) at the time t.sub.5 as shown in FIG. 10. The 
time t.sub.5 is earlier than that time when the timer 45 in each station 
of 20, 21, and 24 will produce the first enabling signal ES.sub.1. The 
second waiting time periods T.sub.2 (20), T.sub.2 (21), and T.sub.2 (24) 
of the stations 20, 21, and 24 are 5t, 6t, and 9t, respectively. This is 
because the stations 20, 21, and 24 have the preassigned station numbers 
of "0", "1", and "4", respectively, and the number of stations W is "5". 
In each station of 20, 21, and 24, the second waiting time period T.sub.2 
is set in the second timer 52 (step 117 in FIG. 9). Thereafter, the signal 
monitor 50 continues the signal monitoring operation (step 121 in FIG. 9). 
The signal monitor 50 also produces the monitored signal MS when any 
signal is present. 
In response to the monitored signal, the time generator 51 again generates 
the second waiting time period T.sub.2, which is again set into the second 
timer 52 (step 117 in FIG. 9). Therefore, the timers 52 in each station of 
20, 21, and 24 are repeatedly set to the second waiting time period 
T.sub.2 as long as any signal presents on the transmission path 26. 
Thereafter, when the station 22 has no fault and finally sends out the 
abort signal S, the abort signal S is detected at each station of 20-24 
(for stations 20, 21, and 24, step 120, for station 23, step 116, and for 
station 22, step 103 in FIG. 9), the operation normally continues as 
described before in connection with FIG. 5. 
However, when any fault occurs at the station 22 and no signal is sent out 
to the transmission path 26 at t.sub.6 in FIG. 10, the signal monitor 50 
in each station of 20, 21 and 24 stops the monitored signal. 
Therefore, the second timer 52 is not again set to the second waiting time 
period T.sub.2 but produces the second enabling signal ES.sub.2 when the 
second waiting time period T.sub.2 elapses thereafter. Then, the timer 52 
in the station 20 firstly produces the second enabling signal ES.sub.2 
earlier than the other stations because the station 20 has the shortest 
second waiting time period T.sub.2 (=5t). 
When the second enabling signal ES.sub.2 is produced in station 20 (step 
118 in FIG. 9), the seizing decision circuit 46 produces the seizing 
signal SS. Under the above-described control manner of the transmission 
controller 36 responsive to the seizing signal SS, the abort signal S is 
sent out from the station 20 (step 103 in FIG. 9) as shown at 10.sub.0 in 
FIG. 10, if there are no communication data to be transmitted (step 119 in 
FIG. 9). Alternatively, the paging signal E and the communication data are 
sent out from the station 20 (steps 119, 109, and 111 in FIG. 9) if there 
are communication data, and the abort signal S follows the communication 
data (step 103 in FIG. 9). 
Thus, the operation of the network system continues thereafter with the 
faulty station 22 being omitted. 
It is assumed in the above description that fault occurs in the station 22, 
but it will be noted that the network system is continued operative in the 
similar manner if fault occurs in the other one of stations or even in 
several ones of the stations. 
In FIG. 8, although two separate timers 45 and 52 are used, it will be 
understood from the above-described operation that they can be replaced by 
a single timer. 
Referring to FIG. 11, a single timer 55 is a similar one as timers 45 and 
51. The timer 55 is coupled to the time calculator 44 and the time 
generator 51 so that when either one of the initial and first time periods 
T.sub.0 and T.sub.1 and the second time period T.sub.2 is supplied to the 
single timer 55, it is freshly set in the timer 55 with the previously set 
time period being cancelled. 
The timer 55 supplies the enabling signal ES to a seizing decision circuit 
56 similar to 46 in FIG. 4, when the last set time period elapses. The 
seizing decision circuit 56 produces the seizing signal SS in response to 
the enabling signal ES. 
The seizing decision circuit 56 needs not have the register 47 which is 
used in the embodiment in FIG. 8, because the second time period T.sub.2 
is freshly set in the timer 55 when the paging signal E is detected so 
that the enabling signal production of the timer 55 is prolonged until the 
second time period T.sub.2 elapses or until a fresh one of the first time 
period T.sub.1 calculated in response to incoming of the next subsequent 
abort signal elapses. 
