JPH01183237A - Data link establishment method - Google Patents

Abstract

PURPOSE:To recognize the presence or absence of a response in a short time by setting the timer time of a no response timer in a short time and executing polling with respect to slave stations apart from a data link. CONSTITUTION:When a main station 1 sequentially executes polling the slave stations 2, the timer time of the silence timer which decides the slave stations to be no response is set to be the timer time for a long time TL with respect to the slave station which is not decided to be no response in a preceding time, and to the timer time TS shorter than TL with respect to the slave station which is decided to be no response in the preceding time. It is usual for the normal slave station to execute a control action based on the action instruction from a manual operation or the main station, and the comparatively long time TL is used for the timer time. Since the slave station which is no response in the preceding time does not execute such a control action, the considerably short time can be set for the timer time TS if the slave station is certainly set to stand by for data communication when a system recovers from the condition of a fault or power block, and the efficiency of data transmission can be improved.

Description

[Detailed description of the invention] [Industrial application field]

The present invention is applied to a so-called polling data transmission system in which one master station sequentially designates a plurality of slave stations and communicates data with each slave station each time the master station designates a plurality of slave stations. This relates to a method for re-establishing a data link between a slave station and a master station that had been disconnected.In particular, it is possible to automatically establish a data link when a slave station that has been unable to communicate returns to a state in which communication is possible, and that this slave station can The present invention relates to a data link establishment method that allows the entire polling to be completed in a short time even when the data link is in a disabled state.

[Conventional technology]

With this type of data link establishment method, a data link could not be established. Another method is to continue polling for a slave station that cannot be established in the same way as for a normal slave station.Another method is to exclude a slave station that has not responded from the polling target and to allow that slave station to communicate. There is a known method for re-establishing a data link by manually transmitting a message to the master station using a key or the like when the state returns to a possible state, and restarting polling for the slave station. .

[Problem to be solved by the invention]

However, according to method (2) above, when the slave station returns to a communicable state, a data link is automatically established, but if it takes a long time to determine that there is no response, the communicable state remains. If the polling continues, it takes time to make the determination, and it takes a long time to finish polling all the slave stations, resulting in poor data collection efficiency. In addition, in the method (2) described above, various tasks from excluding polling to restarting polling for the slave station in question are troublesome.
There is a problem in that it is particularly inconvenient when the master station and slave station are far apart. Therefore, an object of the present invention is to set the timer time of the no-response timer until the master station determines that the slave station has become unresponsive during polling by the master station. In this case, the problem described above is solved by providing a data link establishment method that sets a shorter timer time unless the slave station returns to a state where communication is possible. The purpose is to automatically establish a data link when the device returns, and also to be able to complete the entire polling in a short time even during a period when communication is not possible.

[Means to solve the problem]

In order to achieve the above object, the method of the present invention comprises an r main station (such as 1) and a plurality of slave stations (such as 2), and the master station performs an operation of sequentially specifying the slave stations in a predetermined order. The data transmission system repeatedly performs data communication with the relevant slave station each time this designation is made, wherein after the designation by the master station, the relevant slave station communicates with the master station within a first period (such as timer time TL). In the data transmission system, when the master station does not respond to the slave station, the master station determines the slave station to be a non-responsive station, and shifts to the data communication with the slave station next to the slave station. , From the next time onwards, after the main station specifies the non-responsive station, the non-responsive station responds to the main station within a second period (timer time TS, etc.) that is shorter than the first period. Unless otherwise specified, the master station shall again determine the slave station to be a non-responsive station and proceed to the data communication with the slave station next to the slave station.

[For use]

This invention polls slave stations with which a data link has already been established by setting a necessary predetermined no-response timer time, and polls slave stations that are disconnected from the data link for a shorter time. The timer time of the response timer is set and polling is performed to confirm the presence or absence of a response within a short period of time.

