JPS61158241A - Polling/selecting substitute response system for branch circuit - Google Patents

Abstract

PURPOSE:To avoid automatically the deterioration in response by using a substitute terminal equipment to secure the response to a polling/selecting mode to a terminal equipment when a time-out state is detected. CONSTITUTION:When the power supply to a terminal equipment A is cut off, a message is sent to a host computer 1 from a substitute request message transmission part 15. A time-out state is produced to the first polling or selecting signal to the equipment A after the power supply is cut off. The time-out state is detected by a detecting part 11. Then a substitute response request given from a signal generating part 12 is sent to a terminal equipment B. Thus a substitute response signal generating part 16 of the equipment B operates. Hereafter a polling/selecting state is applied to the equipment A from the computer 1. Then a substitute response is sent back from the part 16 of the equipment B. Thus no time-out state is produced and therefore no deterioration in response is produced for both equipments B and C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polling/selecting alternative response system in a branch line.

[Conventional technology]

A branch line (multidrop line) in which multiple terminal devices are connected in parallel to one host computer via a specific line.
At the same time, in order to ensure that only the terminal device of I (I!it) sends and receives data to and from the host computer,
A polling/selecting method is used.

Figure 2 is a diagram showing an example in which a plurality of terminal devices are connected to a host computer via branch lines, where 1 is the host computer, 2 is the
is a branch line, and A, B, and C are terminal devices, respectively.

As shown in the figure, even if multiple terminal devices A to C are connected, multiple terminal devices may be connected to the host computer 1 at the same time.
However, at a certain moment, transmission and reception can only be performed between any Hllil terminal device and the host computer 1.

Therefore, the host computer 1 checks each terminal device A at regular intervals.
-C is polled to inquire whether there is any data to be sent. In response to polling addressed to the terminal device itself, the terminal devices A to C transmit a signal determined depending on whether or not there is data.

Furthermore, when data is to be sent from the host computer 1, selection is applied to the terminal device to which data is to be sent in order to check whether the terminal device is in a receiving state.

If the terminal device can receive the message, it returns an affirmative response. After receiving the positive response from the terminal device, the host computer 1 transmits the data.

Assume that the power to terminal device A is now turned off. In such a case, it is not possible to respond to polling/selecting from the host W+m+ by 1. The host computer 1 waits for a certain period of time, and if no response is received within that time, that is, it times out, the terminal bag WB, C
Apply polling/selecting to.

This timeout occurs every time polling/selection is applied to a terminal device, so other terminal devices B and C
This will have a negative impact on the response.

In order to prevent such a drop in response, when the terminal device is powered off, it requests the host meter wtJl11 to stop polling, and when the terminal device is turned on again, it requests the host meter W[1] to stop polling. Request polling to be restarted. Then, on the host computer I side, the operator performs an operation to stop or restart polling each time.

[Problem that the invention seeks to solve]

As described above, a drop in response when the power of a terminal device is turned off in a branch line is prevented, but the operation for this purpose is troublesome and cannot necessarily be said to be easy.

[Means for solving problems]

SUMMARY OF THE INVENTION An object of the present invention is to provide a system that can automatically prevent a decrease in response caused by power-off of a terminal device connected to a branch line without bothering an operator on the host computer side.

In order to achieve this purpose, in the present invention, when a host computer performs polling/selecting on one terminal device and detects a timeout, the response to the evoking/selecting for that one terminal device is
Request that another terminal device take the place of that terminal device. Thereafter, this other terminal device responds in place of the one terminal device. When the one terminal device resumes service, polling/
In response to the selection, the terminal device returns a restart response. When the host computer receives the restart response, it cancels the substitution request to the other terminal device that had requested the substitution response. Thereafter, the one terminal device makes a normal response. By doing so, the aforementioned objective is achieved.

[Effect]

The time required for an alternative response is extremely short compared to waiting for a timeout. Therefore, if a terminal device stops service, polling/
During selection, a timeout will occur only - times, but after that, other terminal devices will respond in place of the terminal device whose service has been stopped, and from then on you will have to wait until the timeout occurs. Therefore, it is possible to prevent a decrease in response. Moreover, since the start and cancellation of the alternative response is automatically performed, no operation is required on the host computer side, and the complexity of the operation can be eliminated.

〔Example〕

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

FIG. 1 is a block diagram of main parts showing the system configuration of the above embodiment, in which 1 is a host computer, 2 is a branch line, 11 is a timeout detection section, 12 is an alternative response request signal generation section, 13
14 is a response restart detection unit; 14 is an alternative response stop signal generation unit; 1
Reference numeral 5 designates an alternative request message sending section, 16 an alternative response signal generating section, 17 a response restart signal generating section, and A, B, and C terminal devices, respectively.

Assume that the power to terminal device A is now turned off. At this time, the alternative request message sending unit 15 to the terminal device sends a message requesting an alternative response to the host computer 1. This message is displayed on the display screen of the host computer 1, so that the host side can know which terminal device has stopped its service.

For the first polling or selecting signal to the terminal device A after the power is turned off, a timeout occurs as in the conventional case, and is detected by the timeout detection unit 11. By this detection signal, the alternative response request signal generating section 1
2, an alternative response request is sent to the terminal device 1 other than the terminal device A, for example, the terminal device B. In the terminal device B, upon receiving this signal, the alternative response signal generating section 16 is activated.

After this, polling/selecting is also applied to the terminal device A from the host computer 1, but since an alternative response is returned from the alternative response signal generation unit 16 of the terminal device B in response, no timeout occurs. . Therefore, the response to other terminal devices B and C does not deteriorate.

When the power to the terminal bag W is turned on and the service is restarted, a response is returned from the terminal bag W, A to the polling/selecting for the terminal bag wA. This is detected by the response restart detection unit 13 of the host computer 1,
An alternative response stop signal generator 14 issues an alternative response stop signal to the terminal device B. In the terminal device B, upon receiving the alternative response stop signal, the post-transfer alternative response signal generation unit 16 stops operating and does not respond to polling/selecting for the terminal bag WA.

As described above, in this embodiment, even if each terminal device turns off the power, a timeout occurs only once and an alternative response is automatically performed, so that the response to other terminal devices is It is possible to prevent the decrease.

Moreover, since the above series of operations does not require operator intervention, handling is extremely easy.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to turn off and turn on the power of each terminal device without reducing the response to other terminal devices, and the complexity of operating branch lines is eliminated. Ru.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the main parts showing the system configuration of an embodiment of the present invention, and FIG. 2 is a block diagram of the main parts for explaining the problems of the conventional system.

Claims (1)

[Claims] A polling/selection method in which a plurality of terminal devices are connected in parallel to a specific line to which a host computer is connected at one end, and the host computer inquires whether transmission or reception is to be performed sequentially to each of the plurality of terminal devices. In a branch line in which the terminal device that received the polling/selection returns a predetermined response, the terminal device is given the right to use the line. If there is no response to polling/selecting for one of the terminal devices within a predetermined time, from then on, polling/selecting for the one terminal device will be handled by another terminal device different from the one terminal device. When one terminal device is requested to respond on behalf of the one terminal device, the other terminal device that received the request thereafter responds on behalf of the one terminal device, and the one terminal device restarts the service, In response to polling/selecting for the one terminal device, the one terminal device sends a restart response, and upon receiving the restart response, the host computer sends an alternative request to the other terminal device that had requested the alternative response. A polling/selecting alternative response method in a branch line, characterized in that the one terminal device performs a cancellation and thereafter makes a normal response.