JPH03282906A - Programmable controller for distributed control system - Google Patents

Abstract

PURPOSE:To always accurately recognize the maximum value of data link refresh cycle time by detecting the cycle time between plural programmable controllers(PCs), storing data relating to the maximum value of the cycle time, transferring the stored contents to a display means, and displaying the transferred contents. CONSTITUTION:Plural PCs are connected to a link signal line through a communication IF 35 and initialized at first. Then, whether a communication cycle has been completed or not is discriminated, and at time time of completing the cycle, whether the completion is the initial time or not is discriminated. When the discrimination is NO, a timer module 34 calculates the refresh cycle time (Rt) of a data link from a time difference between current time and the preceding communication cycle completion. Then whether the current value of the Rt is larger than the maximum value of the Rt stored in an internal RAM 32 or not is discriminated, and when the current value is larger, the maximum value data in the RAM 32 are updated. Then the current time is stored in the RAM 32 as the preceding communication cycle completion time and displayed on the screen of a CRT 54. Consequently, the maximum value of the data link Rt can be always accurately recognized without executing calculation or measurement.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a programmable controller for a distributed control system, and particularly to a type of distributed control in which control data is exchanged asynchronously between a plurality of programmable controllers. This relates to a system/7 programmable controller.

(Prior art) A programmable controller is provided for each target machine, and control data such as interlocks, feedback, and control commands between each machine are repeatedly transmitted between each programmable controller at a predetermined communication cycle using a link system. Distributed control systems are already well known.

In the above-mentioned distributed control system, the main body operation cycle and communication cycle (link cycle) of the programmable controller provided for each target machine are often asynchronous, so control data is transmitted through communication between programmable controllers. The evening refresh cycle, ie, the data link refresh cycle, changes depending on the timing of communication commands.

(Problem to be solved by the invention) The maximum cycle time of the refresh cycle of control data through communication between programmable controllers can be calculated from the main body cycle time and communication cycle time of each programmable controller, but this is only a calculation. This data may therefore differ from the actual value. In addition, the actual data link reflex cycle time changes depending on the network traffic environment, so the calculation formula differs accordingly. Taking this into consideration, the calculation formula for the maximum cycle time becomes complicated. , which is difficult for users to understand, and also requires time and effort to measure in actual user systems.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a programmable controller for a distributed control system that can display the actual data link refresh cycle time to the user based on actual measurements.

(Means for Solving the Problems) According to the present invention, the above object is to provide a programmable controller for a distributed control system in which control data is repeatedly transmitted between a plurality of programmable controllers in a predetermined communication cycle. , a timer means for detecting a data link refresh cycle time by measuring time for each communication for a data link between a plurality of programmable controllers, and a maximum data link refresh cycle time detected by the timer means. For a distributed control system, comprising a storage means for storing data regarding the value, and a control means for transferring data regarding the maximum value of the data link refresh cycle time stored in the storage means to the display means. Achieved by a programmable controller.

(Function) According to the above configuration, the data link refresh cycle time is detected by the timer means, data regarding the maximum value thereof is stored in the storage device, and the maximum value of the data link refresh cycle time stored in the storage device is detected. The data regarding the maximum value of the data link refresh cycle time is transferred by the control means to a display means such as a CRT, so that the data regarding the maximum value of the data link refresh cycle time is displayed on the screen.

(Example) The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a distributed control system of programmable controllers. In this distributed control system, a plurality of programmable controllers 10 provided for each target machine (not shown) send link signals for data links. They are connected to each other by lines 12.

FIG. 2 shows the basic configuration of the programmable controller 10, and the programmable controller 10 includes an arithmetic unit (main unit) 20 and a communication unit 30.
and an input/output crab knit 40 for the target machine.

The arithmetic unit 20 includes a CPU 21 configured by a microprocessor, an internal RAM 22, a system ROM 23 storing a system program, an input/output RAM 24 storing input/output data, and a shared RAM 25 storing transmitted/received data. There is.

The communication unit 30 includes a CPU 31, an internal RAM 32, a system program ROM 3B storing a system program for communication, a timer module 34 for measuring time, and a communication interface circuit 35.

A terminal device 50 is connected to the path line 14 of the programmable controller 10, and the terminal device 50 has a keyboard 52 and a CRT as a display means.
54.

