What is A MCU’s internal Structure: Single Chip Micro-Computer

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Author: Kynix

Published: 2018-09-13 | Last Updated: 2018-09-13

Contents

This article would introduce MCU in details, including analysis its internal structure, and elaborate some important concepts, especially would put emphasis on the concept of memory decoding.

Catalog

I. What is MCU?

II. Some Basic Concepts

2.1 The Meaning of Rom

2.2 The Meaning of Bit

2.3 The Meaning of Bytes

III. The Working Principle of Memory

IV. MCU Circuit

v. Memory Decoding

FAQ

I. What is MCU?

MCU(microcomputer) is an integrated circuit chip. It integrates the microprocessor(CPU), which has data-handling technology such as arithmetic, logic and data transfer, etc, random access data memory(RAM), read-only program memory(ROM), input and output circuit (I/O port) that using the very large scale processing-data technology and may also include a timing counter, serial communication port (SCI), display drive circuit (LCD or LED drive circuit), pulse width modulation circuit (PWM), analog multiplexer and A/D converter, which form a minimum but perfect computer system.

Under the control of software, these circuits can complete the tasks specified by the program designer accurately, quickly, and efficiently. From this point of view, the single-chip microcomputer has the function which the microprocessor does not have, it has intelligent control functions which the modern industry control request separately. And this is the single-chip microcomputer's biggest characteristic.

SCM

II. Some Basic Concepts

2.1 The Meaning of Rom

Let's think about a problem: when we write instruction in a programmer into an MCU and then take off it, the MCU can execute the instruction, so the instruction must be stored somewhere in the MCU. And this place can still maintain this instruction not to be lost after it power-off. What place is this? This place is the internal ROM of MCU, which is the read-only program memory. Why do you call it read-only memory? We use the programmer, external equipment, to write to the ROM operation under special conditions. In the MCU normal working conditions, the data can only read but can’t write in, so we call it ROM.

2.2 The Meaning of Bit

From the experiment above, we already know that the level of a lamp or a line can represent two states: 0 and 1. In fact, this is a binary bit, thus we call a line a bit, expressed in BIT.

2.3 The Meaning of Bytes

A line can represent 0 and 1, two lines can express 00, 01, 10, 11 four states, that is, it can express 0 to 3, and three can express 0 to 7. The computer usually put with eight lines together, counting at the same time, can represent 0 to 255, for a count of 256 states. These eight lines or 8-bit is called a byte (BYTE).

III. The Working Principle of Memory

Structure

All the instructions that a single-chip microcomputer can execute are the instructional systems of it. Different kinds of single-chip computers have different instructional systems. In order for a single-chip microcomputer to automatically complete a specific task, the problems to be solved must be programmed into a series of instructions (these instructions must be recognized and executed by the selected single-chip microcomputer). These instructions integrated into the program, and the program needs to be stored in memory—a storage unit.

The memory consists of many storage units (the smallest unit of storage), just as a building has many rooms, each room in a large building is assigned a unique room number. Each storage unit must also be assigned a unique address number, which is known as the address of the storage unit so that the address of the storage cell is known. The instructions are stored in these units. The storage unit can be found, where the stored instructions can be taken out and then executed.

SCM Sample

Memory is the place where data is stored. It uses the electricity level to store the data, that is, it actually stores the electrical level, not the number of 1234 that we are used to thinking of. A memory is like a small drawer. If there are eight small drawers in a small drawer, each one is used to store the "charge," and the charge is passed in or released through the wire attached to it. You can think of a wire as a pipe, and the charge in the grid is like water, so it's easy to understand it. Each small drawer in memory is a place for data, which we call a ''bit''.

With this structure, we can start storing data. If we want to put in a data 12, that is 00001100, and we just have to fill the second and third squares with the charge, and the other cells are free of the charges. But the problem is that memory has a lot of cells, and the lines are parallel, and when you put the charge in it, you put the charge in all the cells, and when you release the charge, you release the charge from each cell. In the case of it, no matter how many cells the memory has, it can only be put in the same number, which is certainly not what we want.

A little bit to change structurally, there's a control line on each unit, and if you want to put the data in the unit, give a signal to the control line of the unit. Therefore, the control line turns on the switch so that the charge can flow freely. And there is no signal on the other unit control lines, so the switch turns off and will not be affected, so that if you handle the control lines of different units, you can write different data to each unit. Similarly, if you want to take data from one unit, just turn on the corresponding control switch.

IV. MCU Circuit

A circuit is always made up of components connected by wires. In analog circuits, wiring is not a problem, because there is usually a serial relationship between the devices, and there are not many connections between the devices, but the computer circuits are different. The microprocessor is the core for it, each device must be connected to the microprocessor, the work of each device must be coordinated, so it needs a lot of connections.

