JPH0362335B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a LAN (local area network) system in which a plurality of terminals are connected to one transmission path.

[Conventional technology]

Conventionally, in this type of LAN system, as shown in FIG. 9, a plurality of terminals _10'0 to 10'o _-1 and a master controller 40 are connected to a serial data bus 30, and each terminal has a has an output device. Each terminal exchanged data with the master controller, and a series of processes from input to output were processed within each terminal.

[Problem that the invention seeks to solve]

Conventional LAN systems require a master controller separate from the terminals, which has the disadvantage of complicating the overall system configuration. Furthermore, since each terminal needed to have both an input device such as a keyboard and an output device such as a printer or display, there was a drawback that the terminal became large. Furthermore, since data is exchanged between terminals via a master controller, there is also the drawback that it takes time to exchange data.

[Means and actions for solving problems]

By sharing output devices such as printers and displays, the LAN system according to the present invention reduces the size of each terminal, eliminates the need for a master controller, and allows data to be exchanged between terminals in a short time. It is characterized by

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of a LAN system according to the present invention. In this embodiment, three data input terminals 10 ₀ , 10 ₁ , 10
₂ and two data output terminals 20 ₀ and 20 ₁ are connected to the serial data bus 30.

The data input terminal 10 includes a bus transceiver 11 for transmitting and receiving signals on the serial data bus 30, a setting switch 12 such as a dip switch for setting a terminal number, an input device 13 for inputting data, and a timer value. It is composed of a timer 14 to be set, a memory 15 having a program and a work area, and a control device 16 consisting of a microprocessor, and the control device 16 controls the bus transceiver 11, input device 13, timer 14, and memory 15. . The input device 13 may be a keyboard, a fixed scanner, or the like.

Similarly, the data output terminal 20 includes a bus transceiver 21 for transmitting and receiving signals on the serial data bus 30, a setting switch 22 for setting the terminal number, an output device 23 for outputting data, and a timer value. It is composed of a timer 24 to be set, a memory 25 having a program and a work area, and a control device 26 consisting of a microprocessor.
1. Controls the output device 23, timer 24 and memory 25. In this embodiment, it is assumed that the output devices 23 of the terminals 20 ₀ and 20 ₁ are a display and a printer, respectively.

The terminal numbers set by the setting switch 12 or 22 for each terminal 10 ₀ , 10 ₁ , 10 ₂ , 20 ₀ and 20 ₁ are "0", "1", "2", "3" and "4", respectively. ” is assigned.

Figure 2 shows each data input terminal 1 shown in Figure 1.
0 is a block diagram showing a specific configuration example of
The control device 16 is shown divided into blocks according to function.

The bus transceiver 11 includes a parallel/serial converter (hereinafter abbreviated as P/S converter) 11 _-1 for converting parallel data from the control device 16 into serial data and sending it onto the serial data bus 30. and a serial /
Parallel converter (hereinafter abbreviated as S/P converter) 1
1 _-2 . Also, the P/S converter 11 _-1
The S/P converter 11-2 also has a function of converting a logical code into a transmission code, and the S/P converter _11-2 also has a function of converting a transmission code into a logical code. In this embodiment, it is assumed that the parallel data is 8 bits.

The memory 15 includes a transmission data storage area 15 _-1 for temporarily storing transmission data and a reception data storage area 15 _-2 for temporarily storing reception data.
It has Of course, although not shown, the memory 15 also has an area for storing programs.

In the control device 16, _16-1 is a terminal number holding section for holding the own terminal signal set by the setting switch 12. _16-2 is a synchronization signal sending unit for sending out a synchronization signal, which will be described later.
_16-3 is a calling signal sending unit for sending out a calling signal, which will be described later. _16-4 is a response signal sending unit for sending out a response signal, which will be described later.
_16-5 is a synchronization signal detection unit for detecting a synchronization signal. 16 _-6 is a calling signal detection unit for detecting a calling signal. _16-7 is a response signal detection unit for detecting a response signal. 16 _-8
is a timer setting unit for setting a timer value to the timer 14, which will be described later. _16-9 is a transmission/reception control unit for controlling transmission and reception of signals, as will be described later. _16-10 is a signal monitoring unit for monitoring whether or not there is a signal on the serial data bus 30. Note that the transmission/reception control unit 16 _-9 is connected to the input device 13
It also has a function of storing data input from the memory 15 in the transmission data storage area 15 _-1 of the memory 15 as transmission data.

