The basic structure and working principle of embedded programming microcontroller

This series explains the basics necessary for an embedded system development technician. This basic knowledge is a common technical knowledge that both hardware and software technicians should master. With the basic knowledge of electronic circuits and digital circuits, you can begin to learn the core components of embedded systems - microcontrollers. In this article, we will introduce you to the basics of microcontrollers.

In the introduction series of the single-chip microcomputer, first learn the basic structure and working principle of the single-chip microcomputer, as well as the peripheral function circuit, and then challenge the operation of an actual single-chip microcomputer.

The basic structure and working principle of embedded programming microcontroller

The one-chip computer is the brain that controls the electronic products.

Today, many of the appliances in our lives use microcontrollers. For example: mobile phones, televisions, refrigerators, washing machines, and children's toys that flash when the LEDs are pressed. So, what exactly did the microcontroller do in these appliances?

The one-chip computer is the key to the action of these electrical appliances, and it is the command hardware operation. For example, the input signal of the button or button is received, and the peripheral function circuit of the motor and the LCD is commanded according to a pre-programmed program.

So, how is the microcontroller formed? (figure 1)

The MCU is composed of CPU, memory, peripheral functions and other parts. If the microcontroller is compared to a human, then the CPU is responsible for thinking, the memory is responsible for memory, and the peripheral functions are equivalent to the visual sensory system and the nervous system that controls the movement of the hands and feet.

Figure 1: Components of a microcontroller

Figure 1: Components of a microcontroller

Although we say that the CPU is equivalent to the human brain, it cannot be consciously and spontaneously thought like the human brain. The CPU can only read and execute the instruction combinations (programs) stored in advance in memory. Of course, the instructions executed by the CPU are not high-level commands such as "walking" or "speech", but some very simple instructions, such as "reading data" from somewhere in memory or "writing" some data into memory. Somewhere, or add, multiply, and logical operations, and so on. However, the combination of these simple instructions can achieve many complex functions.

CPU that will think

Let us understand the role of the CPU from its composition. (figure 2)

Figure 2: The role of the CPU

Figure 2: The role of the CPU

Program counter

When the CPU reads the instruction, it needs to know where the instruction to be executed is stored in the memory. This location information is called the address (equivalent to the home address). The program counter (PC) is the register that stores the address. Usually, the PC is designed to increment by 1, that is, when the CPU executes the instruction in the 0000 address, the PC automatically increments by 1 to become the 0001 address. Each time an instruction is executed, the PC will automatically increment by one to point to the address of the next instruction. It can be said that the PC determines the order in which the programs are executed.

â—‡ instruction decoding circuit

The instruction decode circuit is the meaning of interpreting the instructions read from the memory. The arithmetic circuit operates according to the decoding result. Specifically, the instruction decoding circuit is the decoding circuit we learned in "Getting Started with Digital Circuits (2)", but the circuit structure is slightly more complicated. Therefore, the working principle of the instruction decoding circuit is from being symbolized (encrypted). In the instruction, restore the instruction.

â—‡ arithmetic circuit

The arithmetic circuit is also called ALU (ArithmeTIc and Logic Unit) and is a circuit that completes the operation. It can perform arithmetic operations such as addition, multiplication, etc., and can also perform logical operations such as AND, OR, and BIT-SHIFT. The operation is performed under the control of the instruction decoding circuit. Usually the composition of the arithmetic circuit is complicated.

â—‡CPU internal register

The CPU internal registers are places where temporary information is stored. There are general-purpose registers that store operation values ​​and operation results, and some special registers, such as flag registers that store operation flags. That is to say, when the arithmetic circuit performs the operation, it does not directly operate in the memory, but copies the data in the memory to the general-purpose register and performs the operation in the general-purpose register.

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