6500

Overview

The 6500 architecture, also known as the MOS Technology 6502, is an 8-bit microprocessor architecture developed by MOS Technology in 1975. It was widely used in early home computers, video game consoles, and embedded systems due to its low cost and simplicity.

History of 6500 Architecture

MOS Technology 6502 (1975): The original 8-bit processor that started the 6500 architecture.
WDC 65C02 (1982): An enhanced version of the 6502 with additional instructions and lower power consumption.
WDC 65816 (1984): A 16-bit extension of the 6502, used in systems like the Apple IIGS and the Super Nintendo Entertainment System (SNES).

Key Concepts

8-bit Architecture: The 6500 architecture is based on an 8-bit data bus, meaning it can process 8 bits of data at a time.
Registers: The 6500 has a small set of registers for operations.
Addressing Modes: The 6500 supports various addressing modes for accessing memory.
Simple Instruction Set: The 6500 has a relatively simple and small instruction set, making it easy to learn and use.

6500 Architecture

Registers

Accumulator (A): Used for arithmetic and logic operations.
Index Registers (X, Y): Used for indexing and loop control.
Stack Pointer (SP): Points to the current position in the stack.
Program Counter (PC): Points to the next instruction to be executed.
Status Register (P): Holds the processor status flags.

Example: Simple Assembly Program

    .org $8000
    .db $00, $10, $20, $30, $40, $50, $60, $70, $80, $90, $A0, $B0, $C0, $D0, $E0, $F0

    .org $FFFC
    .dw $8000

    .org $8000
start:
    LDX #$00        ; Load X with 0
loop:
    LDA data, X     ; Load A with data at address (data + X)
    STA $0200, X    ; Store A at address ($0200 + X)
    INX             ; Increment X
    CPX #$10        ; Compare X with 16
    BNE loop        ; Branch to loop if X is not equal to 16
    BRK             ; Break (end of program)

data:
    .db $00, $10, $20, $30, $40, $50, $60, $70, $80, $90, $A0, $B0, $C0, $D0, $E0, $F0

Differences Between 6500 and Other Architectures

8-bit vs. 16/32/64-bit: The 6500 is an 8-bit architecture, while modern architectures like x86 and ARM are 16, 32, or 64-bit.
Simple Instruction Set: The 6500 has a simpler and smaller instruction set compared to more complex architectures like x86.
Limited Registers: The 6500 has fewer registers compared to modern architectures, which have more general-purpose and special-purpose registers.

Understanding the 6500 architecture is crucial for low-level programming, performance optimization, and system development in environments where 6500 processors are used.

Last modified: 14 December 2024