COA Unit-1 (Part-II).pdf

UNIT – 2 Control Unit Organization - Basic Concept of Instruction, Instruction Types, Micro Instruction Formats, Fetch and Execution cycle, Hardwired control unit, Micro-programmed Control unit - micro program sequencer Control Memory, Sequencing and Execution...

UNIT – 2 Control Unit Organization - Basic Concept of Instruction, Instruction Types, Micro Instruction Formats, Fetch and Execution cycle, Hardwired control unit, Micro-programmed Control unit - micro program sequencer Control Memory, Sequencing and Execution of Micro Instruction. BASIC CONCEPT OF INSTRUCTION The user of a computer can control the process by means of a program. A program is a set of instruction that specify the operations, operands and the sequence by which processing has to occur. A computer instruction is a binary code that specifies a sequence of micro-operations for the computer. Instruction codes together with data are stored in memory. The computer reads each instruction from memory and places it in a control register. The control then interprets the binary code of the instruction and proceeds to execute it by issuing a sequence of micro-operations. INSTRUCTION TYPES & FORMATS A basic computer has three types of instructions: a. Memory reference instructions b. Register reference instructions c. Input-Output instructions Memory Reference Instructions - Below instruction format for memory reference instructions. Each memory reference instruction has 16-bits. Out of 16-bits: l-Bit (I) specifies addressing mode : Direct or indirect 3-Bits (Opcode) specify the opcode and 12-Bits (Address) specify the address. 15 14 12 11 0 I Opcode Address I = 0: Direct addressing mode I = 1: Indirect addressing mode Opcode:It can have value from 000 through 110 since there are 7 memory reference instructions Example: Mnemonic Description Instruction Code in HEX Logi all ANDs the o te ts of Spe ified I=0 I=1 AND memory location and AC AC