【Example】

Next, the present invention will be explained in detail using FIGS. 1 and 2. FIG. 1 shows an example of a data transmission system to which the present invention is applied. Master station 1 has slave station 2 (2-1, ~,
It is assumed that the system configuration is registered to poll 2-n). Further, in the master station 1, the timer is used for a normal slave station 2 as a set timer time of a non-response timer 3 for determining whether there is a response from the slave station 2 in response to polling from the master station 1. A timer time TL with a longer time (e.g., several 100111 seconds to several 5 ec) and a timer with a shorter time (e.g., several seconds to several tens of m5) used for slave station 2 that did not respond to the previous polling for some reason. A time TS is set. FIG. 2 is a flowchart showing the main operations of the main station 1 in FIG. To explain the figure, the master station 1 first specifies the number i of the slave station 2 to be polled as 1 (step 11), and then if the slave station 2 (with the number i) did not respond last time ( Step 122 branch N), set the timer time of no-response timer 3 to TL.Step 13)
, on the other hand, if there is no response (step 121 branch Y), the timer time of the no-response timer 3 is set to a TS shorter than the TL (step 14). Then, a polling operation to the slave station 2 is performed, that is, a signal specifying the address (number i) for the slave station 2 and a command to start data transmission are transmitted (step 15). Next, before the timer time TL or TS set for the non-response timer 3 elapses, there is a response from the slave station ・2 and data transmission is performed (step 161 branch Y
), and after processing the data (step 17), the relevant slave station 2 is re-memorized as being normal. Therefore, when the relevant slave station 2 did not respond last time, the memory of the non-response is cleared (step 18). However, in step 16, if there is no response from the slave station after the timer time TL or TS has elapsed (branch N).
, the relevant slave station 2 is re-memorized as being non-responsive 6 (step 19). Then, the number i of the slave station 2 is incremented (step 20) until the number i reaches n+1, in other words, until the polling for all slave stations 2 up to number n is finished (step 213 branch N). Returning to step 12, the above series of operations is repeated for the next slave station 2 with number i. When polling for slave stations 2 up to number n is completed in this way (step 212 branch Y), it is assumed that all polling operations have been completed and the process proceeds to a procedure not shown. Each time a predetermined condition is met, the polling operation from step 11 is repeated from next time onwards.

【Effect of the invention】

According to the present invention, when the master station sequentially polls the slave stations, the timer time of the no-response timer that determines the slave stations as non-responsive is set to a long TL for the slave stations that were not previously determined to be non-responsive. , and for slave stations that were previously determined to have received no response, the TS is set to be shorter than the TL. In this way, the function of a normal slave station is not limited to data communication; it usually performs control operations based on human operations or operation commands from the master station (not shown in Figure 2). Therefore, a relatively long time is used as the timer time TL, but since the slave station that did not respond last time did not perform such control operations, it is necessary to If the device is kept on standby for data communication, it is possible to set an extremely short time as the timer time TS, and the efficiency of data transmission can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram as an embodiment of the present invention, and FIG. 2 is a flowchart for explaining the operation of the main part of FIG. 1. 1: Master station, 2 (2-1, ~, 2-n): Slave station, 3: No response timer, TL, TS: Timer time. (Notification) Main station 1 Eo 1 -

Claims (1)

[Claims] 1) A data transmission system comprising a main station and a plurality of slave stations, wherein the master station repeats an operation of sequentially designating the slave stations in a predetermined order, and each time the master station performs data communication with the corresponding slave station. In the system, if the slave station does not respond to the master station within a first period after the designation by the master station, the master station determines the slave station to be a non-responsive station. In a data transmission system in which the master station shifts to the data communication with the slave station next to the slave station, from the next time onwards, after the master station makes the above designation to the non-responsive station, does not respond to the master station within a second period shorter than the first period, the master station again determines the slave station to be a non-responsive station and ranks it next to the slave station. A method for establishing a data link, characterized in that the data communication is shifted to the above-mentioned data communication with a slave station.