A Communication Command Execution Mode of Programmable Controller

Abstract

The invention discloses a coCommunication instruction execution mode of a PLC (programmable logic controller). The coCommunication instruction execution mode comprises steps of establishing a communication instruction execution table, wherein the communication instruction execution table is provided with an instruction execution permission flag and an instruction execution completion flag; performing scanning of PLC programs via a PLC program scanning process A, when a communication instruction is scanned, searching for a corresponding communication instruction in the communication instruction execution table, according to an enable end state of the communication instruction in the program (Yes means allowing the communication instruction execution, No means not allowing the communication instruction execution), determining, in a comprehensive way, whether to modify the instruction execution permission flag based on combination of the instruction execution permission flag and the instruction execution completion flag in the communication instruction execution table, and reading an instruction execution result and an instruction error code; and scanning the communication instruction execution table in a cycling way via use of a separate communication instruction execution process B, and determining whether to execute the instruction according to the instruction execution permission flag in the communication instruction execution table. The PLC program scanning process A and the communication instruction execution process B operate asynchronously and in parallel.

Description

technical field [0001] The invention relates to the field of programmable controllers, in particular to a method for executing communication instructions of a programmable controller. Background technique [0002] Each programmable logic controller (PLC) has its own communication instructions, and they rely on communication instructions to communicate with third-party equipment. Existing PLC communication instruction execution methods mainly use the following execution methods: PLC program scanning process A to PLC program Scanning execution, when a communication command is scanned, if the communication port is free and the communication command enable terminal has power, then execute the communication command; otherwise, skip the communication command and continue to scan and execute the next command. Since the execution of the communication command is an independent and relatively long process, when executing the communication command, it needs to prepare to send the comma...

AI Technical Summary

Problems solved by technology

[0004] 1. The communication efficiency is low. If the PLC program scan cycle is 30ms, there may be a scan cycle interval between the execution of two communication instructions;

[0005] 2. The programming is complex, requiring the user to control the timing of the communication command execution in the program, and when the communication command fails to execute, it is impossible to intuitively judge whether it is caused by the program logic problem or the communication command itself;

[0006] 3. In the case of multi-slave communication (multiple communication commands), it is impossible to ensure that all communication commands have equal chances of execution. In the case of coupling between the program scan cycle and the communication command execution cycle, some communication commands have no chance to be executed.

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