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The Z80 Microprocessor - Pioneering Gaming and Beyond

Edit on Github | Updated: 28th October 2023

The Z80 Microprocessor: Pioneering Gaming and Beyond

The history of the Z80 microprocessor is a tale of innovation and influence that left an indelible mark on the world of computing and gaming. Developed by Zilog in the late 1970s, the Z80 was a significant step forward in the world of microprocessors. It not only powered countless personal computers but also played a crucial role in the early days of the video game industry.

Birth of the Z80

The Z80 microprocessor was created by Federico Faggin, who previously worked on the Intel 4004 and 8080 microprocessors. Released in July 1976, the Z80 improved upon its predecessors and quickly gained popularity due to its enhanced performance and greater functionality.

One of its notable features was its compatibility with the Intel 8080, making it easier for software developers to transition to the Z80 while taking advantage of its superior capabilities. This compatibility played a significant role in the Z80’s success.

A Pioneering Microprocessor

The Z80 was groundbreaking in several ways. It featured a 16-bit architecture, which allowed for more extensive memory addressing and complex operations. This made it particularly appealing for emerging markets like personal computing, where more capable processors were desperately needed.

Moreover, the Z80 was more power-efficient, requiring fewer components for its operation. It found its way into numerous applications beyond personal computers, including embedded systems, calculators, and, of course, early video game consoles.

Z80 in the Games Industry

The Z80 became a cornerstone of the early video game industry. Its performance and versatility made it a natural choice for powering arcade machines and early home gaming consoles. Some iconic games and consoles that relied on the Z80 include:

  • Arcade Machines: The Z80 was a favorite in the arcade gaming industry, powering classics like Pac-Man, Galaga, and Donkey Kong. Its ability to handle real-time, fast-paced gameplay made it invaluable in this domain.
  • ColecoVision: The ColecoVision, an early home video game console, employed the Z80 as its CPU. It allowed players to enjoy a range of arcade-quality games from the comfort of their living rooms.
  • SEGA Master System: The SEGA Master System, a popular competitor to the Nintendo Entertainment System (NES), featured a Z80 as its secondary processor. This architecture enabled it to deliver impressive graphics and sound for its time.
  • ZX Spectrum: The Z80 was not limited to gaming consoles; it also found its way into home computers like the ZX Spectrum. This platform provided aspiring developers with the tools they needed to create their games.


The Z80 microprocessor architecture was designed as a little-endian system for simplicity and compatibility with its predecessors. The Z80 was developed in the late 1970s as an evolution of the Intel 8080, which was also a little-endian architecture. Maintaining little-endian compatibility allowed for easier software migration and reuse of existing code and data formats.

In little-endian systems, the memory addresses increase from the least significant byte (LSB) to the most significant byte (MSB), which can be more straightforward for certain types of memory operations and data handling. This design choice made sense within the context of the Z80’s historical development and the technology of its time.

Expanding a little-endian value involves appending a byte at the end, while in the case of big endian, you need to shift all the bytes one position to the right and place the new byte at the beginning. This property greatly simplifies the development of multiple-precision math routines. The same principle applies to reducing the size of such values.

Legacy and Impact

The Z80 microprocessor’s legacy extends beyond its role in the games industry. It contributed to the growth of personal computing, embedded systems, and various other technological advancements. Its simplicity and efficiency made it an attractive option for developers across multiple domains.

Even today, the Z80 remains a popular choice for hobbyist programmers and retro enthusiasts who appreciate its straightforward architecture and historical significance. It’s a testament to the enduring impact of a microprocessor that played a pivotal role in the early days of gaming and computing.

Sharp LR35902 (The Game Boy CPU)

The Sharp LR35902, which was used in the original Game Boy, is indeed highly similar to the Z80 processor. The LR35902 is often described as a modified or custom version of the Z80, and it shares many of the same core instructions and architecture.

How similar was the Zilog Z80 to the Gameboy’s Sharp LR35902?

Here are some key similarities between the Z80 and the Sharp LR35902:

  • Instruction Set: Both processors feature a similar instruction set, which includes many common assembly language instructions. Programmers familiar with the Z80 found it relatively easy to work with the Sharp LR35902.
  • Clock Speed: The Sharp LR35902 in the Game Boy operated at a clock speed of around 4.19 MHz, which is in the same range as some Z80 variants.
  • Registers: Both processors have a similar set of registers, including general-purpose registers and special-purpose registers like the program counter (PC) and stack pointer (SP).
  • Memory Addressing: The memory addressing modes and memory management were also quite comparable between the two processors.

What were the differences between the Z80 and Sharp LR35902?

However, there were also some differences and limitations in the Sharp LR35902 compared to a standard Z80:

  • Missing Z80 Instructions: Some of the less frequently used Z80 instructions were not present in the Sharp LR35902.
  • No IX and IY Registers: The Sharp LR35902 lacked the IX and IY registers found in some Z80 variants, which could be useful for certain programming tasks.
  • Limited Direct Memory Access: The Game Boy’s memory-mapped I/O and the way it accessed memory were different from the typical Z80 configuration, reflecting the specific requirements of the handheld gaming console.

In summary, while the Sharp LR35902 in the Game Boy was not an exact copy of the Z80, it was highly similar and compatible in many respects. Programmers with experience in Z80 assembly language found it relatively straightforward to work with the Sharp LR35902, allowing them to develop games and software for the Game Boy.

Z80 Game Development

Cross Assembler

In order for game developers to create games on one CPU architecture (e.g 6502 microprocessor) for another architecture such as the Z80 a cross assembler was used.

The cross assembler was capable of translating the human-readable assembly code into a binary format suitable for the Z80, all while ensuring proper memory and processor constraints were met. Once the code was assembled, it could be loaded onto the target Z80-based hardware, such as early home computers and gaming consoles.