6502 vs. Z80

Attribute	6502	Z80
Architecture	8-bit	8-bit
Registers	3 general purpose registers (A, X, Y)	6 general purpose registers (A, B, C, D, E, H, L)
Addressable Memory	64KB	64KB
Instruction Set	56 instructions	158 instructions
Instruction Size	1 to 3 bytes	1 to 4 bytes
Interrupts	IRQ, NMI, Reset	INT, NMI, Reset
Clock Speed	1-2 MHz	2-4 MHz
Addressing Modes	6 addressing modes	11 addressing modes
Flag Register	6 flags (N, V, B, D, I, Z, C)	8 flags (S, Z, F5, H, F3, PV, N, C)
Stack	256-byte stack	16-bit stack pointer

Introduction

The 6502 and Z80 are two popular microprocessors that played a significant role in the early days of personal computing. Developed in the mid-1970s, both processors were widely used in home computers and gaming consoles of the time. While they share some similarities, they also have distinct attributes that set them apart. In this article, we will explore the key features and characteristics of the 6502 and Z80, highlighting their strengths and weaknesses.

Architecture

The 6502 and Z80 processors have different architectural designs. The 6502 is an 8-bit microprocessor with a simple and elegant design. It has a three-register architecture, consisting of the accumulator (A), the X index register (X), and the Y index register (Y). The 6502 also features a 16-bit program counter (PC) and a stack pointer (SP). On the other hand, the Z80 is an 8-bit microprocessor with a more complex architecture. It has a set of general-purpose registers, including the accumulator (A), the index registers (IX and IY), and the alternate register set (AF', BC', DE', and HL'). The Z80 also includes a 16-bit program counter (PC) and a stack pointer (SP).

Instruction Set

When it comes to the instruction set, both the 6502 and Z80 have their own strengths. The 6502 has a compact and efficient instruction set, with a limited number of addressing modes. It uses a single-byte opcode for most instructions, which allows for more compact code. However, the 6502 lacks some advanced instructions and addressing modes found in other processors. On the other hand, the Z80 has a more extensive instruction set, with a wide range of addressing modes and advanced instructions. This makes the Z80 more versatile and suitable for complex tasks, but it also results in larger code size.

Clock Speed and Performance

When comparing the clock speed and performance of the 6502 and Z80, it is important to consider the context of the time they were developed. The 6502 was designed to be inexpensive and efficient, with a focus on low-cost home computers and gaming consoles. It typically operated at clock speeds ranging from 1 to 3.5 MHz. On the other hand, the Z80 was designed for a wider range of applications, including business computers and industrial systems. It had a higher clock speed, typically ranging from 2 to 4 MHz, allowing for faster processing and better performance in demanding tasks.

Memory Management

Memory management is another area where the 6502 and Z80 differ. The 6502 has a simple memory model, with a 16-bit address bus that can directly access up to 64KB of memory. It uses a separate address space for program code and data, which simplifies memory management but limits the available memory. On the other hand, the Z80 has a more flexible memory model, with a 16-bit address bus that can directly access up to 64KB of memory as well. However, the Z80 also supports memory banking, allowing it to access larger amounts of memory by switching between different banks. This makes the Z80 more suitable for applications that require larger memory capacities.

Peripheral Support

Both the 6502 and Z80 processors offer support for various peripherals, but they differ in terms of their capabilities. The 6502 has a simple I/O system, with limited built-in support for peripherals. It relies on external chips or custom circuitry to interface with peripherals such as keyboards, displays, and disk drives. On the other hand, the Z80 has a more advanced I/O system, with built-in support for a wider range of peripherals. It includes integrated serial and parallel ports, as well as interrupt controllers and timers, making it easier to interface with a variety of devices without the need for additional circuitry.

Development Tools and Ecosystem

When it comes to development tools and ecosystem, both the 6502 and Z80 have their own advantages. The 6502 had a vibrant and active community, with a wide range of software development tools and resources available. It was widely used in popular home computers such as the Apple II and Commodore 64, which contributed to a rich software library. On the other hand, the Z80 also had a strong ecosystem, with a variety of development tools and resources. It was used in popular computers like the Sinclair ZX Spectrum and the MSX series, which led to a diverse range of software and games.

Conclusion

In conclusion, the 6502 and Z80 are both iconic microprocessors that played a significant role in the early days of personal computing. While the 6502 had a simpler architecture and a more compact instruction set, the Z80 offered a more versatile instruction set and better performance. The 6502 excelled in low-cost home computers and gaming consoles, while the Z80 found its place in a wider range of applications. The choice between the two processors ultimately depended on the specific requirements of the system and the preferences of the developers. Regardless of their differences, both the 6502 and Z80 left a lasting impact on the history of computing and continue to be remembered fondly by enthusiasts and retro computing enthusiasts today.