Programmable controller of hardware system, Figure)

The simplified diagram of figure 1 PLC hardware system of the structure diagram of programmable controller and computer is the same, by the central processor ( CPU) , memory and input/output interface, etc. Therefore, from the hardware structure, the programmable controller is in fact the computer, figure 1 is a simplified block diagram of the hardware system. Can be seen from the diagram of PLC internal main components are: ( 1) CPU ( 中央处理单元) The CPU is the core component of PLC, and general microcomputer CPU, the role of it in PLC system is similar to the nerve center of human body, so called 'computer'. Its features are: a, according to the function of PLC system program gives in, & # 127; Receive and storage from programmer input of the user program and data. B, receive scan mode with the state of the input device type data, and in the image or data registers. C, diagnosing the working state of the circuit inside the power supply, PLC and programming in the process of grammatical errors. D, the arrival of PLC in running state, to read a detailed user program from memory, after command interpretation task, as stipulated in the instructions produced the corresponding signal, to open/close the control gate. Points at the channel to perform data access, transmit, combination, comparison and transformation, such as operation, complete the logic type specified in the user program arithmetic operations such as task. According to the results of the operation state of updates on logo position and output image, the contents of a register again by the output image of a status type data registers the related content, realize the output control, tabulation, print, data communication, etc. Commonly used PLC CPU mainly adopts general microprocessor, microcontroller, or bipolar slice decay processor. Common microprocessors commonly used 8-bit and 16-bit machine, such as Z80A, 8085, 8086, 6502, M6800, M6809, M68000, etc. Commonly used microcontroller 8039, 8049, 8031, 8051, etc. Bipolar slice commonly used have AMD2900 processor, AMD2903, etc. (1) using general microprocessor as the CPU in low-grade PLC, made CPU is relatively common, Z80A Z80A for PLC has the following advantages: Z80 ( Or Z80A) CPU chips and cheap, popular, general motors, made of PC, the chip bring convenient maintenance and popularization. Z80 has independent of the input/output instructions and instruction format is shorter, the & # 127; Execution time is shorter, conducive to scan cycle shortened. Z80 input/output instruction format is shorter, the corresponding input/output devices coding is short, so the corresponding decoding hardware device is relatively simple. Because Z80 is using the input/output mapping information, so that the design flow, program for addressing to the difference between input/output and storage. (2) using single chip as the CPU since 1974 single chip microcomputer, the & # 127; There have been many products for programmable controller by single chip microcomputer. Japan's mitsubishi series PLC is used F the INTEL company MES - 48 do processor series of single-chip microcomputer 8049 and 8039, 8039 single chip microcomputer in a piece of film used 8-bit CPU, & # 127; 128 x 8 data storage. Article 27 the input/output lines, T0, T1, INT test line and eight timer/counter, clock oscillation circuit, etc. Since the 80 s, a more integrated. More powerful, and with 'Boolean machine' MCS - and easy for data communication 51 series microcontroller higher 16-bit single chip microcomputer and function, to replace the MCS - 48 series. Japan's mitsubishi F2 CPU8031 series PLC is adopted. MCS - 51 series microcontroller is the INTEL based on single chip microcomputer MCS - 48, the products are carried out in the early 80 s, has high integration, high reliability, high function, high speed, low price, etc. There are three representative products: 8051, 8751 and 8031, they have different application characteristics, respectively. 8051 is 4 k bytes EPR0M instead of 4 k bytes of R0M 8051; 8031 is an internal no R0M8051. Must be an external EPR0M; INTEL 96 series single chip microcomputer, word length is 16, computing speed is higher than 51 series, which will bring high grade PLC development and application of good vision. Made of single chip microcomputer PLC has the following marked characteristics: create conditions for the integration of mechanical and electrical equipment, because made by single chip microcomputer PLC, smaller. PLC logic function is very strong at the same time, and with numerical computation and communication interface. (3) made CPU slice slice decay processor decline the processor's main features are: high speed, strong flexibility, & # 127; High efficiency, etc. Can 'cascade', 'line' operation easily.