JPS63308437A - Line exclusive prevention method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields Prior Art (Fig. 3, Fig. 4, Fig. 5) Problems to be Solved by the Invention Means for Solving the Problems (Fig. 3, Fig. 4, Fig. 5) Figure 1) Example of operation (Figures 2 and 3) Effects of the invention [Summary] A control station (for example, a host computer) and a plurality of dependent stations (
In a system in which terminal devices (for example, terminal devices) are connected via a branch line and communication is performed sequentially between the control station and each slave station, an abnormality detection unit is provided in each slave station to detect an abnormality in the slave station, and when the slave station is communicating. To forcibly down the transmission request signal from the dependent station to the modem so that no transmission data is output on the line.

[Industrial application field]

The present invention relates to a system in which a control station (for example, a host computer) and a plurality of dependent stations (for example, terminal devices) are connected by branch lines.

When connecting a large number of terminal devices to a host computer,
Providing a dedicated line for each terminal,
Although this is a preferable form because it is simple in terms of configuration, it requires a great deal of expense to install a dedicated line for this purpose.

Therefore, it is widely practiced to connect a large number of terminal devices using one line.

[Conventional technology]

Fig. 4 is a diagram showing an overview of the entire system that connects a control station and a terminal via one line, and Fig. 5 is a diagram showing details of the connection between the terminal-side modem and the terminal in this system. be.

In FIG. 4, reference numeral 40 denotes a control station, such as a host computer, which is connected to one line 43 via a modem 41, and further connected to dependent stations (terminals) A and B via modems 42a, 42b, and -42n, respectively. , -N.

FIG. 5 shows in more detail the connection state between the modem on the terminal side and the terminal. One line 43 connecting with the control station (host computer) is composed of a transmitting line and a receiving line, and connects modems 42a, 42b- and terminal A.
, B-, as shown in the figure, a signal line for sending data SD that sends data from the terminal to the modem side, a signal line for receiving data RD that sends data from the modem side to the terminal, and a signal line for sending request signal R3. and a signal line for a transmission permission signal CS.

In such a system, as shown in FIG. 3, when a polling signal for terminal A, that is, transmission request data 30, is sent from the control station (host computer) side to the signal line for the received data signal SD, terminal A A transmission request signal (R3 signal) 32 is issued to the modem 42a. In response to this, the modem 42a turns on the transmission permission signal (C3 signal) 33.
and transmits the transmission data signal (SD double signal 31) to the host computer side.

[Problem that the invention seeks to solve]

In the above-mentioned system, if a software runaway or hardware malfunction occurs on a terminal that is using the line, and the terminal goes down, the line remains exclusive, and other terminals connected to this line are All of them have the problem that communication with the host computer becomes impossible.

That is, in FIG. 3, when a polling signal, that is, transmission request data 35 is sent from the host computer to terminal B, terminal B sends the modem 42 if there is data to be transmitted.
The modem 42b sends a transmission request signal (R8 signal) 37 to the modem 42b, and in response to this, the modem 42b returns a transmission permission signal (C3 signal) 38, and upon seeing this, transmits the transmission data signal (SD double signal 36). However, at this time, if a system failure occurs on the B terminal side, the R3 signal remains on as shown by the broken line 37' in Figure 3, and the transmitted data remains on the line.In this state, When terminal A receives data requested to be sent from the host computer, it sends the data to the host computer using the procedure described above, but since the data sent by terminals B and A are combined on the line,
The problem is that the host side cannot receive correct data.

This invention was made in view of the above points, and in a system in which multiple terminals are connected to a host computer by a branch line, even if the terminal that is using the line goes down, the line can be maintained. The purpose is to provide a line monopolization prevention method that does not output abnormal data.

[Means for solving problems]

FIG. 1 shows a diagram of the principle of this invention.

