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Atari 2600 Programming for Newbies

Session 1: Start Here

By Andrew Davie (adapted by Duane Alan Hahn, a.k.a. Random Terrain)

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Page Table of Contents

Original Session

So, you want to program the Atari 2600 and don't know where to start?

 

Welcome to the first installment of "000001010 00101000 00000000 1100101"which at first glance is a rather odd name for a programming tutorialbut on closer examination is appropriate, as it is closely involved with what it's like to program the Atari 2600. The string of 0's and 1's is actually a binary representation of "2600 101".

 

I'm Andrew Davie, and I've been developing games for various computers and consoles since the late 1970s. Really! What I plan to do with this tutorial is introduce you to the arcane world of programming the '2600, and slowly build up your skill base so that you can start to develop your own games. We'll take this in slow easy stages.

 

Developing for the Atari 2600 is much simpler today than it was when the machine was a force in the marketplace (back in the 1980s). We have a helpful online community of dedicated programmers, readily available documentation, tools, and sample codeand online forums where we can pose questions and get almost instant feedback and answers. So don't be scaredwith a bit of effort, anyone can do this!

 

It is this online community which makes developing for the machine 'fun'though I use that in the broadest sense of the word. My 'fun' may be another man's 'torture'. For programming this machine is tricky at bestand not for the feint of heart. But the rewards are greatmaking this simple hardware do anything at all is quite an achievementand making it do something new and interesting gives one a warm fuzzy feeling inside.

 

So, let's get right into it … here's your first installment of "2600 101". We're going to assume that you know how to program *something*, but not much more than that. We'll walk through binary arithmetic, hexadecimal, machine architecture, assemblers, graphics, and whatever else gets in our way. And we'll probably divert on tangential issues here and there. But hopefully we'll come out of it with a greater understanding of this little machine, and appreciation for the work of those brilliant programmers who have developed the classics for this system.

 

 

 

 

 

The Basics

A game on the '2600 comes in the form of a cartridge (or 'tape') which is plugged into the console itself. This cartridge consists of a circuit board containing a ROM (or EPROM) which is basically just a silicon chip containing a program and graphics for displaying the game on your TV set. This program (and graphics) are really just a lot of numbers stored on the ROM which are interpreted by the CPU (the processor) inside your '2600 just like a program on any other computer. What makes the '2600 special is … nothing. It's a computer, just like any other!

 

A computer typically consists of a CPU, memory, and some input/output (I/O) systems. The '2600 has a CPU (a 6507), memory (RAM for the program's calculations, ROM to hold the program and graphics), and I/O systems (joystick and paddles for input, and output to your TV).

 

 

 

 

The CPU

The CPU of the '2600 is a variant of a processor used in computers such as the Apple II, the Nintendo NES, the Super Nintendo, and Atari home computers (and others). It's used in all these machines because it is cheap to manufacture, it's simple to program, but also effectivethe famous '6502'. In this course we will learn how to program the 6502 microprocessor … but don't panic, we'll take that in easy stages (and besides, it's not as hard as it looks).

 

The '2600 actually uses a 6507 microprocessorbut this is really just a 6502 dressed in sheep's clothing. The 6507 is able to address less memory than the 6502 but is in all other respects the same. I refer to the '2600 CPU as a 6502 purely as a matter of convenience.

 

 

 

 

Memory

Memory is severely restricted on the '2600. When the machine was developed, memory (both ROM and RAM) were very expensive, so we don't have much of either. In fact, there's only 128 BYTES of RAM (and we can't even use all of that!)and typically (depending on the capabilities of the cartridge we're going to be using for our final game) only about 4K of ROM. So, then, here's our first introduction to the 'limitations' of the machine. We may all have great ideas for '2600 games, but we must keep in mind the limited amount of RAM and ROM!

 

[If you'd like to create and sell games with a lot more ROM and RAM, check out the Melody boards at AtariAge. And be sure to pick up a Harmony Cartridge for testing your games on a real Atari 2600.]

 

 

 

 

Input/Output

Input to the '2600 is through interaction by the users with joystick and paddle controllers, and various switches and buttons on the console itself. There are also additional control devices such as keypadsbut we won't delve much into those. Output is invariably through a television picture with sound (the game that we see on our TV).

 

So, there's not really much to it so farwe have a microprocessor running a program from ROM, using RAM, as required, for the storage of dataand the output of our program being displayed on a TV set. What could be simpler?

