JPS62171344A - Occupation prevention system for modem circuit - Google Patents

Abstract

PURPOSE:To prevent a line from being occupied owing to trouble, etc., by providing a monitoring function for a request-to-send signal (RS) and a carrier to plural terminal devices connected on a multidrop basis. CONSTITUTION:The modem 2 of a terminal device is provided newly with a carrier transmission inhibiting means 4, a carrier detecting circuit 5, and a time detecting circuit 6. The means 6 is started with the RS (request to send) and when no SD (send data) is detected within a specific time, the means 4 is operated to stop the transmission of the carrier. The means 6 is started after the transmission of SD and when the RS is still sent even after a specific time is elapsed, the means 4 stops the transmission of the carrier. The means 6 is started even when the means 5 detects the carrier and even when the stop of the carrier is not detected even after the specific time, the transmission of the carrier is stopped by the means 4. Further, even when a switch 8 is placed on its right side to set a test state continuously, the means 4 and 6 operate to stop the transmission of the carrier.

Description

[Detailed Description of the Invention] [I Already Required] One terminal among multiple terminal devices connected to a multidrop line keeps the transmission request signal (RS) of the modem interface turned ON due to a failure etc. If the carrier continues to be transmitted from the modem, the line will be occupied and other terminals will not be able to use the line. Therefore, the modem is equipped with an R3 and carrier monitoring function. When it is detected that R5 or the carrier is continuously transmitted, the transmission of the carrier is forcibly stopped to prevent the line from being occupied by a failure or the like.

[Industrial application field]

The present invention relates to a method for preventing a modem line from being occupied due to the occurrence of a failure in a terminal device connected to a multidrop line.

[Conventional technology]

A multi-drop method in which a plurality of terminal devices are connected to a host computer via a communication line is often used when the amount of data is small or when the distance between the host computer and the terminal device is long distance.

In this multi-drop system, carriers are not sent out continuously over a long period of time from a particular terminal among multiple terminals connected to the line.
Normally, it is 0N10FF in units of several seconds. Therefore, when the carrier is on for more than 10 seconds, it means that a failure has occurred in the terminal or modem.

The reasons for this situation are: ∎ If no transmission data (hereinafter referred to as SD) indicating that it is OK to transmit from the communication control device or transmission control device after sending out the carrier, ∎ SD7'1 (OFF There are four possible cases: (1) If the carrier does not stop even after the modem is in the TEST state, (2) The carrier simply stops transmitting, and (2) The modem remains in the TEST state.

[Problem that the invention seeks to solve]

In either case, a transmission request (hereinafter referred to as R3) signal that puts the modem in a transmitting state and requests carrier transmission is turned on and all terminals stop.

The object of the present invention is to provide means for quickly detecting when R3 is turned on continuously.

[Means for solving problems]

The present invention will be explained in detail with reference to the main block diagram of FIG. In the figure, carrier sending prohibition means 4. Carrier detection circuit 5. and time detection circuit 6 are newly provided in the present invention.

When the terminal 1 communicates with the host computer, the terminal 1 first sends R3 to the modem 2 and the time detection means 6. When R3 is sent out, the modem 2 starts sending out the carrier from the carrier sending circuit 3, and sends back a clear-to-send (hereinafter referred to as CS) signal to the terminal via the delay circuit 7 after a predetermined period of time has elapsed. When the terminal 1 receives the CS, it sends out the SD. The carrier sending circuit 3 puts the SD on a carrier and outputs it to the transmission line 9.

After the SD is output for a predetermined period of time, it is turned OFF, thereby stopping the carrier transmission, and then R3 and CS are also turned OFF.
Becomes FF.

The operation of the present invention when the above-mentioned situations ① to ① occur during the above series of procedures will be explained in order.

■The time detection means 6 is activated by R3 and stops when SD is output within a predetermined time, but if SD is not detected within a predetermined time, the carrier delivery prohibition means 4 is activated to prevent carrier delivery. make it stop.

■The time detection means 6 is activated when SD transmission ends, and stops when R3 stops within a certain period of time, but if R3 is still being sent out even after a predetermined period of time, the carrier sending prohibition means 4 to stop the carrier delivery. The failures in (1) and (2) are mainly due to failures in the terminal device 1.

■The time detection means 6 is also activated when the carrier detection means 5 detects the delivery of the carrier, and stops when it detects the stoppage of delivery of the front and rear wheels, but it still cannot detect the stoppage of the carrier even after a predetermined period of time has elapsed. Then, the carrier sending-out inhibiting means 4 is activated to stop sending out the carrier.

■In the event that the above carrier remains untransmitted,
In addition to a modem failure, this problem also occurs when the switch (SW) 8 in the figure is left in the test state by tilting it to the right side in the figure. In this case as well, the carrier detecting means 4 and the time detecting means 6 operate to stop the delivery of the carrier, similar to the above-mentioned case (2).