In the figure, 10 is a line control unit provided in the terminal device, which controls the transmission permission signal (C3) line, the transmission data (S D
) line and a received data (RD) line are connected to a modem (not shown). According to the present invention, an error detection circuit 11 is provided to detect an error in data from the terminal body, and a signal when an error is detected is connected to an AND circuit 14 via an inverter.

[Effect]

When the error detection unit 11 detects an error, it outputs "1", which is transmitted to the AND circuit 14 via the inverter 13, sets one input line 12 of the AND circuit 14 to "0", and sends a transmission request to the modem. Since the signal R3 is rOJ,
This allows the transmission data SD to be forcibly brought down.

〔Example〕

FIG. 2 shows an embodiment of this invention. In the figure, the same symbols as in FIG. 1 indicate the same parts.

In FIG. 2, 10 is a line control unit provided in the terminal, to which is connected a data line 17 from the terminal body, and a signal line for transmission data SD, which is a signal line to the modem. The transmission request signal R is an output signal from
A signal line for 5 and a signal line for a transmission permission signal CS are connected. 11 is an error detection unit provided according to the present invention; for example, 11-0 is a parity error check unit that checks data bus errors, and 11-1 is an unimplemented memory area access check unit that checks undefined Detects access to the area and checks address bus errors. The error detection signals from these check sections are sent to an AND circuit 14 via an OR circuit 15 and an inverter 13.
Connect to one input of the

Another input of the AND circuit 14 is connected to the line control unit 10.
A transmission request signal R3 is input from the terminal.

Therefore, this transmission request signal R3 is controlled by the output of the inverter 13 and sent to the modem.

Now, if neither the parity error check section 11-0 nor the unimplemented memory area access check sections 11-1 detects an error, their outputs are all "0", and the output of the inverter 13 is "0". 1". Therefore, in such a state, when a polling signal, that is, transmission request data is transmitted from the host computer side to the terminal, the line control unit 10 of this terminal transmits the transmission request signal R on the signal line 1st.
Outputs 8. This transmission request signal R3 is input to the AND circuit 14 through the signal line 1, but if there is no error on the terminal side, the output of the inverter 13 is "1", and this is sent to the modem via the AND circuit 14. Sent out.

In response to this R3, the modem returns a transmission permission signal C8, so that the terminal transmits the transmission data SD.

In such a state, if a failure such as a parity error occurs on the terminal side, this is detected by the parity error check unit 11.
−〇 detects this and outputs “1”. Therefore, the output of the inverter 13 becomes "0", and the output of the AND circuit 14 becomes "0".
One input becomes rOJ. Therefore, the signal on the signal line 16 becomes "0" (see the solid line portion of the R3 signal 37 in FIG. 3), and the C8 signal also becomes rOJ, so the transmission data SD is brought down.

〔Effect of the invention〕

As described above, according to the present invention, when a system failure occurs in a terminal that is using the line, transmission data is immediately stopped, so there is no collision with data from other terminals on the line, and No abnormal data is output on the line.

[Brief explanation of drawings]

Fig. 1 is a diagram illustrating the principle of this invention, Fig. 2 is a configuration diagram of an embodiment of this invention, Fig. 3 is a diagram showing the operation of this invention and the operation of a conventional example, and Fig. 4 is a diagram illustrating the operation of this invention and a conventional example. A system configuration diagram of FIG. 5 is an explanatory diagram of a conventional example. 10-Line control section 11-Error detection section 13-Inverter 14-AND circuit missing example Fig. 2

Claims (3)

[Claims] (1) In a system in which a control station and multiple dependent stations are connected via branch lines and communication is performed between the control station and each dependent station sequentially, an abnormality detection means (11) is provided in each dependent station to detect an abnormality in the dependent station. A line monopolization prevention method characterized in that, when detection is detected, the operation of outputting a transmission request signal (RS) of this dependent station is stopped. (2) The line monopolization prevention system according to claim 1, wherein the abnormality detection means is a parity error check means for checking a parity error. (3) The above abnormality detection means checks accesses to undefined areas of memory.
The line monopoly prevention method according to claim 1, characterized in that it is a checking means.