Figure 3 shows each data output terminal 2 shown in Figure 1.
FIG.
The difference from FIG. 2 is that an output device 23 is connected instead of the input device 13. The transmission/reception control section 26 _-9 also has a function of outputting the received data temporarily stored in the received data storage area 25 _-2 of the memory 25 to the output device 23 as output data.

FIGS. 4a and 4b are flowcharts for explaining the operations of the data input terminal 10 and the data output terminal 20 shown in FIG. 1. Also, the fifth
6, 7 and 8 are time charts for explaining the operation of this embodiment. below,
The operation will be explained with reference to these figures.

FIG. 5 shows an example where there is no data to be sent by the data input terminal 10 and the data output terminal 20. First, when the power switch (not shown) _{of the} system shown in _FIG . _-1 and 26 The timer value T ₀ corresponding to the own terminal number N held in _-1 is set in the timers 14 and 24 (step 101). Here, if the basic unit of the timers 14 and 24 is τ, the timer value T ₀ is expressed by the following equation.

T ₀ = (N+1)×τ ...(1) Therefore, data terminals 10 ₀ , 10 ₁ , 10 ₂ , 2
The timer values T ₀ of 0 ₀ and 20 ₁ are respectively τ,
2τ, 3τ, 4τ and 5τ.

At data input terminal 10 ₀ , its timer 14
When timer 1 times up at time t ₁ , which is a time τ elapsed from time t ₀ (YES in step 102), the timer 1
4 outputs a time-up signal to the transmission/reception control section _16-9 . Upon receiving the time-up signal, the transmission/reception control section _16-9 activates the synchronization signal transmission section _16-2 to transmit the synchronization signal _Sy to the serial data bus 30 via the P/S conversion section _11-1 (step 103).
Here, the synchronization signal S _y is a synchronization field including synchronization information SYN, own terminal number (sender address)
Address field including SA and check code
Consists of check fields including BCC. Therefore, the data input terminal ₁₀₀ sends "0" as its own terminal number SA. This own terminal number is sent in advance from the terminal number holding section _16-1 to the synchronization signal sending section _16-2 by the transmission/reception control section _16-9 .
Stored.

This sent synchronization signal S _y is transmitted to each data terminal 1.
0 and 20, they are detected by the synchronization signal detection units _16-5 and _26-5 via the S/P conversion units _11-2 and _21-2 (YES in steps 103 and 104). The synchronization signal detection units _16-5 and _26-5 first detect the synchronization signal SYN in the synchronization signal _Sy , so that
Outputs the synchronization signal detection signal, and then outputs the synchronization signal S _y
Extracts the source address SA included in the address field in the timer setting sections _16-8 and 26.
Output to _-8 . The timer setting units 16 _-8 and 26 _-8 set the timer value based on the received source address SA and the own terminal number N held in the terminal number holding units 16 _-1 and 26 _-1 . Set T ₁ to timers 14 and 24 at time t ₂ (step
105).

Here, the timer value _T1 is expressed by the following equation, where W is the total number of data terminals connected to the serial data bus 30.

T ₁ ={mod _W (N-SA+W-1)+1}×τ (2) Here, mod _W (X) represents the remainder when X is divided by W. Therefore, in other words, (2)
The equation can also be expressed as the following equation.

T ₁ = (N-SA)×τ (When N>SA) = (N-SA+W)×τ (When N≦SA) ...(2) In this case, SA="0", W=" 5”, so
Data terminals 10 ₀ , 10 ₁ , 10 ₂ , 20 ₀ and 20 ₁
The timer values _T1 are 5τ, τ, 2τ, 3τ and
It becomes 4τ.

In the data input terminal 10 ₁ , the timer 14
At time _t3 , when time τ has elapsed since time _t2 , the time-up occurs (YES in step 106), and a time-up signal is output to the transmission/reception control section _16-9 . When the transmission/reception control unit _16-9 receives this time-up signal, it acquires the transmission right and determines whether there is any data to be transmitted (step 107). In this case, it is assumed that there is no data to be sent from all data terminals, so the transmission/reception control section _16-9
Inform _-8 of that fact (information that there is no data to send). Upon receiving this information, the timer setting unit _16-8 sets a predetermined timer value _T2 in the timer 14 (step 108).

Here, the timer value T ₂ is expressed by the following equation.