Referring to FIG. 12, the illustrated station according to another 
embodiment of the present invention is similar to that illustrated in FIG. 
4 except for a timer 60 and other portions accompanying thereto. 
The similar portions are represented by the same reference numerals as in 
FIG. 4 and the detailed description thereto is omitted. 
A seizing control unit 43b is different from the unit 43 in FIG. 4 and has 
the timer 60, an RS flipflop 61, an AND gate 62, and an OR gate 63 which 
are added into the seizing control unit 43 in FIG. 4. 
A transmission controller 36a is different from the transmission controller 
36 in FIG. 4 in that the transmission controller 36a does not produce the 
abort control signal ACS immediately when checking no data in the first 
data storage 35 in response to the seizing signal SS from the seizing 
decision circuit 46 but sets another waiting time period T.sub.3 in the 
timer 60. The timer 60 will be called the third timer and the time period 
T.sub.3 will be called the third waiting time period, hereinafter. 
The transmission controller 36a in the station 20 having the smallest 
station number "0" has a flipflop 201 which is set by the power-on signal. 
When the flipflop 201 is set, the transmission controller 36a produces the 
abort control signal ACS immediately when receiving the seizing signal SS. 
Then, the flipflop 201 is reset by the seizing signal SS without setting 
the timer 60. Thereafter, the transmission controller 36a sets the timer 
60 when checking no data in the first data storage 35 in response to the 
seizing signal SS. 
The transmission controller 36a in each of the other stations 21-24 does 
not have such a flipflop. 
The third waiting time period T.sub.3 is not dependent on the station 
number but is constant for all of the stations. The third waiting time 
period T.sub.3 is determined by the following equation (4); 
EQU T.sub.3 =W.times.t (4). 
The third timer 60 may be a presetable counter type similar to the first 
timer 45 and may be a fixed type having a fixed operation time period 
equal to T.sub.3. In use of the presetable type, the third waiting time 
period T.sub.3 is previously set into the timer. Even if either one of the 
two types is used, the transmission controller 36a applies only a start 
signal in response to the seizing signal SS to the timer 60, whereby the 
timer 60 operates time measuring and produces a timer output signal when 
the third waiting time T.sub.3 elapses. The timer output signal is applied 
to the transmission controller 36a when the AND gate 62 is open. 
In response to the timer output, the transmission controller 36a again 
checks the content of the first data storage 35 and produces abort control 
signal ACS when communication data to be transmitted are absent. 
The transmission controller 36a applies the start signal to a set input 
terminal (s) of the RS flipflop 61 and sets the flipflop 61. A set output 
terminal (T) of the flipflop 61 is coupled to one input terminal of the 
AND gate 62. The timer output signal is applied to the other input 
terminal of the AND gate 62. An output terminal of the AND gate 62 is 
connected to the transmission controller 36a. Accordingly, the timer 
output signal is applied to the transmission controller 36a only when the 
flipflop 61 is in a set condition. 
To a reset input terminal (R) of the flipflop 61, the abort detection 
signal ADS and the non-permission signal NPS are applied from the abort 
signal detector 41 and the paging signal detector 42, respectively, 
through the OR gate 63. Accordingly, when the abort signal S or the paging 
signal E is detected in the station during operation of the timer 60, the 
flipflop 61 is reset and the AND gate 62, thereafter, blocks the timer 
output signal. 
In case that the first data storage 35 hasaany communication data to be 
transmitted, the transmitter controller 36a responsive to the timer output 
signal operates in the similar manner as the transmission controller 36 in 
FIG. 4. 
Now, referring to FIGS. 13-16, description will be made as to operation of 
the bus-method communication network system using the station arrangement 
shown in FIG. 12 for each station. 
In FIG. 13, the similar steps are represented by the same reference 
numerals as in FIG. 5. It will be noted from comparison with FIG. 5 that 
steps 122-125 are added in the flow chart in FIG. 5. Further, step 108 is 
branched off from not step 106 but step 123 and a new step 125 is branched 
off from step 106. It will be understood from the above description that 
these differences are due to operation of the third timer 60 and the 
transmission controller 36a. 
