Computer Organization, Instruction Set Architecture, Gateforum

Question

Consider a system with 16 Registers(Ro,R1,...R8).An instruction SUB Ro,R1 , which is two bytes long,what is the space assigned to the opcode field (in bits) ?

Comments

ans became 8 bit  opcode becuase 4 bit for 1^st reg  addressing mode   and next 4 bit for 2nd next register addressing mode  so only 8 bit left from 16 bit  instruction format is opcode...registermode….regitsermode

Answer 1

Therefore, we require 8 bits for Opcode. Also, note it is 2 address instruction format.