Programmable controller of the hardware and software in detail

Programmable controller Originally should be referred to as the PC, personal computer designed according to the PC in order to distinguish, so (referred to as PLC programmable controller) , but is not to say that PLC can only control logic signal. PLC is designed for industrial environment applications, with intuitive, simple and easy to master a programming language environment of industrial field control unit. The basic component of PLC and PLC basic components include the CPU ( CPU) , memory, input/output interface ( Abbreviation for I/O, including input interface, output interface, external device interface, extension interface, etc. ) And external device programmer and the power supply module, as shown in figure 1. Between PLC inside each unit through the power bus, control bus, address bus and data bus connection, the exterior was based on the actual control object configuration corresponding device and a control device of PLC control system. Figure 1 the basic component of PLC and 1. Central processing unit (CPU), the central processor, CPU) Consists of controller, arithmetic unit and registers and integrated on a chip. CPU bus through data bus, address bus and control bus and power bus and memory, input/output interface, programming device and the power supply is connected. Small PLC CPU USES 8 bit or 16 bit microprocessor or microcontroller, such as 8031, M68000, this kind of chip price is very low; Medium-sized PLC CPU adopts 16-bit or 32-bit microprocessor or microcontroller, such as 8086, 96 series single chip microcomputer, this kind of chip main characteristic is high integration, fast speed and high reliability; Large PLC will be expected to adopt high-speed processor slice weakness. CPU according to the function of the command given by the PLC system program in PLC control system to finish the work tasks. 2. Memory in the PLC memory is mainly used for storing system program, the user program and data, etc. 1) PLC system program memory system determines the basic functions of the PLC program, the part program written by PLC manufacturer (s) and curing in the system program memory, there are mainly the hypervisor, user command interpreter and function program and the system call. It mainly controls the operation of the PLC system management program, PLC according to the order of the right to work; User command interpreter will PLC user instructions into machine language, transferred to the CPU execution; Function program and the system call is responsible for calling the function of different subroutines and management procedures. System program belongs to the important data to long-term preservation, so its use ROM or an EPROM memory. ROM is read only memory, the memory can only read the content, can't write content, ROM is non-volatile, which can save the content of the stored power disconnect. EPEROM to erase read-only memory, must use ultraviolet irradiation on the chip lens window to erase the content written, electric erasing programmable read-only memory still have E2PROM chips was introduced, FLASH, etc. 2) User program memory user program memory used to store the user load of PLC application, load the initial user program because of the need to modify and debug, so called user debugger, in within the RAM random access memory can be random read and write operations to facilitate the user to change and debugging. After modification and debugging the program is called the user performs, because do not need to modify and debug, so users perform program was solidified in the EPROM for long-term use. 3) The PLC data storage to be generated during the operation, or call the intermediate results data ( Such as the state of the input/output element data, timers, counters, preset value and current value, etc. ) And the configuration data ( Configuration, set the input filter such as input and output, pulse trapping and output table configuration, define scope of storage area to keep configuration, analog potentiometer Settings, high-speed counter, high-speed pulse output configuration, communication configuration, etc. ) In working, this kind of data stored in data storage, because the working data and configuration data is constantly changing, and do not need to save for a long time, so the RAM random access memory. RAM is a kind of high density, low power consumption of semiconductor memory, lithium battery as backup power supply are available, and once the power can be through the lithium battery power supply, keep the contents of the RAM. 3. Interface input and output interface is PLC and industrial control or testing components and actuators connected interface circuit. PLC input interface such as dc input, ac input, ac/dc input types; Output interface has the transistor output and thyristor output and relay output type. Type transistor and brake pipe output for contactless output circuit, a transistor output type used in high frequency low power load, thyristor output model used in high frequency high power load; Relay output to have contact output circuit, used for low frequency load. Field control or input of PLC control signal detecting element, such as limit switch, button, switch, and other operation of sensor output switch or analog, etc. , and through the input interface circuit converts the signals into the CPU can receive and process the signal. Send the CPU output interface circuit of low voltage control signal is converted into the field to the high voltage signal output, to drive the solenoid valve, contactor is accused of equipment such as actuators. 1) Input interface used to receive input interface, and two types of input signal sampling, one kind is by the button, switch, trip switch, relay contacts the top switch quantity input signal; Another kind is provided by the potentiometer, tachogenerator and various converter continuous variation of the analog input signal.