T ₂ = W × τ ... (3) On the other hand, at other data terminals 10 ₂ , 20 ₀ , 20 ₁ and 10 ₀ , the data from time t ₂ to 2τ, 3τ,
The transmission right is acquired at the time when 4τ and 5τ have elapsed, and since there is no data to be transmitted, the timer value T ₂ is set in the timers 14 and 24.

Next, in the data input terminal ₁₀₁ , the timer 14 times up at time _t4 , which is 5τ after time _t3 (YES in step 109), and the transmission/reception control unit _16-9 issues the transmission right. is acquired, but there is no data to be sent (step 110).
(NO), the process returns to step 103 and the synchronization signal sending section 1
6. Start _-2 and send out the synchronization signal S _y .

In each data terminal, the synchronization signal S _y is detected by the synchronization signal detection units 16 _-5 and 26 _-5 (YES in step 103 and step 111), and as described above,
The timer setting units _16-8 and _26-8 set the timer value _T1 in the timers 14 and 24 at time _t5 (step 105). At this time, data terminals 10 ₀ , 10
The timer values T ₁ of ₁ , 10 ₂ , 20 ₀ and 20 ₁ are 4τ, 5τ, τ, 2τ and 3τ, respectively. Therefore, the data terminal whose timer will time up first this time is 10 ₂ .

By repeating the above operations, synchronization signals are sequentially transmitted on the serial data bus 30 in the order of data terminals with the smallest terminal number, then data terminals with the largest terminal number, then data terminals with the smallest terminal number, and so on. S _y is sent at a predetermined period.

FIGS. 6 and 7 show an example where there is data to be sent to a data terminal.

First, referring to FIG. 6, when the power is turned on at time _t0 , a timer value T0 is set in the timers 14 and 24 of each data terminal (step 101), and the timer value _T0 is set in the timers 14 and 24 of each data terminal.
The data input terminal ₁₀₀ , which timed up for the first time at time _t1 when time τ has elapsed from time _t0 (YES in step 102), transmits the synchronization signal _Sy from the synchronization signal sending unit _16-2 onto the serial data bus 30. (step 103), and each data terminal transmits the synchronization signal to the synchronization signal detection section 16.
_-2 and 26 Detect the synchronization signal S _y at _-2 (step
103 and YES in step 104), timer setting section 16
_-8 and 26 _-8 is the timer value for timers 14 and 24.
_T1 is set at time _t2 (step 105).

At time _t3 , when time τ has elapsed from time _t2 , the timer 14 of the data input terminal ₁₀₁ times up (YES in step 106), and the transmission/reception control unit 1
_6-9 acquires the transmission right, but since there is no data to be sent (NO at step 107), the timer setting section _16-8 sets the timer value _T2 in the timer 14 (step 108).

At time _t4 , when time 2τ has elapsed since time _t2 , the timer 14 of the data input terminal ₁₀₂ times up (YES in step 106), and the transmission/reception control unit 1
6 _-9 acquires the transmission right. Since there is data to be sent (YES in step 107), the transmission/reception control unit 1
Step 6 _-9 activates the calling signal sending section 16 _-3 to send out the calling signal E _o to the serial data bus 30 via the P/S converting section 11 _-1 (step 112).
Here, the call signal E _o includes a call field including inquiry information ENQ, a destination terminal signal (destination address) DA to which data should be sent, an address field including the own terminal number (source address) SA that is the sender, and a call field including inquiry information ENQ. Data length field containing length information of data to be processed and check code
Consists of check fields including BCC. In this example, the data input terminal 10 ₂ sends "3" as the destination address DA and "2" as the source address SA. These addresses are sent to the calling signal sending unit 16 _-3 from the input device 13 and the terminal number holding unit 16 _-1 by the transmission/reception control unit 16 _-9 before the calling signal sending unit 16 _-3 is activated.
and is temporarily stored.

This sent out paging signal _Eo is detected by the paging signal detection sections _16-6 and _26-6 via the S/P conversion sections _11-2 and _21-2 in each data terminal (step 112, 113 YES and step 114 YES). The calling signal detection units 16 _-6 and 26 _-6 first detect the inquiry information in the calling signal _Eo .
When ENQ is detected, the call signal detection signal is extracted, followed by the destination address DA included in the address field, the sender address SA, and the data length information included in the data length field, and the transmission and reception of these information is controlled sequentially. Output to sections _16-9 and _26-9 .

