JPH03237547A - Peripheral device switching system - Google Patents

Abstract

PURPOSE:To eliminate a need of a special processing means by switching a peripheral device to another designated peripheral device after sending a trans mission stop request signal to peripheral devices, which transmit data at present, at the time of a switching request designating the peripheral device. CONSTITUTION:A host computer 11 generates a required instruction to transmit and receive data to an from low order devices and a peripheral device switching device 13 is connected to this computer 11 by a transmission line 12. This device 13 has a function to connect the computer 11 and a designated device, for exam ple, a peripheral device 14 by switching at the time of the issue of a switching request designating the specific peripheral device 14 from the computer 11. If a peripheral device 15 transmits and receives data to and from the computer 11 at the time of the issue of this switching request, the device 13 sends the transmission stop request signal to the peripheral device 15, and switching to the peripheral device 14 is performed when the stop response comes there after.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Field of Application) The present invention switches and selects specific peripheral devices, such as a host computer, a host computer, etc. (hereinafter referred to as a host computer).
This paper relates to improvements in peripheral device switching methods connected to .

(Prior Art) Conventionally, data transmission systems in which multiple peripheral devices are connected to a host computer via a peripheral device switching device and data is exchanged between the host computer and a specific peripheral device have been widely used in various fields. It's being used.

By the way, in the peripheral device switching device of such a data transmission system, when there is a peripheral device switching request from the host computer, even though data is being exchanged between the peripheral device at the current location and the host computer, Peripheral devices that have received a switching request are switched and connected to the host computer.

(Problem to be Solved by the Invention) Therefore, in the data transmission system as described above, if a switching operation is performed while data is actually being sent and received between the host computer and the peripheral device, the host computer will not be able to access the data at all. To recognize the pig as a different pig, a judgment method is required to accurately recognize the data, or if it is determined that the data is unnecessary and has no meaning, it is necessary to erase the data from memory, and signal processing is required. becomes extremely complicated.

The present invention has been made in view of the above circumstances, and provides a peripheral device switching method that prevents the data from being recognized as different data by appropriately switching the timing with the transmitted and received data when a switching request is made. With the goal.

[Structure of the Invention (Means and Effects for Solving the Problems) In order to solve the above problems, the present invention provides a system in which a plurality of peripheral devices are connected to a host computer via a peripheral device switching device, and when a switching request is received, In the peripheral device switching method in which the peripheral device switching device connects a specific peripheral device and the host computer to enable data exchange operations, the peripheral device switching device specifies the peripheral device from the host computer. When a switching request is made, if there is a peripheral device currently transmitting data, a transmission stop request signal is sent to the peripheral device currently transmitting data, and a signal indicating that the peripheral device currently transmitting data has stopped transmitting data. By switching the connection to the specified peripheral device when receiving the transmission stop request signal, the peripheral device that has received the transmission stop request signal can take appropriate transmission termination measures, etc., and the data will not be recognized as incorrect data.

(Embodiment) Hereinafter, a data transmission system to which a peripheral device switching method according to the present invention is applied will be described with reference to FIG. In the figure, 11 is a host computer that generates necessary commands and exchanges data with lower-order devices;
A peripheral device switching device 13 is connected to this host computer 11 via a transmission line 12 .

This peripheral device switching device 13 has a function of switching and connecting the host computer 11 and its designated device, for example, the peripheral device 14, when there is a switching request from the host computer 11 to designate a specific peripheral device 14. There is. Moreover, when there is a switching request, this peripheral device switching device 13 switches the peripheral device 15 that is currently exchanging data with the host computer 11, if there is one.
The configuration is such that a transmission stop request signal is sent to the peripheral device 14, and the switch is made to the peripheral device 14 side only when a stop response is received thereafter.

These peripheral devices 14, 15. For example, in the case of plant instrumentation, this corresponds to, for example, a digital controller installed at various locations on a process line, and in addition to the functions of detecting and manipulating process quantities, it also has a microcomputer and data transmission means. .

Therefore, according to the configuration of the data transmission system as described above, the peripheral device switching device 13 specifies the peripheral device from the host computer 11 at predetermined intervals and requests switching, as shown in FIGS. 2 and 3. (STI). Here, when it is determined that there is a switching request, the specified data of the peripheral device is stored in the memory (Sr
1). Thereafter, the process moves to the next step ST3, where it is determined whether there is a peripheral device currently transmitting data or not, and when it is determined that there is no peripheral device currently transmitting data, it is switched to the designated peripheral device side (Sr4). In FIG. 2, 81 indicates transmission data. If it is determined in step ST3 that there is a peripheral device currently transmitting, a transmission stop request signal S is sent to the peripheral device.
2 is sent (Sr5).

After sending the transmission stop request signal S2, a timer is driven to determine whether a predetermined time has elapsed (5T6), and if the predetermined time has not elapsed, the peripheral device responds with a stop response S3. 5T7), and if there is no stop response S3, proceed to step ST.
Return to step 6 and execute the same process again, while the stop response S
3, the connection is made to the peripheral device specified by the host computer 11. Note that if there is no stop response even after a predetermined period of time has elapsed in step S6, it is determined that the peripheral device is abnormal, and this is notified to the host computer 11, and if there is an operator on the peripheral device side, is notified by means such as an alarm (Sr1).

Therefore, if another peripheral device is transmitting data when a switching request is made, a transmission stop request signal S is sent to that peripheral device.
Since the peripheral device that made the switching request will not switch to the side that made the switch request until it receives the stop response s3 after sending 2, the peripheral device that is currently transmitting will finish transmitting data in an appropriate state and respond to the stop response S3.
Not only can the destination device, that is, the higher-level computer 11, also know that the transmitted data has ended in an appropriate state, and the higher-level computer 11 can recognize it as incorrect data or send unnecessary data. It does not erase data that has already been stored.

In the above embodiment, digital controllers are assumed as the peripheral devices 14, 15°, . . . , but there is no particular limitation on the type of the devices; for example, they may be computers. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, when a switching request is made by specifying a peripheral device, if there is another peripheral device currently transmitting, a transmission stop request is sent to that peripheral device. When a stop response is received after sending a signal, the switch is made to the designated peripheral device side, so there is no need for special processing means on the host computer, and there is no need to send or receive incorrect data, so the data is always correct. It can be treated as

[Brief explanation of drawings]

1 to 3 are shown to explain an embodiment of the peripheral device switching method according to the present invention, and FIG. 1 is a configuration diagram of a data transmission system to which the method of the present invention is applied;
FIG. 2 is a diagram showing the exchange of data between the peripheral equipment switching device and the peripheral equipment, and FIG. 3 is a flowchart explaining the operation of the system of the present invention. 11... Upper computer, 12... Transmission line,
13... Peripheral device switching device, 14, 15. ···Peripheral equipment.

Claims (1)

[Scope of Claims] A plurality of peripheral devices are connected to a host computer via a peripheral device switching device, and upon receiving a switching request, the peripheral device switching device connects a specific peripheral device and the host computer to transfer data. In a peripheral device switching method that enables sending and receiving operations, the peripheral device switching device determines that, when a switching request is received from the host computer to specify a specific peripheral device, there is another peripheral device that is currently transmitting data. In this case, a transmission stop request signal is sent to the other peripheral device, and when a signal indicating that transmission has been stopped is received from the other peripheral device that is currently transmitting data, it is instructed to switch to the specified specific peripheral device. A peripheral device switching method characterized by the following.