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This article mainly introduces what the microprocessor is in the microcomputer, the article is very detailed, has a certain reference value, interested friends must read it!

In a microcomputer, an arithmetic unit and a controller are collectively called "microprocessors". Microprocessor A central processing unit consisting of one or a few large-scale integrated circuits; generally speaking, microprocessor chips are integrated with controllers, calculators, registers and internal buses that connect them.

A central processing unit consisting of one or a few large-scale integrated circuits. These circuits perform the functions of the control unit and the arithmetic logic unit.

Generally speaking, microprocessor chips are integrated with controllers, calculators, registers and internal buses that connect them.

The microprocessor can complete the operations such as fetching instructions, executing instructions, and exchanging information with external memory and logic components, so it is the operation control part of the microcomputer. It can form a microcomputer with memory and peripheral circuit chips.

Composition

The microprocessor consists of arithmetic logic unit (ALU,Arithmetic Logical Unit), accumulator and general register set, program counter (also called instruction indicator), timing and control logic unit, data and address latch / buffer, and internal bus. Among them, the arithmetic unit and controller are the main components.

Arithmetic logic unit

The arithmetic logic unit ALU mainly performs arithmetic operations (+, -, ×, /, comparison) and various logic operations (and, OR, non, XOR, shift) and so on. ALU is a combinational circuit, which does not have the function of registering operands, so it must have two registers to save operands: register TMP and accumulator AC. The accumulator not only provides operands to ALU, but also receives the results of ALU operations.

The register array is actually equivalent to the RAM in the microprocessor. It consists of two parts: the general register group and the special register group. The general register is used to store the data, intermediate results or addresses that participate in the operation. They can generally be used as two 8-bit registers. With these registers in the processor, frequent access to memory can be avoided, instruction length and execution time can be shortened, the running speed of the machine can be improved, and programming will be convenient. Special registers include program counter PC, stack indicator SP and flag register FR. Their functions are fixed and are used to store addresses or address bases. Where:

A) the program counter PC is used to store the address of the next instruction to be executed, so it controls the order in which the program is executed. Under the condition of sequential execution of instructions, each byte of the instruction fetched, the content of the PC is automatically increased by 1. When a program is transferred, the new instruction address (target address) must be loaded into the PC, which is usually achieved by the transfer instruction.

B) the stack indicator SP is used to store the top address of the stack. A stack is a specific area of memory. It works according to the "last-in-first-out" mode. When the new data is pressed into the stack, the original information in the stack remains unchanged, only the position at the top of the stack is changed. When the data pops up from the stack, it pops up the data at the top of the stack, and automatically adjusts the position at the top of the stack after popup. In other words, the data is always carried out at the top of the stack when the data is pressed and unstacked. Once the stack is initialized (that is, the location of the bottom of the stack in memory is determined), the contents of the SP (that is, the location of the top of the stack) are automatically managed by CPU.

C) the flag register, also known as the program status word (PSW) register, is used to store the result characteristics of arithmetic and logic operation instructions, such as carry or overflow flags when the result is 0.

Timing and control logic is the core control component of the microprocessor, which is responsible for controlling the whole computer, including fetching instructions from memory, analyzing instructions (that is, instruction decoding) to determine instruction operations and Operand addresses, taking operands, performing operations specified by instructions, and sending operation results to memory or Igamo port, etc. It also sends corresponding control signals to other parts of the microcomputer to make the internal and external parts of the CPU work harmoniously.

The internal bus is used to connect the functional components of the microprocessor and transmit the data and control signals inside the microprocessor.

It must be pointed out that the microprocessor itself can not constitute an independent working system, nor can it execute programs independently. It must be equipped with memory and input and output devices to form a complete microcomputer before it can work independently.

Storage device

The memory of a microcomputer is used to store programs and data that are currently in use or are often used. Memory is divided into random access memory RAM (Random Access Memory) and read-only memory ROM (Read only Memory) according to read and write mode. RAM, also known as read / write memory, CPU can read or write its contents at any time as needed. RAM is a volatile memory, that is, all its contents will be lost after a power outage, so it can only store temporary programs and data. The contents of ROM can only be read out but not written, and the stored information remains unchanged after power off, so it is a non-volatile memory. So ROM is often used to store permanent programs and data. Such as the initial guidance program, monitoring program, the basic input in the operating system, output management program BIOS and so on.

Ipaw O interface

Input / output interface circuit is an important component of microcomputer. It is a logic control circuit for a microcomputer to connect external input and output devices and various control objects and exchange information with the outside world. Because the structure, working speed, signal form and data format of the peripherals are different, they can not be directly connected to the system bus. The input / output interface circuit must be used for intermediate conversion in order to realize the information exchange with CPU. The Ithumb O interface is also known as the Ithumb O adapter, and different peripherals must be equipped with different Imax O adapters. Icano interface circuit is an indispensable and important part of microcomputer application system. In fact, the development and design of any microcomputer application system is mainly the development and design of Imax O interface. Therefore, the Icano interface technology is one of the important contents discussed in this course, which we will introduce in detail in Chapter 8.

