Communication method for programmable logic controller and extension module

Abstract

The invention provides a communication method for a programmable logic controller and an extension module. A communication protocol state machine controller and an I / O refresh state machine controller recognize periodic I / O refresh data frames and nonperiodic state data frames, can instantly send notification to the I / O refresh state machine controller to require the I / O refresh state machine controller to respond to the received state data frames when recognizing the sent nonperiodic state data frames, and can automatically respond and perform data read-write when recognizing the sent I / O refresh data frames so as to lighten the load of the I / O refresh state machine controller and improve communication speed and efficiency; meanwhile, the communication method adopts serial communication lines for connection, has few lead wires and low cost, saves capital goods resource and achieves the aim of the invention.

Description

technical field [0001] The invention relates to a communication method of a programmable logic controller (Programmable Logical Controller, PLC), in particular to a communication method between a programmable logic controller and an expansion module. Background technique [0002] Programmable Logical Controller (PLC) is an electronic device that provides input signals and executes user programs to control output signals and mechanical actions. The number of I / O terminals of existing PLC hosts is Fixed, when more I / O terminals need to be expanded, various expansion modules need to be added to increase the number of I / O terminals. [0003] Existing programmable logic controller PLCs are generally composed of programmable logic controller PLC mainframe plus expansion modules. The connection methods of expansion modules include backplane connection and side step-by-step connection. Since the backplane connection occupies more hardware resources, large installation space and hig...

AI Technical Summary

Problems solved by technology

The method of selecting a group of address lines to transmit addresses is inflexible in hardware design. The maximum number of address lines determines the maximum number of expansion modules. Different programmable logic controller PLC host models have different numbers of address lines. The number of hard-connected cables may be different, and the cables connected to the side are not universal; and this method is essentially time-sharing transmission of addresses, commands and data. The address lines are parallel and the anti-interference ability is poor, so a group of addresses is selected. There are also major disadvantages of the line method

In addition, it is not flexible to use the method of setting the address by dialing the code. Every time the order or quantity of the expansion modules is changed, the address needs to be reset, which is inefficient.

[0006] As another example, the invention patent with the Chinese patent publication number CN1920803A discloses a processor whose communication interface includes communication with an expansion module so as to read and write discrete input / output, analog input / output, intelligent module control, and expansion module status. The serial communication method of the dedicated ASIC also has many serial communication leads, and a dedicated single-chip microcomputer is required to be matched with an ASIC to realize the function of the expansion module, resulting in a high cost of using the expansion module

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