[For production]

As described above (in the present invention, the elapsed time for each step is detected by the time detection means, and if the elapsed time is longer than a predetermined value, it is determined as an abnormality and the transmission of the carrier is forcibly stopped, thereby disconnecting the line. Since the line is opened to other terminals connected to the same line, it is possible to prevent the line from being occupied due to failure of the modem or terminal.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of main parts showing the configuration of the above embodiment,
In FIG. 1, the gate circuit 4 is used as the carrier sending prohibition means 4, the loop detection circuit 5 is used as the carrier detection means 5, and the time detection means 6 is replaced with 3 second timers 21, 7.
Second timer 22. AND gate 23. This is an example configured using an inverting circuit 24 and an inverting circuit 24.

First, when R3 is sent from terminal 1 to modem 2, since SD has not yet been output, the two inputs of AND gate 23 are both "1". is output, and the 3-second timer 21 starts counting.If SD is output within 3 seconds, the output of the AND gate 21 is inverted, the counting of the 3-second timer 21 is stopped, and the terminal 1 and the host computer (Fig. (not shown)
Communication will continue as usual.

However, if the SD is still not sent after 3 seconds, 3
A signal is output from the second timer 21 to the gate circuit 4, and the gate circuit 4 is activated to cut off the carrier sending circuit, thereby stopping the carrier sending out.

Further, even if R3 does not stop after SD stops, the 3-second timer 21 similarly operates to stop sending out the carrier. That is, when the SD stops, the output of the AND gate 23 becomes "1", starts the 3-second timer 21, and within 3 seconds, the output of the AND gate 23 becomes "1".
3 does not stop, the gate circuit 4 is activated to stop the delivery of carriers.

If the carrier sending time exceeds the predetermined time, the loop circuit 5, the 7 second timer 22.3 second timer 21 monitors the carrier sending time.

That is, when the above-mentioned R3 is output, the carrier sending circuit starts sending out the carrier. The loop detection circuit 5 detects this and causes the 7 second timer 22 to start counting.

If carrier transmission stops within 7 seconds, the loop detection circuit 5
The output of the 7-second timer 22 is reversed and the 7-second timer 22 is also stopped, but if the carrier delivery does not stop after 7 seconds, the 7-second timer 22 starts the 3-second timer 21, and after another 3 seconds, the gate circuit 4 to stop the carrier delivery.

Further, when testing the modem 2, line, etc., SW8 is closed to enter the TEST state, but sometimes the user forgets to open SW8 even after the test is completed. In this case as well, the above-described loop detection circuit 5 and time detection means 6 detect the carrier sending duration time and prevent the carrier from being sent out for a predetermined period of time.

The function selection sections 25 and 26 are for selecting whether or not to use the above-mentioned functions newly provided in the present invention, and this can be achieved by, for example, connecting or disconnecting a circuit using a switch or a short bar. can. Normally, the circuit is left in a connected state, but when carrier transmission is required over a long period of time, such as when performing the above-mentioned circuit test, it is necessary to stop the newly provided function of the present invention. In such a case, the function selection sections 25 and 2
6 to open the circuit to enable carrier delivery for a long time.

In the above embodiment, an example was explained in which the setting times of the two timers for monitoring the transmission time of R3 and the carrier were set to 3 seconds and 7 seconds, but this is an example of practical values. However, the present invention is not limited to this.

〔Effect of the invention〕

As explained above (according to the present invention), it is possible to prevent all terminals from becoming unable to communicate due to a failure of a certain terminal or modem in a multidrop line.

[Brief explanation of drawings]

FIG. 1 is a block diagram of main parts showing the configuration of the present invention, and FIG. 2 is a block diagram of main parts showing an embodiment of the invention.

Claims (1)

[Claims] In a multi-drop system in which a plurality of terminals are connected via modems to a line connected to a host computer at one end, a carrier is sent from the modem (2) to the modem (2). carrier detection means (5) for detecting that
Carrier transmission prohibition means for stopping transmission of the carrier (
4) and a time detection means (6), and the time detection means (6) causes the terminal (1) connected via the modem (2) to send out a transmission request (RS) signal. elapsed time from when sending out the sending data (SD) until starting to send out the sending data (SD), and after finishing sending out the sending data (SD) until stopping sending out the sending request (RS) signal, and the carrier detection means If it is detected in (5) that any of the elapsed time from the start of carrier transmission from the modem (2) to the stop of carrier transmission exceeds a predetermined time, A modem line occupancy prevention method, characterized in that the carrier transmission prohibition means (4) is configured to stop transmission of a carrier.