In data terminals other than data terminal _10-2 that sent the calling signal _Eo , transmission/reception control units _16-9 and 2
_6-9 compares the received destination address DA with the own terminal number N held in the terminal number holding units _16-1 and _26-1 (step 115).

In this example, it is assumed that the destination address DA is "3", so in the data output terminal ₂₀₀ whose own terminal number N is "3", the transmission/reception control unit 26
_-9 activates the response signal sending unit 26 _-4 and sends a response signal.
A _c is sent to the serial data bus 30 via the P/S converter 21 _-1 (step 116). Here, the response signal A _c includes a response field containing acknowledgment information ACK, an address field containing the destination address DA to which the data should be sent and the source address SA that is the source of the data, and a check code BCC.
Consists of check fields including: in this case,
The data output terminal ₂₀₀ has “2” as the destination address DA and “3” as the source address SA.
Send out.

On the other hand, in the data terminals 10 ₀ , 10 ₁ and 20 ₁ whose own terminal number N is not "3", the transmission/reception control unit 1
6 _-9 and 26 _-9 are the timer setting section 1 for the mismatch signal.
6 _-8 and 26 _-8 and signal monitoring section 16 _-10 and 26 _-10
Output to. The timer setting units 16 _-8 and 26 _-8 that received this mismatch signal are connected to the terminal signal holding unit 16
_-1 and 26 A predetermined timer value _T3 corresponding to the own terminal number N held in _-1 is set in the timers 14 and 24 at time _t5 (step 117). Here, the timer value _T3 is expressed by the following equation.

T ₃ = (W + N) × τ ... (4) Also, the signal monitoring units 16 _-10 and 26 _-10 are activated by the above-mentioned mismatch signal, and the serial data bus 3
Monitor whether there is a signal on 0 (step
118), if there is a signal, outputs the signal present signal to the timer setting sections 16 _-8 and 26 _-8 . The timer setting sections _16-8 and _26-8 set the timer value _T3 in the timers 14 and 24 each time they receive this signal present signal (step 117). Therefore, once the timer value _T3 is set in the timers 14 and 24,
As long as the signal monitors _16-10 and _26-10 detect the signal on the serial data bus 30 before the timers 14 and 24 time out, steps 117→119
→120→118→117 loop or step 119→
It will continue to operate on a loop of 120 → 118 → 119.

The transmitted response signal A _c is detected in the data input terminal 10 ₂ by the response signal detection unit 16 _{- 7} via the S/P conversion unit 11 _{- 2} (step 1).
121 YES). The response signal detection section _16-7 detects the response signal
Detects the acknowledgment information ACK in A _c and outputs an acknowledgment signal detection signal, followed by the destination address DA and source address SA included in the address field.
and sends this information to the transmission/reception control unit 16 _-9
Output to. The transmission/reception control section _16-9 compares the received destination address DA with its own terminal signal N held in the terminal signal holding section _16-1 , and confirms that the response is for its own terminal. By setting the read/write control signal R/ to read (high level) and sequentially transmitting addresses from the address line AD, the transmit data stored in the transmit data storage area 15 _-1 is changed to the data to be transmitted. Continue sending until it runs out (NO in steps 122 and 123).

On the other hand, in the data output terminal ₂₀₀ which sent out the response signal A _c , the transmission/reception control unit _26-9 writes the read/write control signal R/ (low level) and sequentially sends out addresses from the address line AD. , the transmission data sent from the data input terminal ₁₀₂ is stored in the reception data storage area _15-2 as reception data (NO in steps 124 and 125).

In this way, the data input terminal 10 ₂ is in the transmitting state, the data input terminals 10 ₀ , 10 ₁ and the data output terminal 20 ₁ are in the synchronization signal waiting state, and the data output terminal 20 ₀ is in the receiving state.

Now, in the data output terminal ₂₀₀ that is receiving data, the transmission/reception control unit _26-9 counts how much data has been received, and this count value matches the data length information (step 1).
125 (YES) and the transmission/reception control unit 26 _-9 is set at time t ₆
Activates the response signal sending unit _26-4 and sends the response signal A _c
is sent to the serial data bus 30 (step 126).