When the bus-method communication network system starts, power-on signal is 
applied to the time calculator 44 in each station of 20-24 and to the 
flipflop 201 in the station 20. Thereafter, the station 20 at first sends 
out the abort signal S to the transmission path 26 (steps 101-103 in FIG. 
13) in the manner as described above in connection with the embodiment of 
FIG. 4 because the station 20 has the station number of N=0 and the 
flipflop 201 is set. 
The flipflop 201 may not be omitted in the station 20. In that case, it 
takes longer time by the third waiting time period T.sub.3 (step 123 in 
FIG. 13) in comparison with the embodiment of FIG. 4 until the station 20 
sends out the abort signal S after start of the system. 
In the station 20, the abort signal S is received (step 103 in FIG. 13) and 
the first waiting time period T.sub.1 (=5t) is set in the first timer 45 
as shown at 10.sub.0 in FIG. 14 (step 105 in FIG. 13) in the similar 
manner as the embodiment of FIG. 4. 
In each of the other stations of 21-24, the abort signal S sent out from 
the station 20 is detected and the first waiting time period T.sub.1 
(T.sub.1 (21)=t, T.sub.1 (22)=2t, T.sub.1 (23)=3t, and T.sub.1 (24)=4t) is 
set in the timer 45 of each station (steps 104 and 105 in FIG. 13) at 
t.sub.1 in FIGS. 14-16 in the similar manner as the embodiment in FIG. 4. 
Then, the enabling signal ES is produced from the timer 45 in the station 
21 after lapse of the time period T.sub.1 (21) and the seizing signal SS 
is produced from the seizing decision circuit 46 so that the transmission 
controller 36a checks the first data storage 35 (steps 106 and 107 in FIG. 
13). When the first data storage 35 has no communication data, the 
transmission controller 36a drives the third timer 60 at t.sub.2 in FIG. 
14 (step 122 in FIG. 13) without sending out the abort signal S as 
described above. Accordingly, each station of 20-24 is different from the 
embodiment of FIG. 4 and the first timer 45 in each station is not reset. 
Therefore, the first timer 45 in the station 22 next produces the enabling 
signal ES at a time instant t.sub.3 in FIG. 14 when the first waiting time 
period T.sub.1 (22) elapses after the time instant t.sub.1. When the 
station 22 has no communication data, the abort signal S is not 
transmitted from the station 22, too, and the third waiting time period 
T.sub.3 is also set in the third timer 60 in the station 22 (steps 106, 
107 and 122 in FIG. 13). 
In the similar manner, the timer 45 in each station of 23, 24, and 20 
produces sequentially the enabling signal ES when the first waiting time 
period T.sub.1 elapses after the time instant t.sub.1, but no abort signal 
S is sent out from each station of 23, 24, and 20 and the third timer 60 
in each station is set to the third waiting time period T.sub.3, as shown 
at 10.sub.3, 10.sub.4, and 10.sub.0 in FIG. 14, when the stations 23, 24, 
and 20 have no communication data. 
Thereafter, the third timer 60 in the station 21 produces the timer output 
signal at a time instant t.sub.4 in FIG. 14 after the third waiting time 
period T.sub.3 (=5t) from the time instant t.sub.2. In response to the 
timer output signal, the station 21 sends out the abort signal S (steps 
123, 124, and 103 in FIG. 13) as shown at 10.sub.1 in FIG. 14. 
In response to the abort signal S sent out from the station 21, the timer 
45 is set (for station 21, steps 103 and 105, for stations 20 and 22-24, 
steps 108 and 105 in FIG. 13) in each station 20-24 at a time instant 
t.sub.5 in FIG. 14. 
Thereafter, the similar operation as described above is repeated in the 
network system as long as all of the stations 20-24 have no communication 
data, while the station sending out abort signal S shifts from one station 
after another in the order of the station number with the time interval of 
6t (T.sub.3 +t), as shown in FIG. 14. 
