With the emergence of the domestic super-large scale integrated circuits, microprocessors and peripheral chips has been rapid development. Integration technology is one of the latest developments in the CPU and peripheral chips, such as program memory, data memory, parallel I / O ports, serial I / O ports, timer / counter, interrupt controller and other control components in a single chip of the , the made-chip computer (Single-Chip Microcomputer). In recent years launched a number of high-end microcontroller also includes many special functional unit, such as the A / D, D / A converters, modems, communications controller, PLL, DMA, floating point unit, PWM control output unit, PWM the output when the dead-programmable control functions. Therefore, as long as necessary, along with some expansion of the channel interface circuit and can be formed a variety of computer application systems, such as industrial production line control systems, household appliances, as the main controller, distributed control system, the terminal node or as part of its master control node from the Following the role of data acquisition systems, automatic test systems, etc. [2]. 

SCM, and have been in various technical fields such rapid development, and SCM systems constitute a computer applications related to the formation of the following characteristics: 

    2.1, single-chip computer application systems have greater reliability. The reliability of access in addition to their high reliability microcontroller chip itself and the application of at least connection, but also can easily use the software and hardware technology. 

   2.2, system expansion, system configuration more typical, standardized, easy to create various size applications, the application system has a higher hardware and software utilization factor. 

   2.3, due to the application constitutes a system is a computer system, a considerable number of measurement, control function is performed by software, it has flexible features, no need to change the hardware system will be able to change the system functions properly. 

   2.4, has excellent performance price ratio. 

Can be said that facing the MCU application technologies at home and abroad, as the 60's transistor technology faces 70 years to face the same digital integrated circuits. Microcontroller and programmable gate arrays combine to form a new generation of electronic applications and technology are impossible to evade a new type of engineering application of technology  

    AT89S52 is a kind of 4K bytes of flash erasable programmable read-only memory (FPEROM-Flash Programmable and Erasable Read Only Memory) of the low-voltage, high-performance CMOS 8-bit microprocessors, commonly known as microcontrollers. AT89C2051 is a kind of 2K bytes of flash erasable programmable read only memory of the microcontroller. MCU EEPROM erasure can be repeated 100 times. The device uses high-density non-volatile memory ATMEL manufacturing technology manufacturing, and industry-standard MCS-51 instruction set and output pins are compatible. Owing to the multi-function 8-bit CPU and flash memory combined in a single chip, ATMEL The AT89S52 is a highly efficient micro-controller, AT89C2051 is a streamlined version of it. AT89C SCM for many embedded control system provides a high degree of flexibility and inexpensive solution. 

Pin Description: 

    P0 port: P0 port as an 8-bit open drain bi-level I / O port, each pin can absorb 8TTL gate current. When the P1 port pin for the first time to write 1, is defined as high-impedance input. P0 can be used for external program data memory, which can be defined as data / address of the eighth. The FIASH programming, P0 port input as the original code, when FIASH to verify when, P0 output of the original code, this time must be pulled outside P0. 

   P1 port: P1 port is an internal pull-up resistor to provide 8-bit bi-directional I / O port, P1 port buffer to receive the output 4TTL gate current. P1 port pin to write a post, was the internal pull-high, can be used as input, P1 port is an external pull-down low, the output current, which is due to internal pull-up's sake. In the FLASH programming and verification time, P1 port as the eighth-bit address to receive. 

   P2 port: P2 port for an internal pull-up resistor 8-bit bi-directional I / O port, P2 port buffer can receive the output 4 TTL gate current, when the P2 port is to write "1", its pin is internal pull-up resistors, and as input. And therefore, as input, P2 port pins are externally pulled low, the output current. This is due to internal pull-up's sake. P2 port when used with an external program memory or 16-bit addresses to access external data memory, when, P2 port output address high 8. In the given address "1" when it uses the internal pull-up edge, when the address of the external data memory read and write eight hours, P2 port output the contents of its special function register. P2 population in the FLASH programming and verification time to receive high eight address signals and control signals. 【转载请注明出处：https://www.5ubs.com/bsTemplate/fanyi/538.html】