JPH0690240A - Multiplex transmission system - Google Patents

Abstract

PURPOSE:To shorten a transmission period and to accelerate response time without limiting the total number of slave stations by setting the polling to another slave station with long polling period in a standby state when the polling is applied to a slave station with short polling period. CONSTITUTION:A microprocessor MPU 2 performs polling processing according to a stored program on a ROM 3. Also, the numbers of all the slave stations 8-13 connected to a master station 1 and the values of priority are written on the ROM 3. The program is comprised of tasks equivalent to the number of priority in accordance with the priority of the slave stations 8-13, and each task is started up by the polling period decided by the priority. The master station 1 applies the polling to the slave station in accordance with the polling period sequentially at every polling period set on a priority table. When the polling is applied to the slave station with short polling period, the polling to the slave station with long polling period is set in the standby state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cyclic polling multiplex transmission system suitable for use in a local area network in the same building or in the same premises.

[0002]

2. Description of the Related Art Conventionally, a LAN (Local Area Network) has been known as a network mainly for computer communication which is built in the same building or in the same premises. LA
In N, there are several types depending on the transmission medium used, the access control method, and the like. Transmission media include twisted pair cables (twisted pair cables), coaxial cables, optical fiber cables, radios, and the like, which are used properly according to the transmission speed, distance, and the like.

In the LAN, a plurality of terminals are connected to one transmission medium, and an arbitrary terminal transfers information to another arbitrary terminal at an arbitrary timing. In the LAN, it is usual that the terminal accesses the transmission medium at its own discretion without installing a switching device so that even a small scale can be economically constructed. At this time, as a control method for enabling access without confusion, there is a polling method in which a master station inquires of each slave station whether or not it has transmission information. The polling method is characterized in that all slave stations can receive equal access.

[0004]

By the way, in the above-mentioned conventional multiplex transmission system, the terminal often handles various kinds of data, and among them, there are data which must be transmitted in a short cycle and a relatively long cycle. There is good data even in the transmission of. However, in the conventional transmission device, since the polling cycle is uniquely determined by the number of slave stations, it is not possible to handle data that needs to be transmitted at a cycle that is shorter than the polling cycle. Moreover, in order to perform data transmission in a short cycle, the number of slave stations must be significantly limited.

The present invention has been made in view of the above-mentioned circumstances, in which a priority order is set for a slave station, and the priority order of the slave station that handles data requiring a short transmission cycle is set to be high and the priority polling is performed. It is therefore an object of the present invention to provide a multiplex transmission system that can realize a short transmission cycle and improve response time without limiting the total number of slave stations.

[0006]

In order to solve the above-mentioned problems, according to the present invention, a master station and a plurality of slave stations are connected by a multiplex transmission line, and the master station sequentially connects the plurality of slave stations. In the multiplex transmission system for polling, the master station has a priority table in which a polling cycle assigned to each of the plurality of slave stations is set, and the polling cycle set in the priority table, Control means for sequentially polling slave stations corresponding to the polling cycle among the plurality of slave stations, and when slave stations with a short polling cycle are polled, polling for slave stations with a long polling cycle is performed. It is characterized by being in a standby state.

[0007]

The master station sequentially polls the slave stations corresponding to the polling cycle by the control means at each polling cycle set in the priority table. At this time, when a slave station having a short polling cycle is being polled, polling for a slave station having a long polling cycle is in a standby state.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, reference numeral 1 is a master station, which comprises a macro processor MPU 2, a read-only memory ROM 3, a readable / writable memory RAM 4, an inter-host interface circuit 5, and a slave station transmission control circuit 6. Microprocessor MPU2 is read-only memory ROM3
The polling process is performed according to the program stored in. Further, in the read-only memory ROM 3, the slave station numbers of all slave stations (described later) connected to the master station 1 and their priority (polling cycle) values are written. The program is composed of tasks prepared according to the priority order of each slave station, and each task is activated in a polling cycle determined by the priority order.

Further, the RAM 4 stores the data read from the slave station by the polling process by the microprocessor MPU2. The host-to-host interface circuit 5 exchanges transmission data with the master station (host computer) 1, commands for controlling slave stations (multiplex transmission device), and the like (not shown) such as RS-232C or GPI.
A general-purpose interface such as B, or a bus interface IC and a connector that can be connected to a specific computer bus. In addition, the slave station transmission control circuit 6
Has a function of amplifying and transmitting the polling signal to the transmission path 7 so that it can be transmitted over a long distance, and a reception function of converting the level of the signal of the transmission path 7 so that the microprocessor MPU2 can read it.

