Tag Archives: MSX 2

In Praise Of Zilog’s Z80 Microprocessor

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The choice of the 8-bit generation!

Video games are an electronic medium and quite naturally require some form of computer hardware to run on. The CPU (central processing unit or processor if you prefer) has always played a vital part in the creation and execution of game code. Without this important component, video games would simply not exist. After all the processor is essentially the brain of a computer system…basic stuff!

And just as human brains can vary in intellectual capacity, various makes and models of microprocessors offer different performance capabilities. For game related tasks, the GPU (graphics processing unit) plays an even greater role within the modern game development paradigm. However, this article is not about development techniques and how they are to be applied to modern hardware. Rather, we will look at a specific microprocessor which played a leading role in defining gaming during it’s early stages.

Two prominent periods of gaming are the 8-bit and 16-bit eras, and quite frankly of greatest import. As shiny as our games are, and powerful as our hardware is nowadays – none of this would exist without the groundwork laid down during those halcyon days. And both those eras brought forward to amazing microprocessors that truly revolutionized gaming, namely the Zilog Z80 and the Motorola 68000.

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The Z80 is one of the most important microprocessors in gaming history

Zilog’s Z80 truly helped to kick start affordable home computing and arcade gaming from the late 70’s onward. The Z80 is an 8-bit processor, which is closely based on Intel’s earlier 8080 CPU. Due to it’s performance and versatility, it was adopted by a large variety of computer and arcade amusement vendors. Either Zilog’s original CPU, clones or variants of the Z80 architecture was incorporated into motherboards worldwide. Everyone from Sinclair Research right through to Sega made use of this mighty little chip, benefiting gaming inexplicably.

Some will argue in favour of a rival 8-bit microprocessor, namely the 6502 by MOS Technology. Also very popular and widely used, particularly in the home computer market but also made in-roads in the arcades thanks to Atari. However, the true acid test of which 8-bit processor was better, rests with the greater adoption enjoyed by the Z80, especially among Japanese arcade manufacturers. From Namco’s Galaxian through to Irem’s M52 system boards, the Z80 was the CPU of choice.

None can downplay the wide adoption of the Z80 when considering it brain-powered the following systems:

  • Sinclair ZX80 & ZX81
  • Sinclair ZX Spectrum 16K / 48K / + / 128K / +2 / +3
  • Amstrad / Schneider CPC464 / 464plus / CPC664 / CPC6128 / 6128plus
  • Amstrad GX4000
  • Cambridge Z88
  • SAM Coupé
  • Tandy / Radio Shack TRS-80 series
  • Coleco’s – ColecoVision
  • Commodore 128 (includes both a Zilog Z80A & MOS 8602)
  • NEC PC-6001 / mkII / mkIISR (using NEC’s μPD780C – a Z80 compatible CPU)
  • NEC PC-6601
  • NEC PC-8000 series
  • NEC PC-8801 (a wide range of models manufactured between 1981 – 1989)
  • MSX 2 / 2+ / turboR
  • Sharp MZ-80K series / MZ-80B series / MZ-3500 series
  • Sharp X1 / X1 turbo / X1 turbo Z / X1 twin 
  • Sony SMC-70
  • Sega SG-1000 / SG-1000 II / SC-3000 / Mark III / Master System
  • Sega Game Gear
  • Sega Mega Drive / Genesis (includes both a Motorola 68000 & Zilog Z80)
  • SNK Neo Geo (includes both a Motorola 68000 & Zilog Z80)
  • SNK Neo Geo Pocket / Color (includes both a TOSHIBA TLCS-900H & Z80)
  • Nintendo Game Boy / Color (Sharp LR35902 – a custom Z80 CPU)

The above list is only a small segment of computer and console systems that the trusty Z80 found itself in. Arcade manufacturers in particular, truly took advantage of this versatile processor in numerous ways. Initially arcade boards would only be designed with a singular Z80 CPU in place. But as games were becoming more complex, some added processing grunt was required. Since the Z80 was affordable and developers already accustomed to coding games for it, a very common solution was to add a secondary Z80 to increase the board’s horsepower.

SNK (Shin Nihon Kikaku Corporation) were always partial to manufacturing some fantastically exotic boards. During the mid-80’s they came up with the SNK Triple Z80 arcade board, and as the name suggests – boasts three Zilog Z80’s working in tandem. Two Z80’s were allocated to handle main CPU duties, while the third was specifically for sound CPU tasks. The games that ran on this board naturally surpassed the audio and visual fidelity of many of it’s counterparts. Resulting in games that had a look, feel and sound closer to the 16-bit standard.

My personal experiences with the Z80 were both positive and enjoyable, owning a ZX Spectrum played a big part in this. I learned to program on it, firstly in BASIC and then later on in machine code – wasn’t easy but I got the nitty-gritty. Later on I got hold of Zeus Assembler which made programming in assembly far more palatable to machine code.

Generally it didn’t take long to get accustomed to how the accumulator and various registers within the Z80 work together. The architecture is simple and elegant enough, not hard to figure out why it was so readily adopted. Not bad for a microprocessor that was originally intended for cash registers, instead of computers, consoles and arcade machines.