 

 

 

 

 

The Development Process

Developing a game for the '2600 is an iterative process involving editing source code, assembling the code, and testing the resulting binary (usually with an emulator). Our first step is to gather together the tools necessary to perform these tasks.

 

 

 

 

Source Code

'Source code' is simply one or more text files (created by the programmer and/or tools) containing a list of instructions (and 'encoded' graphics) which make up a game. These data are converted by the assembler into a binary which is the actual data placed on a ROM in a cartridge, and is run by the '2600 itself.

 

 

 

 

Text Editor

To edit your source code, you need a text editorand here the choice is entirely up to you. I use Microsoft Developer Studio myself, as I like its featuresbut any text editor is fine. Packages integrating the development process (edit/assemble/test) into your text editor are available, and this integration makes the process much quicker and easier (for example, Developer-Studio integration allows a double-click on an error line reported by the assembler, and the editor will position you on the very line in the source code causing the error).

 

 

 

 

Assembler

To convert your source code into a binary form, we use an 'assembler'. An assembler is a program which converts assembly language into binary format (and in particular, since the '2600 uses a 6502-variant processor, we need an assembler that knows how to convert 6502 assembly code into binary). Pretty much all '2600 development these days is done using the excellent cross-platformAvailable for multiple machines such as Mac, Linux, Windows, etc. assembler 'DASM' which was written by Matt Dillon in about 1988.

 

DASM is available online. It would be a good idea to go there now and get a copy of DASM, and the associated support-files for '2600 development. In this course, we will be using DASM exclusively. We'll learn how to setup and use DASM shortly. [DASM is also included with batari Basic, so you could get it there if you don't trust other sources.]

 

 

 

 

Emulator

Development of a game in the 1980s consisted of creating a binary imageWrite source code, assemble into binary. and then physically 'burning' the binary onto an EPROM, putting that EPROM onto a cartridge and plugging it into a '2600. This was an inherently slow process (trust me, I did this for NES development!) and it sometimes took 15 minutes just to see a change!

 

Nowadays, we are able to see changes to code almost immediately because of the availability of good emulators. An emulator is a program which pretends to be another machine/program. For example, a '2600 emulator is able to 'run' binary ROM images and display the results just as if you'd actually plugged a cartridge containing a ROM with that binary into an actual '2600 console. Today's '2600 emulators are very good indeed.

 

So, instead of actually burning a ROM, we're just going to pretend we've burned oneand look at the results by running this pretend-ROM on an emulator. And if there's a problem, we go back and edit our source code, assemble it to a binary, and run the binary on the emulator again. That's our iterative development process in action.

 

There are quite a few '2600 emulators available, but two of note are:

Stella

z26

 

Stella is your best choice if you're programming on non-Windows platform. I use Z26 for Windows development, as it is quite fast and appears to be very accurate. Either of these emulators is fine, and it's handy to be able to cross-check results on either.

 

We'll learn how to use these emulators laterbut right now let's continue with the gathering of things we need…

 

Now that we have an editor, an assembler, and an emulatorthe next important things are documentation and sources for information. There are many places on the 'net where you can find information for programming '2600, but perhaps the most important are:

The Stella List

AtariAge

 

 

 

 

 

Documentation

And finally, documentation. A copy of the technical specifications of the '2600 hardware (the Stella Programmer's Guide) is essential…

Stella Programmer's Guide

- HTML Version

- PDF version

 

 

 

 

 

Summary

OK, that's all we need. Here's a summary of what you should have…

 

That's it for this session. Have a read of the Stella Programmer's Guide (don't worry about understanding it yet), and try installing your emulator (and play a few games for 'research' purposes). Next time we will make sure that our development environment is setup correctly, and start to discuss the principles of programming a '2600 game.

 

P.S. I can't promise to complete this 'course'but hopefully what I do write will be interesting and helpful.

 

 

 

Other Assembly Language Tutorials

Be sure to check out the other assembly language tutorials and the general programming pages on this web site.