A plurality of slave stations are connected to the transmission line 7. In this embodiment, the slave stations 8 to 13 are shown.
Each slave station 8 to 13 has a specific address (hereinafter, slave station number) for deciding which slave station is to exchange data when the master station 1 exchanges data with a plurality of slave stations. Is called) is set. In this embodiment, for simplification of description, reference numerals are used. The above-mentioned polling signal is composed of an address section showing an address unique to the slave station, a data section of the transfer data, and a clearance section showing the beginning (or the end) of the polling signal. The master station 1 transmits the address part to the transmission path 7. The data section is transmitted to the transmission path 7 by the master station 1 or the slave station depending on whether it is an input or an output.

Next, a specific operation example will be described.
2 and 3 are diagrams for explaining the first embodiment, and FIG. 2 is a diagram showing the priority order of the slave stations, the polling cycle, and the number of slave stations. 3 is a time chart showing the polling process. First, as shown in FIG. 2, in this operation example, two types of priority "high" and "low" are prepared, and the polling cycle T1 of the priority "high" is "4 cycles".
And the polling cycle T2 of the priority "low" is set to "8 cycles". Further, the number of the slave stations having the priority “high” is set to “2”, and the slave station numbers are respectively assigned. Further, the number of slave stations having the priority "low" is set to "4", and the slave station numbers, ... Are respectively assigned.

Whether or not the combination of the polling cycle and the number of slave stations can be realized is determined by the following equation.

[Equation 1] Here, i is a priority order, and takes values of 1, 2, ..., N, and the smaller the numerical value, the higher the priority order. Further, ni is the number of slave stations having the priority "i", and Ti is the polling cycle required for the slave stations having the priority "i". It is feasible if the polling cycle and the number of slave stations described above are substituted into the above formula 1 and the result becomes "1".

In the master station 1, first, at time t0 shown in FIG. 3, the macro processor MPU2 executes the priority "high", that is, the task TK1 corresponding to the polling cycle T1. At this time, the task TK2 corresponding to the polling cycle T2 having the priority "low" is in the standby state. As a result of the task TK1 being executed, the first cycle C1
In the second cycle C2, the polling process is performed on the slave station number. When the task TK1 with the priority "high" is completed, the task TK2 corresponding to the priority "low" which has been in the waiting state until now is executed, and the slave station number is assigned in the third cycle C3 and the fourth cycle C4. Polling processing is performed on the other hand. When the slave station number polling process is completed, the task TK1 is executed again at time t1. Since the priority of the task TK1 is higher than that of the task TK2, the task TK2 enters the standby state, and again in the fifth and sixth cycles C5 and C6, the slave station number,
Is polled. The task TK
When 1 ends, the task TK2 in the waiting state is released from the waiting state, and the polling process is continuously performed for the slave station number in the seventh and eighth cycles C7 and C8. Hereinafter, similarly, the task TK1 and the task TK2 are executed at the set polling cycle. As a result, the slave station numbers are polled in the polling cycle T1 and the slave station numbers are polled in the polling cycle T2.

Next, FIGS. 4 and 5 are diagrams for explaining the second embodiment, and FIG. 4 is a diagram showing the priority order of the slave stations, the polling cycle, and the number of slave stations. Further, FIG. 5 is a time chart showing the polling process. First, as shown in FIG. 4, in this operation example, the priority is set to “high” and “medium”.
And three types of "low" are prepared, the polling cycle T3 of the priority "high" is set to "4", the polling cycle T4 of the priority "medium" is set to "6", and the polling cycle T5 of the priority "low" is set. Is set to "8". Further, the number of slave stations having the priority “high” is set to “1” and the slave station number is assigned. Next, the number of slave stations having the priority of "medium" is set to "2", and the slave station numbers are respectively assigned. Further, the number of slave stations having the priority “low” is set to “3”, and the slave station numbers are respectively assigned. By substituting the polling period and the number of slave stations into the above mathematical formula 1, the result is “0.958”, which is feasible.