Assuming that one station, for example, station 22 has communication data 
when its transmission controller 36a checks the first data storage 35 in 
response to the seizing signal SS (step 107 in FIG. 13), the transmission 
controller 36a produces the transmission control signal TCS at a time 
instant t.sub.3 in FIG. 15. Then, the paging signal E and the 
communication data following the abort signal S are sequentially sent out 
from the station 22 (steps 109, 111, 112, and 103 in FIG. 13) as shown at 
10.sub.2 in FIG. 15 in the similar manner as described above in connection 
with the embodiment of FIG. 4. 
The paging signal E is detected at the other stations 20, 21, 23, and 24 
(for stations 20 and 21, step 110, and for stations 23 and 24, step 125 in 
FIG. 13). Thereafter, the stations 20-24 operate (step 113, 115, 114, and 
116) in the fashion similar to the operation of the stations in the 
embodiment of FIG. 4, until the abort signal S is sent out from the 
station 22 at a time instant T.sub.6 in FIG. 15. In response to the abort 
signal S, the timer 45 in each station of 20-24 is set to the first 
waiting time period T.sub.1 at the step 105 in FIG. 13, as shown at a time 
instant t.sub.7 in FIG. 15. 
In the example shown in FIG. 15, the station 21 is shown to have 
communication data when the seizing decision circuit 46 in the station 21 
produces the seizing signal SS at a time instant t.sub.8 in FIG. 15 after 
the time duration T.sub.1 (21) (=4t) from the time instant t.sub.7. 
In a case where no paging signal E is sent out from any one of the stations 
20-24 after the third timer 60 in one of stations 20-24, for example, 
station 21 starts at the time instant t.sub.2 in FIG. 16, the timer output 
signal of the third timer 60 is received at the transmission controller 
36a in the station 21 at the time instant t.sub.4 in FIG. 16 (step 123 in 
FIG. 13), as described in connection with FIG. 14. Then, the transmitter 
controller 36a again accesses the first data storage 35 (step 124 in FIG. 
13). When the first data storage 35 has communication data, the 
transmission controller 36a controls the paging signal generator 37 and 
the first data storage 35 to send out the paging signal E and the 
communication data from the station (steps 109 and 111 in FIG. 13) as 
shown at 101 in FIG. 16. Then, the abort signal S is sent out when the 
transmission of the communication data is completed (steps 112 and 103 in 
FIG. 13), as shown at 10.sub.1 in FIG. 16. In response to the abort signal 
S, the first timer 45 in each station is set to the first waiting time 
period T.sub.1 at a time instant t.sub.9 in FIG. 16 (step 105 in FIG. 13). 
In the example shown in FIG. 16, the station 22 next seizes the exclusive 
transmission right after the first waiting time period T.sub.1 (=t) 
elapses (step 106 in FIG. 13) and sends out the paging signal E, 
communication data, and the abort signal S to the transmission line 26 
(steps 107, 109, 111, 112, and 103 in FIG. 13) as shown at 10.sub.2 in 
FIG. 16. 
In this embodiment, shift of exclusive transmission right from one station 
having no communication data to another station can be faster than the 
embodiment of FIGS. 2 and 8 because the one station sends out no abort 
signal and the another station seizes the transmission right automatically 
when the first waiting time period elapses. In absence of communication 
data in all of the stations, the abort signal S is sent out from one 
station under control of the third timer 60 after the transmission right 
shifts from the one station and returns to the one station through the 
other stations sequentially. In presence of communication data, the abort 
signal S is also sent out after completion of transmission of the 
communication data. 
Each timer of 45 and 60 in each of the stations is synchronized with one 
another by the abort signal S. Thus, contention between different stations 
for the exclusive transmission right can be reliably avoided. 
FIG. 17 shows a further embodiment of a station used for each station of 
20-24 in the system in FIG. 1. The station in FIG. 17 comprises the 
arrangement of the station of FIG. 12 and is characterized by addition of 
a signal monitor 50, a time generator 51, a second timer 52, and an OR 
gate 53 which are similar to those represented by the same reference 
numerals in FIG. 8. Therefore, similar portions of the station are 
represented by the same reference numerals in FIGS. 8 and 12, and 
description thereto is omitted for the purpose of simplification. 
