Tag Archives: MSX2

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.

Developing For Vintage Hardware

It was a hectic but very productive week here at 16-BIT Shock HQ. Progress on the development of Project MSG continues tenaciously. While I’m not in a position to give a solid release date, it won’t be too far away.

Given the retro leanings of the project, there has been interest by some members of the homebrew community. I’ve been asked if there is a possibility for the game to be ported over to certain vintage systems. While neither myself or my development partner can commit to any additional platforms, right way. After all, Android support is by far the most requested platform for obvious reasons.

I also have a burgeoning interest in HTML5 development lately. Whether Project MSG is suited for this remains unclear – time will tell. 

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Sega’s Mega Drive boasts one of the finest exterior designs for a game console

Nevertheless, developing for vintage hardware is an intriguing prospect that personally find exciting. The Sega Mega Drive / Genesis is the first potential candidate on the list. An amazing 16-bit console that possesses, near ideal specifications for the results that I want. I will need to brush up on my 68000 assembly, perhaps even some Z80 skills will come in handy. Once a proud owner of a Sinclair ZX Spectrum, learned enough Z80 assembly to code a Joust clone. But that was a very long time ago and I’m certainly a bit rusty now.

Speaking of the ZX Spectrum, that would make both a good & bad contender for a Project MSG port. It would be quite possible with tight, efficient coding. However, the little 8-bitter is rather weak in some areas. Particularly in the sound department, especially if we’re referring to the 16K/48K variants of the microcomputer. The Spectrum 128 on the other hand, apart from increased RAM also came equipped with the AY-3-8912, a 3-channel audio chip. Capable of producing superior music and sound effects to it’s forerunner.

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The ZX Spectrum was the true king of the 80’s

In all seriousness though, developing for a 16-bit system such as the Mega Drive or a close counterpart such as the Commodore Amiga, would be ideal. Although they both sport similar processors, they’re entirely different beasts to work on. Specifically in the way the two machines handle graphics, distinctively. The Amiga is well known for it’s graphical prowess and blitter, incredibly advanced for the period. Sega’s Mega Drive on the other hand seems rather anemic in the video display processor (VDP) department. With only 64K of video ram and far smaller colour count to the Amiga, yet breezier in the movement of sprites and 2D planes.

Of course there are several other computers and consoles that could come under consideration. While I’ve never owned one of these, MSX & 2/2+ have fascinated me to some degree. As a huge Compile fan, I loved how Aleste 1 & 2 and Aleste Gaiden turned out on the MSX2. A significantly capable machine that just seems to punch above it’s weight, resulting in output similar to that of Sega’s Master System.

Some food for thought, plenty of great machines of yore to ponder upon. Many of which still retain a huge following to this very day. Hopefully it won’t be long whereby I can lend my support to one or two of these systems.