Chapter 1 Microprocessor 1.1 Introduction 18.104.22.168.1 Microprocessor is a controlling unit of a micro-computer, fabricated on a small chip capable of performing ALU (Arithmetic Logical Unit) operations and communicating with the other devices connected to it. Microprocessor consists of an ALU, register array, and a control unit. ALU performs arithmetical and logical operations on the data received from the memory or an input device. Register array consists of registers identified by letters like B, C, D, E, H, L and accumulator. The control unit controls the flow of data and instructions within the computer. Figure 1.1: Block Diagram of Microprocessor. 1.2 How does a Microprocessor Work? 22.214.171.124.1 The microprocessor follows a sequence: Fetch, Decode, and then Execute.Initially, the instructions are stored in the memory in a sequential order. The microprocessor fetches those instructions from the memory, then decodes it and executes those instructions till STOP instruction is reached. Later, it sends the result in binary to the output port. Between these processes, the register stores the temporarily data and 1
2 CHAPTER 1. MICROPROCESSOR ALU performs the computing functions. Here is a list of some of the frequently used terms in a microprocessor : 1. Instruction Set : stand. It is the set of instructions that the microprocessor can under- 2. Bandwidth : It is the number of bits processed in a single instruction. 3. Clock Speed : It determines the number of operations per second the processor can perform. It is expressed in megahertz (MHz) or gigahertz (GHz).It is also known as Clock Rate. 4. Word Length : It depends upon the width of internal data bus, registers, ALU, etc. An 8-bit microprocessor can process 8-bit data at a time. The word length ranges from 4 bits to 64 bits depending upon the type of the microcomputer. 5. Data Types : The microprocessor has multiple data type formats like binary, BCD, ASCII, signed and unsigned numbers. 1.3 A microprocessor can be classified into three categories : The microprocessors are categorised into three types such as: • RISC Processors • CISC Processors • Special Processors Figure 1.2: Categories of Microprocessor.
1.3. A MICROPROCESSOR CAN BE CLASSIFIED INTO THREE CATEGORIES : 3 1.3.1 RISC Processors 126.96.36.199.1 RISC stands for Reduced Instruction Set Computer. It is designed to reduce the execution time by simplifying the instruction set of the computer. Using RISC processors, each instruction requires only one clock cycle to execute results in uniform execution time. This reduces the efficiency as there are more lines of code, hence more RAM is needed to store the instructions. The compiler also has to work more to convert high-level language instructions into machine code. Some of the RISC processors are ? • Power PC: 601, 604, 615, 620 • DEC Alpha: 210642, 211066, 21068, 21164 • MIPS: TS (R10000) RISC Processor • PA-RISC: HP 7100LC 188.8.131.52 Architecture of RISC 184.108.40.206.1 RISC microprocessor architecture uses highly-optimized set of instructions. It is used in portable devices like Apple iPod due to its power efficiency. Figure 1.3: RISC Archutecture 220.127.116.11 18.104.22.168.1 Characteristics of RISC The major characteristics of a RISC processor are as follows: • It consists of simple instructions.
4 CHAPTER 1. MICROPROCESSOR • It supports various data-type formats. • It utilizes simple addressing modes and fixed length instructions for pipelining. • It supports register to use in any context. • One cycle execution time. • LOAD and STORE instructions are used to access the memory location. • It consists of larger number of registers. • It consists of less number of transistors. 1.3.2 CISC Processor 22.214.171.124.1 CISC stands for Complex Instruction Set Computer. It is designed to minimize the number of instructions per program, ignoring the number of cycles per instruction. The emphasis is on building complex instructions directly into the hardware. The compiler has to do very little work to translate a high-level language into assembly level language/machine code because the length of the code is relatively short, so very little RAM is required to store the instructions. Some of the CISC Processors are: • IBM 370/168 • VAX 11/780 • Intel 80486 126.96.36.199 Architecture of CISC 188.8.131.52.1 Its architecture is designed to decrease the memory cost because more storage is needed in larger programs resulting in higher memory cost. To resolve this, the number of instructions per program can be reduced by embedding the number of operations in a single instruction. 184.108.40.206 Characteristics of CISC • Variety of addressing modes. • Larger number of instructions.. • Variable length of instruction formats. • Several cycles may be required to execute one instruction. • Instruction-decoding logic is complex. • One instruction is required to support multiple addressing modes 1.3.3 Special Processors 220.127.116.11.1 These are the processors which are designed for some special purposes. Few of the special processors are briefly discussed: