anthony morris
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Pep/9

Pep/9 CPU and memory

Instruction Format

Pep/9 instruction format

  • Either 1 byte or 3 bytes in length
    • 1 byte --> operand specifier not included
    • 3 bytes --> operand specifier included
  • Two parts
    • 8-bit instruction specifier
    • 16-bit operand specifier

Instruction Specifier

  • Op codes vary from 4 bits to 8 bits long
  • 5th bit is the register specifier
  • 3-bit addressing mode specifier
    • Indicates hot to interpret contents of operand specifier
    • Address mode 000000 --> operand specifier contains data value to be used as operand
      • Immediate
    • Address mode 001001 --> operand specifier contains memory address
      • Direct

Computer Science Computing Systems

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