CISC AND RISC SYSTEM Based on instruction set, we broadly classify Computer/microprocessor/microcontroller into CISC and RISC. CISC SYSTEM: COMPLEX INSTRUCTION SET COMPUTERS: Generally, there are a large number of instructions, each of which has a different permutation of the same operation(like data access, data transfer etc.) or are capable of multi-step operations or addressing modes within single instructions. Permutation- fundamental change 21-Nov-18 Micro 8051

Continues… This gives the programmer flexibility in writing the program, But it occupies more memory. There was a need to reduce the number of instruction per program. This was achieved by having multiple operations within single instruction. Multiple operations lead to many different kinds of instructions. 21-Nov-18 Micro 8051

Continues… Access to memory in turn makes the instruction length variable and fetch decode execute time unpredictable. Making it more complex, thus hardware was made to understand the complexity of instruction set.(Complexity is in Micro program) Intel 8051 is an example of CISC architecture. Other examples are 8085,8086,MC 6800, Z-80 21-Nov-18 Micro 8051

CHARACTERISTICS OF CISC SYSTEM: Large number of instructions: around 100-250 instructions. A large number of addressing modes, variable length instruction formats Execution time for an instruction may take several clock cycles so instruction timing is also different. Efficient use of memory. No or less pipelining. Complexity is in Micro program. 21-Nov-18 Micro 8051

RISC SYSTEM In applications which require more of input , output related operations having few simple instructions that are of the same length allows memory access only with explicit load and store instructions. Hence each instruction performs less work but instruction execution time among different instructions is consistent. This would lead to instruction execution by hardware including multiple number of registers inside CPU. The computer using such instructions is called Reduced Instruction Set Computer (RISC). PIC microcontroller manufactured by Microchip Company is an example for RISC architecture. Explicit- Stated Clearly or Precisely 21-Nov-18 Micro 8051

CHARACTERISTICS OF RISC SYSTEM: Relatively few instructions, instruction are fixed length. Instructions are executed in small clock periods, hence they are faster than CISC. Very few addressing modes. Limited memory access made available to certain instruction. Highly Pipelining. 21-Nov-18 Micro 8051

COMPARISON CISC RISC Complex instructions taking multiple cycles. Simple instructions taking one cycle Most of the instructions refer memory. Very few instructions refer memory Instructions are executed by micro program Instructions are executed by hardware No or Less Pipelined Highly pipelined Variable format instructions Fixed format instructions Single Register Set Multiple Register Set Examples 8085,8086, Pentium (Intel),M6800 (Motorola),Z-80 (Zilog),and microcontroller (8051 series intel) PIC microcontroller from microchip, ARM, Power PC. 21-Nov-18 Micro 8051

Difference between Harvard and Von- Neumann 21-Nov-18 Micro -PIC

Von-Neumann/Princeton architecture It uses a single memory space for both instructions and data. It is also called a stored-program computer. It has limited data transfer rate. This seriously limits the effectively processing speed when the CPU is required to perform minimal processing on large amount of data. Most processor like 8085,8086,M6800, use this architecture

Harvard Architecture Physical separate storage and signal pathways for instructions and data. The CPU can both read an instruction and perform a data access at the same time. A Harvard architecture computer can thus be faster for a given circuit complexity because instruction fetches and data access do not use a single memory.

Continues… Harvard architecture are also frequently used in specialized DSPs,Commonly used in audio or video processing products. Most general purpose small microcontrollers used in many electronics applications, such as PIC microcontrollers by MICROCHIP TECHNOLOGY,INC and AVR BY ATMEL CORP. These processors are characterized by having small amount of program and data memory, and take the advantage of the HARVARD ARCHITECHTURE.

HARVARD ARCHITECTURE (PIC 16c6x/7x ) 21-Nov-18 Micro -PIC

COMPARISON B/W HARVARD AND VON-NEUMANN ARCHITECTURE HARVARD ARCHITECTURE VON-NEUMANN/PRINCETON ARCHITECTURE This architecture consists of separate program and code memory. It consists of common program and code memory. Execution of instructions are faster, because fetching of code and data are separate. Execution of instructions is relatively slow ,because not possible to fetch code and data simultaneously. Execution of instruction takes less instruction (machine) cycle. Execution of instruction takes more instruction (machine) cycle. Use RISC processor Use CISC processor This is greater amount of parallelism This is no need to have parallelism Chip design is complex because of separate memory. The largest advantages is that it simplifies the chip design because only one memory is accessed. Eg: General microcontrollers (PIC), Special DSPs. E.g. Motorola -68HC11 microcontroller,8085,8086, MC6800.

COMPUTER SOFTWARE A set of sequential instructions is written to perform any task by a computer , it is called Computer program. The different types of languages are developed, in order to communicate with computers is called Programming languages or computer languages. Machine language Assembly language High level language

Types of programming languages Machine language: The computer can understand only machine language which uses 0s and 1s. All instructions,memory,number,characters in strings of 0s and 1s. Opcode: Tells which operations to be performed Operand:Tells operation to be performed on which data. OPCODE OPERAND

Continues… Assembly language: It uses symbolic instruction and executable machine codes. Assembler: Assembly language instruction to machine language instruction. General format: [Label:] mnemonic [Operands] [; comment] Eg: START:MOV A,B ; MOVE B TO A

Continues… High level language: This language consists of set of instructions like words and symbol. The specified rules are to be followed while writing programs. INTERPRETERS OR COMPILERS: High level language to machine level language.