Instruction codes and computer registers

Instruction codes and computer registers

• 1.
  INSTRUCTION CODES ANDCOMPUTER REGISTERS Nikhil Gaba 8125
• 2.
  Instruction code Aninstruction code is a group of bits that instruct the computer to perform a specific operation. Two parts- Operation code-specifies the operation Address-specifies operands, registers or memory word Address Opcode 0 11 12 15
• 3.
  Stored program organizationMemory 4096 X 16 Address Opcode 0 11 12 15 Processor register 0 15 Binary operand Instructions (program) Operands (data)
• 4.
  Direct and Indirectaddress When the second part of an instruction code specifies the actual operand instruction is said to have an immediate operand. When the second part specifies the address of operand it is called direct address. When the second part specifies the address of the memory word in which address of the operand is found is called indirect address .
• 5.
  Address Opcode 011 12 15 I Memory Memory 0 ADD ADD + + AC AC 22 457 operand operand 457 1 300 300 1350 1350 Direct address Indirect address 14
• 6.
  Basic computer registers0 0 0 0 0 0 0 11 11 15 15 15 0 15 7 7 Program counter Address register Instruction register Temporary register Data register Accumulator Input register Output r
• 7.
  Functions DR -Holdsmemory operand AC -Processor register IR -Holds instruction code TR -Holds temporary data AR -Holds address for memory PC -Hold address of next instruction INPR -Holds input character OUTR -Holds output character
• 8.
  Common bus sysytem