This sent response signal A _c is detected by the response signal detection unit 26 _-7 in the data input terminal 10 ₂ in the same manner as described above (step 127).
YES), the transmission/reception control unit _16-9 activates the synchronization signal transmission unit _16-2 at time _t7 to transmit the synchronization signal _Sy to the serial data bus 30 (step 103).

This sent synchronization signal _Sy is detected by the synchronization signal detection units _16-5 and _26-6 in each data terminal (step 103, YES in step 120, and YES in step 128). As mentioned above, the synchronization signal detection sections _16-5 and _26-5 output the synchronization signal detection signal, but this synchronization signal detection signal is also output to the signal monitoring sections _16-10 and _26-10 . Data input terminals 10 ₀ , 10 ₁ that received signals
and signal monitoring unit _16-10 of data output terminal ₂₀₁
and 26 _-10 stops the signal monitoring operation.

The following operation is similar to that described above, and this time, the data input terminal 10 ₁ acquires the transmission right at time t ₈ and sends out the calling signal E _o .

In Figure 6, the data terminal is shown in steps of Figure 4.
An example of acquiring transmission rights and transmitting data using 107 was shown. On the other hand, FIG. 7 shows an example in which the data terminal acquires the transmission right in step 110 of FIG. 4 and sends data. However, since the operation in FIG. 7 can be inferred from the above explanation, the explanation will be omitted.

By the way, a certain data terminal malfunctioned, etc.
There may be cases where data transmission or reception is stopped midway. In this case, the synchronization signal
S _y is not sent even though the data terminal sending the data is supposed to send it. If this continues, the entire system will become inoperable from then on. Taking such a case into consideration, in this embodiment, one of the data terminals waiting for a synchronization signal acquires the transmission right and is able to send out the synchronization signal S _y or the paging signal E _o . There is. This will be explained below with reference to the time chart of FIG.

When the system is powered on at time t ₀ , timer value T ₀ is set in the timers 14 and 24 of each data terminal (step 101), and the data input terminal 10
₀ , the timer 14 times up at time t ₁ when time τ has elapsed from time t ₀ (YES in step 102);
A synchronizing signal _Sy is sent out (step 103).

In each data terminal, the synchronization signal detection units _16-5 and _26-5 detect this synchronization signal _Sy (step 103).
and YES in step 104), the timer setting units _16-8 and _26-8 set the timer value _T1 to the timers 14 and 24 at time _t2 (step 105).

In the data input terminal ₁₀₁ , the timer 14 times up at time _t3 , which is a time τ elapsed from time _t2 (YES in step 106), so the data input terminal 101 acquires the transmission right and there is data to be sent (step 107).
YES), so a calling signal E _o is sent (step 112).

Here, if the destination address DA included in the address field in the calling signal _Eo is "4", the data output terminal ₂₀₁ detects the calling signal _Eo (YES in step 113) and Since it is addressed to the terminal (YES in step 115), the time
A response signal A _c is sent at t ₄ (step 116).

On the other hand, the data terminals 10 ₀ , 10 ₂ and 20 ₀ are
Detects the call signal _Eo (YES in step 113),
Since the address is not addressed to the own terminal (NO in step 115), the timer setting units _16-8 and _26-8 set the timer value _T3 in the timers 14 and 24 (step 115).
117).

When the data input terminal 10 ₁ detects the response signal A _c (YES in step 121), it sends out data at time t ₅ (step 122), and the data output terminal 20
₁ receives this data (step 124).

Therefore, the data input terminal ₁₀₁ is in the transmitting state,
Data terminals 10 ₀ , 10 ₂ and 20 ₀ are in a synchronization signal waiting state, and data output terminal 20 ₁ is in a receiving state.

Now, while the data input terminal 10 ₁ in the transmitting state is sending out data, the data terminals 10 ₀ , 10 ₂ and 20 ₀ in the synchronization signal waiting state are transmitting signals from their signal monitoring units 16 _-10 and 26 _-10 . The timer setting section 1
_6-8 and _26-8 , timers 14 and 24 continue to be set to the timer value _T3 , and do not time up.

However, the data input terminal 10 ₁ shows the time
Either it breaks down at t ₆ and stops sending data midway, or
Alternatively, the data input terminal 10 ₁ has finished sending data at time t ₆ , but the data output terminal 20 ₁
Suppose that the response signal _Ac is not able to be sent out due to a failure. Therefore, from then on, in the data terminals 10 ₀ , 10 ₂ and 20 ₀ that are waiting for a synchronization signal, their signal monitoring units 16 _-10 and 26 _-10 send the signal present signal to the timer setting units 16 _-8 and 26 _-8. No output.

