Tag Archives: 8-bit

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.

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Agent Smith Receives The 16-BIT Shock Treatment

Recently a fellow on twitter known as Dodekatheoi (we’re following each other) requested a pixel-art icon from me for his various social media and gaming accounts. In particular he wanted those icons to represent the infamous antagonist of the Matrix trilogy – Agent Smith. He also required that these icons be at screen dimensions of 100 x 100 and later on at 400 x 400. An intriguing prospect to say the least, which I was happy to dive into.

The Matrix movies are fairly stark visually, this works particulalry well in context. Everyone should have an idea of what these movies are about with their rather pessimistic, cyberpunk flavour. Mostly monotone colour hues are used throughout the trilogy, painting a grim alternate reality. Fortunately, pixel-art with it’s reliance on limited colour palettes is a perfect fit for such renditions in low-rez. Capturing the very essence of what Agent Smith is about would be a key goal. I, therefore opted to work directly from a still image from the movie which perfectly depicted this.

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Agent Smith as originally depicted in video form (left) to a pixel art icon (right)

At first glance, it would seem that by merely dithering the image the desired result would be produced. However, this is not the case as dithering such a low-quality image only produces a terrible, uneven pixel texture. Images like these, typically found with a google search and of standard definition video quality are overwrought with screen artifacts. At best, this image would only result in a cheap, dirty digitized look and not that of carefully crafted pixel art.

Nevertheless, the image was not completely useless – after all the depiction of Agent Smith was ideal. I decided to apply a hard contrast and then mask the image, giving me a good trace of the character. The mask was then layered in a new image to work on at a screen resolution of 100 x 100 pixels. After this I proceeded to clean up the image, getting rid of some nasty, rough edges and those odd pixels that were just at the wrong place.

Next came one of the most important steps in putting together a colour palette that would do the image justice. I decided to work in 8-bits per pixel from the get-go and narrowed the palette down to 12 colours. Initially when I started allocating colours and testing them out, I was already up to 20 colours but quickly ascertained that that’s too much. I gradually got rid of the unneccessary colours, keeping only those that worked best with the others within the palette.

I always keep a Wacom Intuos tablet handy for drawing purposes even though I’m proficient with a mouse. For pixel-art I feel the mouse is often the better choice but there are certain aspects that a pen and tablet handle better. In respect, to drawing organic imagery a pen and tablet beats out the mouse more often than not. Ditto for shading purposes, I’ve found there is a greater speed advantage with the Intuos. And in the case of the Agent Smith icon, the tablet came in as an indispensible tool.

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Pixel Edit of Agent Smith from 8-bit right down to 1-bit colour mode

The process from here on was a matter of working on those dots diligently, for a small image size such as this I seldom use more than 3 layers. Once the image looks satisfactory, it’s time for some minor colour balancing. Finally the image is complete and we have ourselves a nice rendition of Agent Smith with only 12 colours. I decided to further reduce the colour down to 8 colours on a secondary image and then down to 1-bit colour depth which comprises of only 2 colours.

Generally the process as a whole is not terribly complex, nor is it the only way to go about doing this. But I believe this one of the more efficient methods for pixel pushers. In my next pixel art article I will reveal some similar work I’ve done on Raiden, the main protagonist from Metal Gear Rising: Revengeance.

Top 10 Articles Of 2014

We’re almost a fortnight into 2015 and I hope it’s been going great for everyone. Here at 16-BIT Shock HQ, things are moving along at a brisk pace. Work on game projects resumed early last week, after a short holiday break.

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Before moving on with fresh content for the new year, let’s take this opportunity for a brief recap of top posts on this blog. Several articles proved to be quite popular with readers and it would be great to showcase them again. Particularly for those who discovered this blog, only recently. The following list features a quick rundown of those posts truly, resonating with folks during 2014, and my personal viewpoint of why that is the case.

Just click on the relative heading and you will be taken directly to the article:

  1. Tools Of The Trade – GameMaker : Studio – Certainly the most read article on this site by a large margin, and quite understandably so. With the explosion of indie game development in recent years, everyone is looking around for the best ways to make games. This article gives a brief overview of one of the most popular game engines in existence today.
  2. Project MSG – Early Development – The game project I’ve been working on and has fortunately excited a few people. It’s a 2D retro-style shooting game with a top-down view perspective set within a cyberpunk universe. Many folks loved the logo and the pixel-art style, and in turn generated some interesting conversation between us. I appreciate all the input I’ve received and will be sharing more about this project in the near future.
  3. Developing For Vintage Hardware – It’s a no-brainer why this post struck a nerve, after all the number of retro gaming and computer aficionados keeps growing. Homebrew development is both intriguing and reinvigorating within the game development scene. Vintage consoles and computer systems, with their limited capabilities offer alternative, frankly more interesting roads for creative expression.
  4. Cybermanga – I’m a huge fan of anime & manga, particularly from the 80’s – 90’s. And it seems so are plenty of people visiting this site, even attracting significant traffic from Japan. The influence of these art forms play a big part in my own creative path and this post gives a brief overview.
  5. This Is For Retro Lovers – On the 2nd of June 2014, I wrote this blog’s very first post. Short, sweet and straight to the point – ultimately setting the general tone for future articles. Surprisingly it attracted a far larger audience than I was expecting, considering it was very early days for the blog.
  6. The 16-BIT Shock Design Philosophy – Probably one of the more important articles I’ve written here. The goal was to convey the direction that my game development projects were to take. Worth a read for recent visitors.
  7. Prototyping And Arcade Presentation – A fairly recent article, managing to gain far more traction than I was expecting. I covered an issue in games that I feel should gain more attention, and that’s the matter of how they are presented. Arcade games in particular are a great example of how this could be done.
  8. Anti-Establishment – Another one of those articles that had a significant impact with readers. Further reiterating key points from the 16-BIT Shock Design Philosophy article. Perhaps a tad more cheeky, but still attracting small trickles of traffic several months after it was published.
  9. Tools Of The Trade – GraphicsGale – At one point, pixel art seemed like it was a dying art form. Fortunately it has been rejuvenated recently with all the interest in retro and indie gaming. One of the better, if not the best pixel art editor is GraphicsGale. A personal favourite of mine which I go into more detail in this post.
  10. FM Synthesis & Video Games: Kick Drums & Toms – Last but not least, is this excellent article by Joe Giliver from Ocular Audio. Joe’s vast knowledge in music composition and FM synthesis is a great help in understanding what is substantially niche subject matter. Lately FM synthesis, is enjoying growing interest which is in line with the resurgence of retro gaming, computing and 80’s synthesizer music.

Plenty of reading there, great way to start the new year I would think. Future articles will tread similar ground for the most part. However, there will be a shift in focus around the periods when I’ll be releasing my game projects. Naturally there will be greater emphasis on these as should be expected.