In the master station, first, at time t0 shown in FIG. 5, the macro processor MPU2 executes the priority "high", that is, the task TK3 corresponding to the polling cycle T3. At this time, the task TK4 corresponding to the polling cycle T4 having the priority "medium" and the task TK corresponding to the polling cycle T5 having the priority "low"
5 is in a standby state. As a result of execution of task TK3,
In the first cycle C10, the polling process is performed on the slave station number. When the task TK3 having the priority “high” is completed, the task TK4 corresponding to the priority “medium” which has been in the waiting state until now is executed. Second and third cycle C1
In 1 and C12, the polling process is sequentially performed on the slave station number.

When the task TK4 ends, next, in the fourth cycle C13, the task TK5 corresponding to the priority "low" which has been in the standby state until now is executed. As a result, in the fourth cycle C13, the polling process is performed on the slave station number. Since the next cycle is the fifth cycle, the task TK3 corresponding to the priority “high” is executed again. Therefore, the task TK5 corresponding to the priority "low" is in the standby state. When the task TK3 is executed, in the fifth cycle C14, polling processing is performed on the slave station number.

When the task TK3 is completed, the task TK5 which has been in the waiting state until now is executed, and the slave station number is polled in the sixth cycle C15. In the next seventh cycle C16, since neither the task of the priority “high” nor the task of “medium” is executed,
Subsequently, the task TK5 is executed, and the polling process is performed on the slave station number. Since the next eighth cycle C17 corresponds to the sixth cycle from the execution of the slave station number described above, the task TK4 having the priority “medium” is executed, so that the slave station number is polled. Further, since the ninth cycle C18 corresponds to the fourth cycle from the execution of the previous slave station number, the task TK3 having the priority "high" is executed and the slave station number is polled. At this time, the task TK4 having the priority “medium” has a lower priority than the task TK3, and thus is in the standby state. Therefore,
The tenth task TK3 having the priority “high” is completed, and the next tenth task is executed.
In cycle C19, the task TK4 in the waiting state is executed, and the polling process for the slave station number is performed.

Thereafter, in the same manner, the slave station numbers are polled in the order of priority. As a result, the slave station having the priority "high", that is, the slave station 8 having the slave station number is polled every polling cycle T3 (= 4). Further, the slave stations having the priority "middle", that is, the slave stations 9 and 10 having the slave station number, are polled at every polling cycle T4 (= 6), and the slave stations having the priority "low", that is, the slave station number,
, Slave stations 11, 12, and 13 have a polling cycle T5.
Polled every (= 8). In the second embodiment, strictly speaking, the polling cycle T5 is 7 ≦ T5 ≦ 9.
Has become. Taking the average of these, the polling period T
In the case of 5, T5 <8, which should sufficiently satisfy the polling period shown in FIG.

[0019]

As described above, according to the present invention, a master station and a plurality of slave stations are connected by a multiplex transmission path, and the master station sequentially polls the plurality of slave stations. In the master station, the master station sets a priority table in which a polling cycle assigned to each of the plurality of slave stations is set, and the plurality of slave stations for each polling cycle set in the priority table. Out of
Control means for sequentially polling the slave stations corresponding to the polling cycle, and when the slave station with a short polling cycle is polled, the polling for the slave station with a long polling cycle is in a standby state. There is an advantage that a short transmission cycle can be realized and the response time can be improved without limiting the total number of slave stations.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a priority of slave stations, a polling cycle, and the number of slave stations in the first embodiment.

FIG. 3 is a time chart showing polling processing in the priority order shown in FIG.

FIG. 4 is a diagram showing a priority of slave stations, a polling cycle, and the number of slave stations in the second embodiment.

5 is a time chart showing a polling process in the priority order shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 master station 2 microprocessor MPU (control means) 3 read-only memory ROM (priority table) 7 transmission path (multiplex transmission path) 8-13 slave station (several slave stations) T1 to T5 polling cycle

Claims (1)

[Claims] 1. A multiplex transmission system in which a master station and a plurality of slave stations are connected by a multiplex transmission path, and the master station sequentially polls the plurality of slave stations, wherein the master station is one of the plurality of slave stations. A priority table in which a polling cycle assigned to each is set, and for each polling cycle set in the priority table, a slave station corresponding to the polling cycle among the plurality of slave stations is sequentially arranged. A multiplex transmission system comprising: polling control means, wherein when a slave station having a short polling cycle is polled, polling for a slave station having a long polling cycle is in a standby state.