Bus

Bus is a common channel for transmitting information between components in a computer system, and it is an important component of a microcomputer. It consists of several communication lines and various tristate gate devices that drive and isolate. In the form of structure, the microcomputer always adopts the bus structure, that is, the functional components of the microcomputer (microprocessor, memory, I hand O interface circuit, etc.) are connected by bus, which is the unique feature of the microcomputer system structure. After adopting the bus structure, the relationship between the functional components in the system is transformed into a single bus-oriented relationship among the components. As long as a component (function board / card) meets the bus standard, it can be connected to the system using this bus standard, so that the system function can be easily expanded or updated, the structure is simple, and the reliability is greatly improved. In microcomputers, according to their location and application, the bus can be divided into the following four levels, as shown in figure 1.4.

(1) on-chip bus: it is located inside the microprocessor chip, so it is called on-chip bus. It is used for the interconnection and information transmission between ALU and various registers in the microprocessor (for example, the internal bus in figure 1.3 is the on-chip bus). Due to the limitation of chip area and the number of external pins, most of the on-chip buses adopt single-bus structure, which is beneficial to the improvement of chip integration and yield. If the speed of internal data transmission is required, double-bus or three-bus structure can also be adopted.

(2) Chip bus: chip bus is also called component level (chip level) bus or local bus. The microcomputer motherboard, single trigger and some other plug-in boards and cards (such as various Iram O interface boards / cards) are themselves a complete subsystem. The board / card contains various chips such as CPU,RAM,ROM,I/O interface, and these chips are also connected by bus, because it helps to simplify the structure, reduce the connection, improve the reliability, and facilitate the transmission and control of information. The buses on various boards and cards that realize the interconnection between chips are usually called chip buses or component-level buses.

Compared with a complete microcomputer, all kinds of boards / cards are only a subsystem and a part, so the chip bus is called the local bus, and the bus used to connect the functional components of the microcomputer is called the system bus. Local bus is an important concept, which we will discuss in Chapter 7.

(3) Internal bus: internal bus is also called system bus or board-level bus. Because the bus is used to connect the functional components of the microcomputer to form a complete microcomputer system, as shown in figure 1.2, it is called the system bus. The system bus is the most important bus in the microcomputer system. People usually refer to the system bus, such as PC bus, AT bus (ISA bus), PCI bus and so on. System bus is one of the key contents that we want to discuss.

The information transmitted on the system bus includes data information, address information and control information. Therefore, the system bus contains three kinds of buses with different functions, namely, data bus DB (Data Bus), address bus AB (Address Bus) and control bus CB (Control Bus), as shown in figure 1.2.

The data bus DB is used to transmit data information. The data bus is a bi-directional three-state bus, that is, it can not only transfer the data of CPU to other components such as memory or Icano interface, but also transfer the data of other components to CPU. The number of bits of the data bus is an important index of the microcomputer, which is usually consistent with the word length of the microprocessor. For example, the word length of the Intel 8086 microprocessor is 16 bits, and its data bus width is also 16 bits. It should be pointed out that the meaning of data is in a broad sense. It can be real data, instruction code or status information, and sometimes even a control information. Therefore, in practical work, what is transmitted on the data bus is not necessarily just the real data.

The address bus AB is specially used to transmit addresses. Because addresses can only be transferred from CPU to external memory or I _ Universe O port, the address bus is always one-way and three-state, which is different from the data bus. The number of bits of the address bus determines the directly addressable memory space of the CPU. For example, if the address bus of an 8-bit microcomputer is 16 bits, the maximum addressable space of the 16-bit microcomputer is 2 ^ 16 = 64KB, the address bus of the 16-bit microcomputer is 20 bits, and the addressable space is 2 ^ 20 = 1MB. In general, if the address bus is n bits, the addressable space is 2 ^ n bytes.

The control bus CB is used to transmit control signals and timing signals. Among the control signals, some are sent by the microprocessor to the memory and the Imax O interface circuit, such as read / write signal, chip selection signal, interrupt response signal, etc., and some are fed back to the CPU by other components, such as interrupt request signal, reset signal, bus request signal, limit ready signal and so on. Therefore, the transmission direction of the control bus is determined by the specific control signal, which is generally bi-directional, and the number of bits of the control bus should be determined according to the actual control needs of the system. In fact, the specific situation of the control bus mainly depends on the CPU.

(4) external bus: also known as communication bus. It is used for the connection and communication between two systems, such as between two microcomputer systems, and between microcomputer systems and other electronic instruments or electronic devices. The commonly used communication buses are IEEE-488 bus, VXI bus and RS-232 serial bus. The external bus is not inherent in the microcomputer system itself, but only in the microcomputer application system.

The above is all the contents of the article "what is a microprocessor in a microcomputer". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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