Assembly Language Programming
Lesson 1: Bits!
By Robert M (adapted by Duane Alan Hahn, a.k.a. Random Terrain)
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Page Table of Contents
Original Lesson
This course assumes no prior knowledge of computer programming. While the examples given in the course are targeted at the 650X family of processors, the ideas presented will apply to assembly language programming and often programming in general.
Please feel free to posts comments or questions into the Lesson threads. If you wish to ask a private question don't hesitate to send me a PM.
The assembler we will be using for this course is DASM. We won't need the assembler for the first several sessions, I will provide links for downloading and installing DASM. DASM is available for DOS, Windows (in a DOS window), Amiga, and Macintosh (OS-9 or OS-X). So the development tools will be available on many platforms.
The Most Important Thing You Need to Know about Computers
Imagine you have a black box with a single light bulb sticking out of it. Sometimes the light is on, sometimes it is off. Please answer these questions:
- What does it mean when the light is on?
- What does it mean when the light is off?
Until you can answer these questions, programming computers will never quite make sense. Everything else we do in this course will be built on this radical idea. Please take a moment to consider these questions. There are no wrong answers, its just a mental exercise to broaden your mind.
The key points that you need to take away from this exercise are:
- The light is either on or off, there are only 2 possible conditions for the light. The light represents a single digital bit.
- The two states of the bit can represent ANY TWO OPPOSING conditions:
1 or 0
YES or NO
"The Player is alive" or "The player is Dead"
"The Fire button is pressed" or "The fire button is not pressed" - All information in a digital computer at its lowest level is composed of bits. There is no piece of information smaller than a single bit.
So how does this relate back to the questions I asked above?
- What does it mean when the light is on?
It means what ever you the programmer want it to mean is true. - What does it mean when the light is off?
The opposing condition for the meaning you give to the bit is true.
By common convention. the values 1 and 0 are used to represent the states of bits. One usually means on, yes, or true. Zero usually means off, no, or false. Notice that I said "by convention" and "usually". You could just as well use "A" and "B" or "Zip" and "Zap", but this makes it hard to talk with others about bits, so we will use 1 and 0 in this class.
This is the great secret of all computers and computer programming in general. When you program in assembly language, you have complete control/responsibility 
to provide the meaning of the values of the bits that make up your program. If you want a bit to mean "The Dragon is awake" when it is 1 and "The dragon is asleep" when it is zero, that is fine. Just understand that the meaning you give to the bit is completely your own invention and when the user pulls out cartridge with your program and puts another one in, that program will apply a completely different meaning to the EXACT SAME BIT.
Other Assembly Language Tutorials
Be sure to check out the other assembly language tutorials and the general programming pages on this web site.
Amazon: Atari 2600 Programming (#ad)
Amazon: 6502 Assembly Language Programming (#ad)
Atari 2600 Programming for Newbies (#ad)
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Lesson 1: Bits!
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 6502 Instruction Set broken down into 6 groups.
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.
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.
Continually strives to remain the largest and most complete source for 6502-related information in the world.
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.
Goes over each of the internal registers and their use.
Gives a summary of whole instruction set.
Describes each of the 6502 memory addressing modes.
Describes the complete instruction set in detail.
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 programming specs (HTML version).
Atari 2600 Programming Page (AtariAge)
Links to useful information, tools, source code, and documentation.
Atari 2600 programming site based on Garon's "The Dig," which is now dead.
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.
A guide and a check list for finished carts.
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.
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.
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.
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Check out these videos:
If You Got the COVID Shot and Aren't Injured, This May Be Why
Thought Experiment: What Happens After the Jab?
The Truth About Polio and Vaccines
What Is Causing the Mysterious Self-Assembling Non-Organic Clots and Sudden Deaths?
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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.
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.
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Watch these two videos for more information:
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
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.