 

Amazon Stuff

 

 

 

 

Next Session >

 

 

 

 

 

Session Links

Session 1: Start Here

Session 2: Television Display Basics

Sessions 3 & 6: The TIA and the 6502

Session 4: The TIA

Session 5: Memory Architecture

Session 7: The TV and our Kernel

Session 8: Our First Kernel

Session 9: 6502 and DASM - Assembling the Basics

Session 10: Orgasm

Session 11: Colorful Colors

Session 12: Initialization

Session 13: Playfield Basics

Session 14: Playfield Weirdness

Session 15: Playfield Continued

Session 16: Letting the Assembler do the Work

Sessions 17 & 18: Asymmetrical Playfields (Parts 1 & 2)

Session 19: Addressing Modes

Session 20: Asymmetrical Playfields (Part 3)

Session 21: Sprites

Session 22: Sprites, Horizontal Positioning (Part 1)

Session 22: Sprites, Horizontal Positioning (Part 2)

Session 23: Moving Sprites Vertically

Session 24: Some Nice Code

Session 25: Advanced Timeslicing

 

 

 

 

Useful Links

Easy 6502 by Nick Morgan

How to get started writing 6502 assembly language. Includes a JavaScript 6502 assembler and simulator.

 

 

Atari Roots by Mark Andrews (Online Book)

This book was written in English, not computerese. It's written for Atari users, not for professional programmers (though they might find it useful).

 

 

Machine Language For Beginners by Richard Mansfield (Online Book)

This book only assumes a working knowledge of BASIC. It was designed to speak directly to the amateur programmer, the part-time computerist. It should help you make the transition from BASIC to machine language with relative ease.

The Six Instruction Groups

The 6502 Instruction Set broken down into 6 groups.

6502 Instruction Set

Nice, simple instruction set in little boxes (not made out of ticky-tacky).

 

 

The Second Book Of Machine Language by Richard Mansfield (Online Book)

This book shows how to put together a large machine language program. All of the fundamentals were covered in Machine Language for Beginners. What remains is to put the rules to use by constructing a working program, to take the theory into the field and show how machine language is done.

6502 Instruction Set

An easy-to-read page from The Second Book Of Machine Language.

 

 

6502 Instruction Set with Examples

A useful page from Assembly Language Programming for the Atari Computers.

 

 

6502.org

Continually strives to remain the largest and most complete source for 6502-related information in the world.

NMOS 6502 Opcodes

By John Pickens. Updated by Bruce Clark.

 

 

Guide to 6502 Assembly Language Programming by Andrew Jacobs

Below are direct links to the most important pages.

Registers

Goes over each of the internal registers and their use.

Instruction Set

Gives a summary of whole instruction set.

Addressing Modes

Describes each of the 6502 memory addressing modes.

Instruction Reference

Describes the complete instruction set in detail.

 

 

Stella Programmer's Guide

HTMLified version.

 

 

Nick Bensema's Guide to Cycle Counting on the Atari 2600

Cycle counting is an important aspect of Atari 2600 programming. It makes possible the positioning of sprites, the drawing of six-digit scores, non-mirrored playfield graphics and many other cool TIA tricks that keep every game from looking like Combat.

 

 

How to Draw A Playfield by Nick Bensema

Atari 2600 programming is different from any other kind of programming in many ways. Just one of these ways is the flow of the program.

 

 

Cart Sizes and Bankswitching Methods by Kevin Horton

The "bankswitching bible." Also check out the Atari 2600 Fun Facts and Information Guide and this post about bankswitching by SeaGtGruff at AtariAge.

 

 

Atari 2600 Specifications

Atari 2600 programming specs (HTML version).

 

 

Atari 2600 Programming Page (AtariAge)

Links to useful information, tools, source code, and documentation.

 

 

MiniDig

Atari 2600 programming site based on Garon's "The Dig," which is now dead.

 

 

TIA Color Charts and Tools

Includes interactive color charts, an NTSC/PAL color conversion tool, and Atari 2600 color compatibility tools that can help you quickly find colors that go great together.

 

 

The Atari 2600 Music and Sound Page

Adapted information and charts related to Atari 2600 music and sound.

 

 

Game Standards and Procedures

A guide and a check list for finished carts.

 

 

Stella

A multi-platform Atari 2600 VCS emulator. It has a built-in debugger to help you with your works in progress or you can use it to study classic games. Stella finally got Atari 2600 quality sound in December of 2018. Until version 6.0, the game sounds in Stella were mostly OK, but not great. Now it's almost impossible to tell the difference between the sound effects in Stella and a real Atari 2600.

 

 

JAVATARI

A very good emulator that can also be embedded on your own web site so people can play the games you make online. It's much better than JStella.

 

 

batari Basic Commands

If assembly language seems a little too hard, don't worry. You can always try to make Atari 2600 games the faster, easier way with batari Basic.