A seizing control unit 43c is different from that 43b in FIG. 12 by 
provision of the timer generator 51, the second timer 52, and the OR gate 
53. However, it should be noted that the second enabling signal ES.sub.2 
is also coupled with the transmission controller 36 to set the flipflop 
201. Therefore, after production of the second enabling signal ES.sub.2, 
the transmission controller 36a does not set the third timer 60 but 
produces the abort control signal ACS immediately when receiving the 
seizing signal SS in response to the second enabling signal ES.sub.2 if 
the first data storage 35 has no communication data. 
A flow chart of operation of a network system using the of stations FIG. 17 
for each station of 20-24 in FIG. 1 is shown in FIG. 18. The flow chart is 
similar to the flow chart in FIG. 13 except that the series of steps 
117-121 is added in place of step 115 in FIG. 13. The series of steps 
117-121 are similar to the series of steps 117-121 in FIG. 9. Therefore, 
the bus-method communication network system using the station of FIG. 17 
for each station of 20-24 in FIG. 1 operates in the similar manner as the 
system using the station of FIG. 12, as long as any fault does not occur 
in one of the stations seizing the exclusive transmission right after 
sending out the paging signal E. That is, when all of the stations 20-24 
have no communication data in their first data storages 35, the operation 
is similar to that shown in FIG. 14. When one of the stations 20-24, for 
example, station 22 has communication data at step 107, operation of the 
system is similar to that of FIG. 15. Further, one of the stations 20-24, 
for example, station 21 has communication data at step 124, the operation 
of the system is similar to that shown in FIG. 16. 
Referring to FIG. 19, operation of the system will be described as to a 
case where a fault occurs in one of the stations 20-21, for example, 
station 21 after sending out the paging signal E. 
When the station 20 sends out the abort signal S at a time t.sub.0 (step 
103 in FIG. 18), the station 21 detects the abort signal S at a time 
instant t.sub.1 (step 116, 108 or 120) and the first timer 45 in the 
station 21 is set to T.sub.1 (=t) at step 105. After lapse of T.sub.1 
(=t), the paging signal E is sent out from the station 21 as shown at 
10.sub.1 in FIG. 19 (step 109 in FIG. 18) when the first data storage 35 
has communication data (step 107 in FIG. 18). Thereafter, the 
communication data are sent out from the station 21 (step 111 in FIG. 18), 
as shown at 10.sub.1 in FIG. 19. When a fault occurs in the station 21 
during sending out the communication data and when no signal, therefore, 
is on the transmission path 26 thereafter, setting operation (steps 121 
and 117) of the second timer 52 in all of the stations is stopped because 
the time generator 51 is not actuated by the signal monitor 50. 
Thereafter, the second timer 52 in station 20 having the smallest station 
number "0" times up (at step 118 in FIG. 18) and produces the second 
enabling signal ES.sub.2. In response to the second enabling signal 
ES.sub.2, the flipflop 201 is set and the seizing decision circuit 46 
produces the seizing signal SS. Then, the transmission controller 36a 
produces the abort signal ACS when the first data storage 35 of the 
station 20 has no communication data (step 119 in FIG. 18). At the same 
time, the flipflop 201 is reset. Then, the abort signal S is sent out from 
the station 20 as shown at 10.sub.1 in FIG. 19 (step 103 in FIG. 18). 
Thereafter, the first timer 45 is set (step 105 in FIG. 18) in each 
station 20-24 except faulty station 21. It is of course true that when the 
first data storage 35 has communication data, the transmission controller 
36a produces the transmission control signal TCS so that the paging signal 
E, the communication data, and the abort signal S are sequentially 
transmitted to the transmission path 26 (steps 119, 109, 111, 112, and 103 
in FIG. 18). Therefore, the system continuously operates without station 
21. 
In the above description of FIG. 17, the second enabling signal ES.sub.2 is 
also necessary to set the flipflop 201 by the second enabling signal 
ES.sub.2. In that case, operation progresses from the step 119 to step 122 
when the first data storage 35 has no communication data. Therefore, 
transmission of the abort signal S is delayed by the third waiting time 
period T.sub.3. 
The first timer 45 and the second timer 52 can be replaced by a single 
timer in the similar manner as shown in FIG. 11.