Electronics

Introduction

Single-Chip Microcomputer (Microcontrollers/SCM) is a kind of integrated circuit chip, which uses VLSI technology to integrate the central processing unit CPU with data processing capabilities, random access memory RAM, read-only memory ROM, various I/O ports, interrupt systems, and timer /Counter and other functions (may also include display drive circuit, pulse width modulation circuit, analog multiplexer, A/D converter and other circuits) integrated into a silicon chip to form a small and complete microcomputer system, widely used in the field of industrial control. From the 1980s, it developed from the 4-bit, 8-bit microcontroller to the current 300M high-speed microcontroller.

Basic Structure

• Arithmetic Unit

Arithmetic Unit is composed of arithmetic logic unit (ALU), accumulator and register. The function of ALU is to perform arithmetic or logical operations on the incoming data. The input comes from two 8-bit data sources, one from the accumulator and the other from the data register. ALU can perform various operations on the data, such as Addition, Subtraction, AND, OR, Comparison, etc., and finally store the results in the accumulator.

The arithmetic machine has two functions:

• Perform various arithmetic operations.
• Perform various logical operations and perform logical tests, such as a zero-value test or a comparison of two values.
• All operations performed by arithmetic unit are directed by the control signal issued by the controller, and an arithmetic operation produces an operation, and a logical operation produces a decision.

• Controller

Controller is composed of program counter, instruction register, instruction decoder, timing generator and operation controller, etc. It is the "decision-making body" of issuing commands, namely coordinating and directing the operation of the entire microcomputer system. Its main functions are：

• Extract an instruction from memory and indicates the location of the next instruction in memory.
• Decode and test the instructions,then generate the corresponding operation control signal to facilitate the execution of the specified actions.
• Direct and control the direction of data flow between CPU, memory, and input/output devices.

Microprocessor interconnects ALU, counter, register and control parts through an internal bus, and connects the external memory, input and output interface circuit through an external bus. External bus, also known as system bus, is divided into data bus DB, address bus AB and control bus CB. It can be connected with various peripheral devices through the input and output interface circuit.

Primary Register

• AccumulatorA
  AccumulatorA is the most frequently used register in the microprocessor. It has dual functions in arithmetic and logic operations: it is used to save an operand before operation; After operation, it is used to save the result of sum, difference or logical operation.

• Data register DR
  Data register is a temporary storage unit that sends (writes) or fetches (reads) data to memory and input/output devices through the data bus. It can save an instruction being decoded, or a data byte being sent to memory for storage, etc.

• Instruction register IR and Instruction decoder ID
  Instructions include opcodes and operands. The instruction register is used to save an instruction currently being executed. When an instruction is executed, it is first taken from memory to the data register, and then transferred to the instruction register. When the system executes a given instruction, it must decode the operation code to determine the required operation. The instruction decoder is responsible for this work. The output of the opcode field in the instruction register is the input of the instruction decoder.

• Program counter PC
  PC is used to determine the address of the next instruction to ensure that the program can be executed continuously, so it is usually called the instruction address counter. Before program execution, the memory unit address of the first instruction of the program (that is, the first address of the program) must be sent to the PC so that it always points to the address of the next instruction to be executed.
• Address register AR
  The address register is used to store the address of the memory unit or IO device to be accessed by the current CPU. Because of the speed difference between memory and CPU, address registers must be used to keep the address information until the memory read and write operations are completed.

Obviously, when the CPU stores data to the memory, fetches data from the memory, and reads instructions from the memory, the address register and data register are used. Similarly, if the address of the peripheral device is regarded as the memory address unit, the address register and data register are also needed when the CPU and the peripheral device exchange information.

Hardware Feature

The volume of the Single-chip Microcomputer(SCM) is relatively small. As a computer system, the internal chip has simple structure, perfect functions, and is very convenient to use. It can be used in a modular way.

• SCM has a high degree of integration and reliability. Even if the single chip microcomputer is working for a long time, there will be no failure problem.
• Low voltage and low energy consumption in the application of SCM is the first choice in people's daily life, providing convenience for production and research and development.
• SCM has strong data processing ability and computing ability, can be used in various environments, and has strong control ability

Development of SCM Technology

The development of SCM in electronic technology mainly includes CPU development, program development, memory development, computer development and C language program development. At the same time, the development can ensure that the SCM can be carried out normally and orderly in a very complex computer and control environment, which requires relevant personnel to take certain measures:

• CPU development.The development of the CPU bus width in the SCM can effectively improve the slow information processing function of the microcontroller, improve the efficiency and speed of information processing, develop and improve the actual structure of the central processor, which can run 2-3 CPU at the same time, thus greatly improving the overall performance of the SCM.
• Program development. The reasonable application of embedded system has been vigorously promoted. When developing programs, it is required to automatically execute various instructions, so that external data can be collected quickly and accurately, and the application efficiency of single-chip microcomputer can be improved.
• Memory development. The development of SCM should focus on memory, and strengthen the exploration of new memory based on the traditional memory read and write function, so that it can achieve both static read and write and dynamic read and write, thus significantly improving the storage performance.
• Computer development. Further optimize and develop SCM stress analysis, and apply computer system to realize data transmission by connecting communication data.
• C language program development. The optimized development of C language can ensure that the SCM can be carried out normally and orderly in a very complex computer and control environment, and promote its wide and comprehensive application.