[2022] What is a Microcontroller: Definition, Composition and Classification

Do you know the CAN bus? As we know the key technology of it includes two aspects, hardware and software. The hardware includes: microcontroller, CAN controller and CAN transceiver. And the software includes CAN bus network application layer protocol and the node control program.

The microcontroller is an important hardware component of the CAN bus. In this article, we will explain in detail the different types of microcontrollers.

1 What is a Microcontroller: Definition

MCU is called Microcontroller Unit. Since the microcontroller integrates the arithmetic logic unit (ArithmeTIc Loaic Unit.ALU), memory, timer/calculator and various I/O circuits into one chip to form a basically complete computing system, it is also called Single-chip microcomputer (Single-Chip Microcomputer).

The program in the microcontroller memory is used closely with the microcontroller hardware and peripheral hardware circuits. It is different from the software of the PC. The program of the microcontroller is called firmware (Firmware). Generally speaking, a microprocessor means that the CPU is on a single integrated circuit, and a microcontroller means that the CPU, ROM, RAM, VO, timer, etc. are all on a single integrated circuit.

Compared with the CPU, the microcontroller does not have such powerful computing power, nor does it have a memory management unit (Memory Manaaement Unit, MMU), which makes the microcontroller only handle some relatively single and simple tasks such as control and logic. It is used in equipment control, sensor signal processing and other fields, such as some household appliances, industrial equipment, electric tools, etc.

2 What is a Microcontroller: Composition

One microcontroller consists of a CPU (central processing unit), memory, and input/output:

·CPU:

The central processing unit is the core component of the MCU, including two main parts of the arithmetic unit and the controller.

1. calculator

The arithmetic unit is composed of several parts such as arithmetic logic unit (Arithmetic & Logical Unit, referred to as ALU), accumulator and register. The role of the ALU is to perform arithmetic or logic operations on the incoming data. The input source is two 8-bit data, which come from the accumulator and the data register respectively. The ALU can perform operations such as addition, subtraction, AND, or, and comparison of the two data, and finally store the result in the accumulator.

The calculator has two functions:

(1) Perform various arithmetic operations.

(2) Perform various logical operations and perform logical tests, such as zero-value testing or comparison of two values.

All operations performed by the arithmetic unit are commanded by control signals sent by the controller, and an arithmetic operation produces an operation result, and a logic operation produces a judgment.

2. controller

The controller is made up of program counter, instruction decoder, , instruction register, timing generator and operation controller, etc. It is the "decision-making mechanism" that issues commands, that is, coordinates and directs the operation of the entire microcomputer system. Its main functions are:

(1) Take an instruction from memory and note the location of the next instruction.

(2) Decode and test the instructions, and generate corresponding operation-control signals

(3) Command and control the data-flow between CPU, memory and input and output devices.

The microprocessor interconnects the ALU, counters, registers and control parts through the internal bus, and connects with the external memory and input and output interface circuits through the external bus. The external bus is also called the system bus, which is divided into data bus DB, address bus AB and control bus CB.

·Memory

Memory can be divided into two categories: data memory and program memory.

The data memory is used to save data, and the program memory is used to store programs and parameters.

· Input/Output - link or drive different devices

Serial communication port - exchange data between MCU and peripherals like UART, SPI, 12C.

3 What is a Microcontroller: Classification

From the number of digits, microcontrollers can be divided into: 4-bit, 8-bit, 16-bit, and 32-bit. In practical applications, 32 bits account for 55%, 8 bits account for 43%, 4 bits account for 2%, and 16 bits account for 1%.

It can be seen that 32-bit and 8-bit microcontrollers are the most widely used microcontrollers today.

The difference in the number of digits cannot represent the quality of the microprocessor. It is not that the microprocessor with the higher the number of digits is better, nor is it that the microprocessor with the lower the number of digits is worse.

8-bit MCUs are versatile; they offer easy programming, energy efficiency, and small package sizes (some as few as six pins). But these microcontrollers are not usually used to implement network and communication functions.

The most common network protocols are 16-bit or 32-bit. Communication peripherals are available for some 8-bit devices, but 16- and 32-bit MCUs are often more efficient choices. Nonetheless, 8-bit MCUs are commonly used in a variety of control, sensing, and interface applications.

In terms of architecture, microcontrollers can be divided into two categories: RISC (Reduced Instruction Set Computers, reduced instruction set computers) and CISC (Complex Instruction Set Computers, complex instruction set computers).

RISC is a kind of microprocessor that executes few computer instructions. It was created from the MIPS host RISC machine in the 1980s. The microprocessors used in RISC machines are referred to as RISC processors. This allows it to perform operations faster (more million instructions per second, or MIPS). Because computers require additional transistors and circuit elements to execute each instruction type, a larger computer instruction set makes the microprocessor more complex and slower to perform operations.

CISC includes a rich set of microinstructions that simplify the creation of programs that run on the processor. Instructions are composed of assembly language. Some commonly used functions originally realized by software are replaced by hardware instruction system, which reduces the work of programmers a lot. At the same time, some low-level operations or calculations are processed in each instruction period to improve The execution speed of the computer, this system is called complex instruction system.

4. What is a Microcontroller: Application

Microcontrollers are usually small and low cost. The selection of each component adheres to the principle of minimizing the volume and minimizing the cost.

• For example, a microcontroller in a TV gets input from a remote control and displays it on the screen. The microcontroller controls the channel selector, speakers and some electronic adjustments of the picture tube such as color, brightness, etc.
• Engine controllers in cars get input from sensors such as oxygen and knock to control things like fuel mixing and spark plug timing.
• The microwave oven controller gets the input signal from the operation keyboard, displays the output on the LCD screen, and controls the relay responsible for the switching of the microwave generator.

Microcontrollers are usually durable, but not always.

For example, a microcontroller that controls a car's engine must be able to operate at temperature extremes that typical computers cannot handle. The microcontroller of a car in Alaska needs to work in a cold weather of minus 34 degrees Celsius, while the same controller needs to work in a hot environment of minus 49 degrees Celsius in Nevada, USA. Coupled with the heat emitted by the engine running, the temperature of the engine box can be as high as 65-80 degrees Celsius above zero.

In many products, such as microwave ovens, the requirements for microcontroller performance are low, and price is the main consideration. In such cases, manufacturers began designing dedicated microcontroller chips—an embedded central processing unit designed for low cost, small size, and low power consumption. The Motorola 6811 and the Intel 8051 are good examples of such chips. There is also a family of controllers called "PIC Microcontrollers" from Microchip that are also very popular. These CPUs are incredibly simple by today's standards; but they are cheap to buy in large quantities, and often only one chip is enough for a product designer's needs.

Further Reading: [Full Guide] How to Select a Microcontroller 2022

5. Summary

One of the serious challenges facing today's automotive electronics engineers is to build a low-cost, trouble-free automotive system that can work even in the event of a failure. As the performance of vehicles is gradually improving, microcontrollers are expected to improve the performance of automotive electronic control units.