If still like analog circuits, there will be an amazing number of lines between microprocessors and devices, so the concept of a bus has been introduced into the microprocessor, and each device has shared the connection. All 8 data lines are connected to eight common lines, that is, the equivalent of each device is in parallel, but this is not enough. If there are two devices delivering data at the same time, one is 0 and the other is 1, what exactly does the receiver get? This situation is not allowed, so control through the control line to make the device working time-sharing, at any time there can be only one device to send data ( multiple devices can receive at the same time).

Latch and Interface

V. Memory Decoding

So how do we control the control lines of each unit? It is not that simple to lead the control lines of each unit out of the integrated circuit. There are 65,536 units in a model 27512 memory, and if each line is drawn out, the integrated circuit must have more than 60,000 feet, so it is necessary to find a way to reduce the number of lines. We have a way called decoding, briefly introduce: one line can represent two states and two lines can represent four states and three lines can represent eight kinds, and so on, thus we only need 16 lines to represent 65536 states.

Since the decoding problem solved, let's focus on another problem. Where did the eight lines in each unit come from? Actually, it is connected to the computer, in general, the eight wires not only for memory but also connected to other devices. The problem arises in this way. Because these eight wires are not dedicated to the memory and the computer, it is not good if a unit is always connected to the eight wires. For example, if the value in this memory cell is 0FFH but there one unit is OOH, then what the line set at a high level or a low level?

Thus we have to separate them. The solution is: when the outside wire is connected to the pin of the integrated circuit, it does not directly attach to the units, but a set of switches is added to the middle. Normally we leave the switch off, and if we really want to write data to this memory, or read the data out of the memory, just turn the switch on. This set of switches is selected by three leads: read control, write control, and chip selector.

To write data into the chip, select the chip first, then send a write signal, the switch turns on, and the incoming data (charge) is written into the film chip. If you want to read, select the film chip first, and then send out the read signal, the switch turns on, and the data is sent out. The read and write signals are also connected to another memory at the same time, but the chip selector ends are different.

Although there is a read or write signal, there is no chip selection signal, so the other memory will not "misunderstand" and result in a conflict. What will happen if you pick two chips at the same time? Actually, this can’t be happening because the system is designed and controlled by computer, not by the human. If any, there’s something wrong with the circuit.

MCU Sample

From the introduction above, we have seen that the eight lines used to transmit data are not dedicated, but shared by many devices, so we call it data bus. The data line of the device is called the data bus, and all the control lines of the device are called the control bus. There are memory cells in the internal or external memory and other devices of a single chip. Units must be assigned addresses before they can be used. Of course, the assigned addresses are also given in the form of electrical signals. Because there are too many memory cells, there are many lines for address allocation, which are called address buses. Sixteen address lines are also connected, called address buses.

FAQ

1. What are the characteristics of microcomputer?

a. Small size and low cost.

b. One user.

c. Easy to use.

d. Low computing power.

e. Commonly used for personal application.

2. What are the advantages of microcomputer?

a. This computer is widely used today.

b. The microcomputer is small in size.

c. The microcomputer is used to design different software and app.

d. This type of computer is a low cost, so all the users can easily buy.

e. No need for highly trained staff for operating microcomputer to office work.

3. Why microcontrollers are often called single chip computers?

Single-chip computers are mainly of the form known as Microcontroller chips (the most commonly known are the PIC range by Microchip inc) and used in embedded devices. They provide much more basic functionality but are far simpler to work with as they don't require any external chips in order to function.

4. What is single chip microcomputer that has everything inbuilt?

This is a microcomputer built using separate components (CPU, Memory, etc.). ... For some specific applications, we also have single chip computers in a VLSI chip. This single chip microcomputer will have a CPU, memory and I/O interfaces, timers, ADC/DACs etc. on a single chip itself.

5. What is difference between microprocessor and microcomputer?

The main difference between Microprocessor and Microcomputer is that the Microprocessor is a computer processor contained on an integrated-circuit chip and Microcomputer is a small, relatively inexpensive computer. ... Microprocessors contain both combinational logic and sequential digital logic.

6. Is Raspberry Pi a microcomputer?

The Raspberry PI is a microcomputer that's often used by hobbyists to create projects like animated LED displays or bird watchers.

7. Which is a feature of a single chip microcomputer?

A single-chip microcomputer is a major branch of a microcomputer. The biggest feature of the structure is that the CPU, memory, timer and various input/output interface circuits are integrated on a very large-scale integrated circuit chip. In terms of its composition and function, a single chip is a computer.

8. What are the components of microcomputer?

The main components are: (1) the central processing unit (CPU), (2) input devices, (3) output devices, and (4) memory. The CPU of a microcomputer performs all the arithmetic, logic, and data handling functions of the microcomputer.

9. Is microcontroller a microcomputer?

A Microcontroller is a small and low-cost microcomputer, which is designed to perform the specific tasks of embedded systems like displaying microwave information, receiving remote signals etc.

10. What is the definition of microcomputer?

Microcomputer, an electronic device with a microprocessor as its central processing unit (CPU). Microcomputer was formerly a commonly used term for personal computers, particularly any of a class of small digital computers whose CPU is contained on a single integrated semiconductor chip.

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