Therefore, in the data input terminal ₁₀₀ , the timer 14 times up at time _t7 , which is 5τ after time _t6 (YES in step 119), and outputs a time-up signal to the transmission/reception control unit _16-9 . When the transmission/reception control section _16-9 receives this time-up signal, it acquires the transmission right. Transmission/reception control section 16 _-9
has no data to send (step 129)
(NO), the synchronizing signal sending unit _16-2 is activated to send out the synchronizing signal _Sy (step 103).

Note that in the above embodiment, only the case where the response information included in the response field in the response signal A _c that is sent back from the data terminal that received the paging signal to the data terminal that sent the paging signal is the acknowledgment information ACK. However, it goes without saying that negative response information may be NAK.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, multi-drop connected
In a LAN system, all terminals share output devices such as printers and displays, so
This has the effect of making each terminal smaller. Also,
Since there is no need for a master controller, the overall system configuration is also simplified. Furthermore, since data can be exchanged directly between each terminal without any intervention, there is also the effect that it can be done in a short time.

[Brief explanation of drawings]

FIG. 1 is a system configuration diagram showing the configuration of an embodiment of a LAN system according to the present invention, and FIG.
FIG. 3 is a block diagram showing a specific example of the configuration of the data input terminal shown in FIG. 1, FIG. 4 is a block diagram showing a specific example of the configuration of the data output terminal shown in FIG. Flowcharts for explaining the operation of the data terminal shown in FIG. 1, FIGS. 5 and 6.
7 and 8 are time charts for explaining the operation of this embodiment, and FIG. 9 is a conventional LAN.
FIG. 1 is a system configuration diagram showing a system configuration. 10 ₀ to 10 ₂ ...Data input terminal, 11...
Bus transceiver, 11 _-1 ...P/S converter, 1
_1-2 ...S/P converter, 12...setting switch,
13...Input device, 14...Timer, 15...Memory, _15-1 ...Transmission data storage area, _15-2
... Received data storage area, 16 ... Control device,
16 _-1 ... Terminal number holding section, 16 _-2 ... Synchronization signal sending section, 16 _-3 ... Calling signal sending section, 16 _-4
...Response signal sending section, 16 _-5 ... Synchronization signal detection section, 16 _-6 ... Calling signal detection section, 16 _-7 ...
Response signal detection section, 16 _-8 ...Timer setting section, 16
_-9 ...Transmission/reception control section, 16 _-10 ...Signal monitoring section,
20 ₀ , 20 ₁ ...Data output terminal, 21 ... Bus transceiver, 21 _-1 ...P/S converter, 21
_-2 ...S/P converter, 22...Setting switch, 2
3... Output device, 24... Timer, 25... Memory, 25 _-1 ... Transmission data storage area, 25 _-2 ...
... Received data storage area, 26 ... Control device, 2
6 _-1 ... terminal number holding section, 26 _-2 ... synchronization signal sending section, 26 _-3 ... calling signal sending section, 26 _-4 ...
...Response signal sending unit, 26 _-5 ...Synchronization signal detection unit,
26 _-6 ... Call signal detection section, 26 _-7 ... Response signal detection section, 26 _-8 ... Timer setting section, 26 _-9 ...
...Transmission and reception control section, 26 _-10 ...Signal monitoring section, 30
...Serial data bus.

Claims (1)

[Claims] 1. In a so-called LAN system in which a plurality of terminals are multi-drop connected to one transmission path, each of the plurality of terminals has either an input device or an output device, and Terminals are assigned different terminal numbers, and each time each terminal receives a synchronization signal, it calculates the source address, own terminal number, and total number of terminals connected to the transmission path included in the synchronization signal. A predetermined timer value is set in the timer of the own terminal from Data is transmitted at a predetermined period, starting from the next smallest terminal, c. Each terminal acquires the right to transmit when its own timer times up, and d. When data is on the transmission path, all the terminals The terminal that has acquired the transmission right sets a timer value determined from the total number of terminals and its own terminal number in its own terminal's timer; or transmits the synchronization signal including its own terminal number as the source address onto the transmission path, and when the terminal with the input terminal acquires the transmission right, it transmits the data to be transmitted. If there is a LAN system, the data is directly transmitted to a terminal having the output device.