Addressing Modes

This document is a student workbook focused on teaching the various addressing modes used in the PDP-11 computer system. It is structured as a self-study unit within a larger curriculum introducing the PDP-11 family.

The workbook's learning objectives include understanding:

• The eight basic addressing modes (Register, Register Deferred, Autoincrement, Autodecrement, Autoincrement Deferred, Autodecrement Deferred, Index, and Index Deferred) and how they locate operands using general-purpose registers (GPRs).
• The differences between direct and deferred addressing.
• Four special addressing modes involving the Program Counter (PC): Immediate, Absolute, Relative, and Relative Deferred.
• Assembler syntax and octal codes for all addressing modes.
• Key terminology such as "base," "index," "pointer," "effective address," "offset," and "position-independent code" (PIC).
• The distinction between relative and absolute addressing.

The material explains each addressing mode with key points, visual references, and examples. It describes how instructions are fetched and decoded, and how addressing modes and register fields combine to specify operand locations. The document also introduces the concept of position-independent code, which allows programs to execute correctly regardless of their memory location by using PC-relative addressing.

The workbook includes exercises to practice basic and special PC addressing modes, along with an answer sheet for self-correction. A final self-scoring test is provided to assess comprehension of the study unit's content.