68000

Overview

The 68000 architecture, also known as the Motorola 68k, is a 16/32-bit microprocessor architecture developed by Motorola in 1979. It was widely used in personal computers, workstations, and embedded systems due to its powerful instruction set and ease of use.

History of 68000 Architecture

Motorola 68000 (1979): The original 16/32-bit processor that started the 68000 architecture.
Motorola 68010 (1982): An enhanced version of the 68000 with virtual memory support.
Motorola 68020 (1984): Introduced full 32-bit data and address buses, and additional instructions.
Motorola 68030 (1987): Included an integrated MMU (Memory Management Unit).
Motorola 68040 (1990): Added an integrated FPU (Floating Point Unit) and improved performance.
Motorola 68060 (1994): The final and most powerful processor in the 68000 series.

Key Concepts

16/32-bit Architecture: The 68000 architecture is based on a 16-bit data bus and a 32-bit address bus, allowing it to process 16 bits of data at a time and address up to 4 GB of memory.
Registers: The 68000 has a large set of registers for operations.
Addressing Modes: The 68000 supports various addressing modes for accessing memory.
Rich Instruction Set: The 68000 has a powerful and versatile instruction set, making it suitable for a wide range of applications.

68000 Architecture

Registers

Data Registers (D0-D7): Used for general-purpose data operations.
Address Registers (A0-A7): Used for addressing and pointer operations.
Program Counter (PC): Points to the next instruction to be executed.
Status Register (SR): Holds the processor status flags.
Stack Pointer (A7): Points to the current position in the stack.

Example: Simple Assembly Program

    ORG $1000
    MOVE.B #$00, D0    ; Load D0 with 0
loop:
    ADDI.B #1, D0      ; Add 1 to D0
    MOVE.B D0, $2000   ; Store D0 at address $2000
    CMP.B #$10, D0     ; Compare D0 with 16
    BNE loop           ; Branch to loop if D0 is not equal to 16
    STOP #$2000        ; Stop the processor (end of program)

Differences Between 68000 and Other Architectures

16/32-bit vs. 8/16/32/64-bit: The 68000 is a 16/32-bit architecture, while modern architectures like x86 and ARM are 16, 32, or 64-bit.
Rich Instruction Set: The 68000 has a more powerful and versatile instruction set compared to simpler architectures like the 6500 or 68xx.
Large Number of Registers: The 68000 has more registers compared to earlier 8-bit architectures, allowing for more efficient data processing.

Understanding the 68000 architecture is crucial for low-level programming, performance optimization, and system development in environments where 68000 processors are used.

Last modified: 14 December 2024