INTRODUCTION TO MICROCONTROLLERS

 Central processing unit

the brain of a computer is the central processing unit. it consists of group of circuit that determine the operations that the computer can perform.

CPU component

• arithmetic and logic unit(ALU)
• registers
• instructions register(IR)
• program counter(PC)
• stack pointer(SP)
• instruction decoder and control unit

General block diagram of a CPU

Memory

The memory is used to store data and binary instructions. It is normally organized as several modules (chips), where each module contains several memory locations. Each location may contain part or all of the data or instruction. CPU reads (fetches) the instructions from the memory and performs operations (indicated by instructions) on data.

I/O unit 

 I/O port: 

The hardware in a computer that allows information transfer between the external world and the computer is called I/O port.

 I/O device (Peripherals):

 The device that gives information to the computer is called an input device. For example, keyboard, mouse, joystick, microphone, A/D converters are all input devices. 

 I/O interfacing circuits: 

The circuits that are used to interconnect (interface) I/O devices with a computer or I/O ports are called I/O interfacing circuits. For example, buffers, latches, and voltage level converters are all interfacing circuits. 

System bus 

 Address bus

 It is a group of wires used by CPU to identify specific memory location within a memory chip (also to identify specific memory chip out of many chips present in a computer system) and to identify I/O devices as well. 

 Data bus 

It transfers data or instructions between CPU and memory or I/O devices. It is bidirectional because data can be transferred in both directions i.e. from CPU to memory (or output devices) or from memory or input devices to CPU. 

 Control bus

 It is used to enable memory and I/O devices to perform read or write operations. It regulates all activities on the bus and specifies the timing and direction of the data transfer. Read (RD), write (WR) and memory/ I/O (M/ I/O) are the most common control signals.

MICROPROCESSOR, MICROCOMPUTER AND MICROCONTROLLER 

 Microprocessor 

is a central processing unit (CPU) built into a single semiconductor chip. The structure of microprocessor is same as CPU. 

 Microcomputer 

is a small computer built using microprocessor as a central element. It includes all necessary components required for an application. The I/O devices and memory (types and amount) of a microcomputer are chosen as per the specific application. 

 Microcontroller 

is an entire computer built into a single semiconductor chip. . It includes data and code memory, various on-chip peripherals like timers/counters, serial port, A/D converters, D/A converters, etc, interface controllers, and general purpose I/O ports which allow it to directly interface to external environment.

Comparison between microprocessor and microcontroller

CLASSIFICATION OF MICROCONTROLLERS

  Word length: 

• 4 bit Microcontrollers 

• 8 bit Microcontrollers 

• 16 bit Microcontrollers

 • 32 bit Microcontrollers

 • 64 bit Microcontrollers 

 Memory Architecture: 

• Von Neumann

 • Harvard Architectures 

 Core Architecture: 

• Microcoded 

• Hardwired designs 

 Instruction set architectures:

 • CISC 

• RISC

von Neumann Architecture: 

It has single memory storage to hold both program instructions and data i.e. common program and data space. The CPU can either read an instruction or data from the memory one at a time. The advantage of Von Neumann architecture is simple design of microcontroller chip because only one memory is to be implemented which in turn reduces required hardware. The disadvantage is slower execution of a program.

Harvard Architecture: 

It has physically separate memory storage to hold program instructions and data i.e. separate program and data space. Since it has separate buses to access program and data memory, it is possible to access program memory and data memory simultaneously. The advantage of a Harvard architecture microcontroller is that it is faster for a given circuit complexity because it offers greater amount of parallelism. The disadvantage is that it requires more hardware, because two sets of buses and memory blocks are required.

Microcoded design 

Microcode is a group of instructions used to implement the instructions of a microcontroller/ processor. It resides in a ROM or a programmable logic array (PLA) that is part of the microcontroller chip. The microinstruction is group of bits used to represent the sequence of control signals to fetch, decode and execute the instruction i.e. control signals (in a sequence) for every instruction are generated using memory

Hardwired design 

A hardwired microcontroller/processor uses the bit patterns of the instructions to select and activate specific circuits (may be unique to the each instruction) to execute the instructions. All control signals (or sequence of steps) required to fetch, decode and execute the instructions are generated and controlled by combinatorial logic and state machine circuitry.

CISC: Complex Instruction Set Computer 

 Complex hardware:

 complex as well as more addressing modes, variable instruction size. 

 Many clock cycles to execute an instruction.

 High code density- small program size. 

 Complex data types. 

RISC: Reduced Instruction Set Computer 

 Simple hardware: simple and less addressing modes, fix instruction size. 

 Single clock cycle execution, uniform instruction format. 

 Low code density- Larger program size. 

 Few data types in hardware. 

 Emphasis is on software: Compiler design is more complex.

APPLICATIONS OF MICROCONTROLLERS

  Household appliances: 

Microwave oven, washing machine, 

 Office and commercial appliances: 

Fax machine, photocopier 

 Telecommunication: 

Telephones, phone answering machines, mobile phones 

 Entertainment and gaming:

Televisions,VCRs, music players 

 Automotive industry: 

Fuel injection,ABS 

 Industrial automation and manufacturing:

 Motor control systems, data acquisition and supervisory systems, industrial robots, 

 Electronic measurement instruments:

 Digital multimeters, logic analyzers 

 Biomedical systems: 

ECG recorder, blood cell analyzers 

 Computer systems: 

Keyboard controller, CD drive or hard disk Military weapons, guidance and positioning systems.