LC-3

Little Computer 3

LC-3 minimal computer from introduction to computing systems

• 16bit instructions
  • 4bit opcode
  • 12bit operands
• Memory
  • 8 General Purpose Registers of 16bit
  • Address space: 16bit
  • Adressibility: 16bit
  • Load/store architecture: load data first in registers before performing operations.
• ALU
  • Only has ADD, AND and NOT operations, other operations must by implemented by programs

Instruction processing #

• Fetch
  • Load instruction into IR
  • Increase PC to next instruction
• Decode: examinates opcode
• Evaluate address: sign-extend addresses needed
• Fetch operands: obtains source operands
• Execute: executes the instruction performed in ALU
• Store result: store result into memory