The system program stored in the system ROM 33 of the communication unit 30 includes a data link refresh cycle time measurement program, and according to this program, the timer module 34 measures the data link refresh cycle time for each communication between the plurality of programmable controllers 10. The internal R
The AM 32 stores data regarding the maximum value of the data link refresh cycle time detected by the timer module 34, and the CPU 31 stores data regarding the maximum value of the data link refresh cycle time stored in the internal RAM 32 from the keyboard 52 of the terminal device 50. Transfer to the CRT 54 is controlled based on user commands and the like.

As a result, data regarding the maximum value of the data link refresh cycle time is displayed on the screen on the CRT 54.

Furthermore, the internal RAM 32 stores data related to the current refresh cycle time in addition to data related to the maximum value of the data link refresh cycle time, and even if this data is displayed on the CRT 54 at the same time as the data related to the maximum value. good.

FIG. 3 shows a data link refresh cycle time measurement routine in a programmable controller according to the present invention.

In this routine, first, in step 10, the generation time is cleared, and then in step 12, the refresh cycle time is cleared. This step 10
Step 12 is a so-called initialization processing step.

In step 14, it is determined whether the communication cycle is completed or not, and if the communication cycle is completed, step 16 is executed next.

In step 16, it is determined whether the communication cycle is completed for the first time. If it is the first time, jump to step 24, otherwise proceed to step 18.

In step 18, the refresh cycle time of the data link is calculated from the difference between the current time measured by the timer module 34 and the time when the previous communication cycle was completed.

After step 18, the process proceeds to step 20.

In step 20, the refresh cycle time calculated in step 18, that is, the current value is already within the internal RA.
It is determined whether the refresh cycle time is greater than the maximum value stored in M32. If the current value is greater than the maximum value so far, proceed to step 22;
If not, jump to step 24.

In step 22, data regarding the maximum refresh cycle time stored in the internal RAM 32 is updated to the current value.

In step 24, the current time, that is, the time when the current communication cycle was completed, is stored in the internal RAM 32 as the time when the previous communication cycle was completed.

FIG. 4 shows the data area for measuring the refresh cycle time of the memory map in the internal RAM 32. As is clear from FIG. 4, the internal RAM 32 includes an area for storing the current value of the refresh cycle, an area for storing the maximum value of the refresh cycle time, and an area for storing the previous time.

FIG. 5 shows an example of a data link refresh cycle that may occur when the service cycle and communication cycle of the programmable controller are asynchronous.

As is clear from FIG. 5, the refresh cycle changes from time to time due to factors such as the difference between the main body service cycle and the communication cycle, but the maximum refresh cycle time is determined by the terminal device 50 as necessary.
The user can accurately recognize the maximum value of the data link refresh cycle time specific to the distributed control system at any time as needed. It will be effectively used for setting takt time etc.

(Effects of the Invention) As is clear from the above explanation, in the programmable controller for a distributed control system according to the present invention, the data link refresh cycle time is actually measured, and this is clearly displayed to the user etc. by the display means. Therefore, the user can always accurately recognize the maximum value of the data link refresh cycle time without performing troublesome calculations or measurements.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing an example of a distributed control system for a programmable controller, FIG. 2 is a block diagram showing an example of a programmable controller for a distributed control system according to the present invention, and FIG. 3 is a distributed control system according to the present invention. 4 is a memory map diagram showing the data area of the internal RAM used for measuring the refresh cycle time, and FIG. 5 is a flowchart showing the refresh cycle time measurement routine in the programmable controller. 3 is a time chart showing an example of a refresh cycle. 10...Programmable controller 12...Link signal line 20...Arithmetic unit 30...Communication unit 40...Input/output crab unit 50...Terminal device 54...CRT

Claims (1)

[Claims] 1. In a programmable controller for a distributed control system in which control data is repeatedly transmitted between a plurality of programmable controllers in a predetermined communication cycle, a data link between the plurality of programmable controllers is provided. a timer means for detecting a data link refresh cycle time by measuring time for each communication; a storage means for storing data regarding a maximum value of the data link refresh cycle time detected by the timer means; and the storage means. A programmable controller for a distributed control system, comprising: control means for transferring data regarding the maximum value of a data link refresh cycle time stored in the display means to a display means;