 

 

Atari 2600 BASIC

If assembly language is too hard for you, try batari Basic. It's a BASIC-like language for creating Atari 2600 games. It's the faster, easier way to make Atari 2600 games.

Try batari Basic

Back to Top

 

 

In Case You Didn't Know

 

Trump's Jab = Bad

Did you know that Trump's rushed experimental rona jab has less than one percent overall benefit? It also has many possible horrible side effects. Some brainwashed rona jab cultists claim that there are no victims of the jab, but person after person will post what the jab did to them, a friend, or a family member on web sites such as Facebook and Twitter and they'll be lucky if they don't get banned soon after. Posting the truth is “misinformation” don't you know. Awakened sheep might turn into lions, so powerful people will do just about anything to keep the sheep from waking up.

 

Check out these videos:

What is causing the mysterious self-assembling non-organic clots?

If You Got the COVID Shot and Aren't Injured, This May Be Why

Full Video of Tennessee House of Representatives Health Subcommittee Hearing Room 2 (The Doctors Start Talking at 33:28)

 

 

H Word and I Word = Good

Take a look at my page called The H Word and Beyond. You might also want to look at my page called Zinc and Quercetin. My sister and I have been taking those two supplements since summer of 2020 in the hopes that they would scare away the flu and other viruses (or at least make them less severe).

 

 

B Vitamins = Good

Some people appear to have a mental illness because they have a vitamin B deficiency. For example, the wife of a guy I used to chat with online had severe mood swings which seemed to be caused by food allergies or intolerances. She would became irrational, obnoxious, throw tantrums, and generally act like she had a mental illness. The horrid behavior stopped after she started taking a vitamin B complex. I've been taking Jarrow B-Right (#ad) for many years. It makes me much easier to live with.

 

 

Soy = Bad

Unfermented soy is bad! “When she stopped eating soy, the mental problems went away.” Fermented soy doesn't bother me, but the various versions of unfermented soy (soy flour, soybean oil, and so on) that are used in all kinds of products these days causes a negative mental health reaction in me that a vitamin B complex can't tame. The sinister encroachment of soy has made the careful reading of ingredients a necessity.

 

 

Wheat = Bad

If you are overweight, have type II diabetes, or are worried about the condition of your heart, check out the videos by Ken D Berry, William Davis, and Ivor Cummins. It seems that most people should avoid wheat, not just those who have a wheat allergy or celiac disease. Check out these books: Undoctored (#ad), Wheat Belly (#ad), and Eat Rich, Live Long (#ad).

 

 

Negative Ions = Good

Negative ions are good for us. You might want to avoid positive ion generators and ozone generators. A plain old air cleaner is better than nothing, but one that produces negative ions makes the air in a room fresher and easier for me to breathe. It also helps to brighten my mood.

 

 

Litterbugs = Bad

Never litter. Toss it in the trash or take it home. Do not throw it on the ground. Also remember that good people clean up after themselves at home, out in public, at a campsite and so on. Leave it better than you found it.

 

 

Climate Change Cash Grab = Bad

Seems like more people than ever finally care about water, land, and air pollution, but the climate change cash grab scam is designed to put more of your money into the bank accounts of greedy politicians. Those power-hungry schemers try to trick us with bad data and lies about overpopulation while pretending to be caring do-gooders. Trying to eliminate pollution is a good thing, but the carbon footprint of the average law-abiding human right now is actually making the planet greener instead of killing it.

 

Watch these two YouTube videos for more information:

CO2 is Greening The Earth

The Climate Agenda

 

 

How to Wake Up Normies

Charlie Robinson had some good advice about waking up normies (see the link to the video below). He said instead of verbally unloading or being nasty or acting like a bully, ask the person a question. Being nice and asking a question will help the person actually think about the subject.

 

Interesting videos:

Charlie Robinson Talks About the Best Way to Wake Up Normies

Georgia Guidestones Explained

The Men Who Own Everything

Disclaimer

View this page and any external web sites at your own risk. I am not responsible for any possible spiritual, emotional, physical, financial or any other damage to you, your friends, family, ancestors, or descendants in the past, present, or future, living or dead, in this dimension or any other.

 

Use any example programs at your own risk. I am not responsible if they blow up your computer or melt your Atari 2600. Use assembly language at your own risk. I am not responsible if assembly language makes you cry or gives you brain damage.

 

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