Several keys points to making a game on the Commodore 64 are necessary to understand as you begin your journey. I have listed many of these in a bulleted list below.

Banking Memory
Raster Interrupt / Timers
Map / Tiles
Scrolling / Single Screens
C64 Graphics, Sprites, and Memory
Commodore 64 Bank Memory
Characters and Sprite Multicolors
Animation of Sprites
Sprite Collision Detection
Game Plot / Story
Weapons / Tools
Replay value

Commodore 64 Memory

Setting up a game on the Commodore 64 is best done using Assembly language. Now while it is possible to create a simple game in Basic, you are often limited in speed, memory, and graphics. So using the computer’s native Assembly language will steer your ship in the right direction.

Be aware though, that learning Assembly language is not for the faint of heart. It is a solid skill to master, but it is not impossible. Although this is not a complete guide to Assembly language for the Commodore 64, be sure to check out the Machine Language Project and Machine Language tutorial on this site to learn more.

Commodore 64 Rasters and Timers

Raster interrupts allow game routines to run in the background without affecting assembly language code that is running. For example you have a main subroutine and want to have a separate routine for scrolling to exist in another area of memory that won’t slow down the game.

By using a raster interrupt you can tell the computer to occur every 1/60 of a second.

Many popular, commercial games utilize a raster interrupt to manage game characters, screen shifting, and other things to allow the game to run more smoothly. Scrolling the screen is managed much better by using an interrupt routine. This is because the screen is updated every 60 seconds and when you scroll it, the timer clock is being affected causing the screen to appear jerky.

Commodore 64 Map and Tiles

The majority of Commodore 64 games include a map or a maze environment that a player can walk around in. The best games include a nicely detailed map that includes locked doors, hidden passages, traps, sleeping dragons, and many other things to keep the adventures alive.

A map can be created on scratch paper or even graph paper. Just remember that each area that is filled for a regular screen character exists as 8 x 8 with a total of 64 pixels that can be utilized. Keep in mind, also that there are wonderful tools to create maps, such as CharPad, so that you do not have to resort to old school game design.

Scrolling a Commodore 64 Game Map

Having the ability in your game to allow for scrolling the screen can make a game very enjoyable to your player. Although single screen games also have their share of enjoyment, I cannot even count the many, amazing games I have played that involved the screen being shifted to the left, right, or up and down position while moving my game character through a larger world.

Shifting a game screen requires a specific technique that involves capturing data from a game file, and even reading pointer addresses within your code. When the player is walking to edge of the screen, the data in that area must be then copied to the next blocks from the game map so that each new line of pixels come alive on the screen. To learn more about this, be sure to check out my guide on Commodore 64 Screen Scrolling.

A single screen does not require any special scrolling ability. Keep in mind that a screen can be created in single characters (8 x 8) tiles or double wide (4 x 4) tiles. With double wide, 4 tiles are placed side by side in a rectangular shape to produce a more defined tile.  With 8 x  8 tiles, however the graphics are all created inside an individual character (such as is seen on the default Commodore 64/VIC screen) at power up.

C64 Graphics, Sprites, and Memory

Graphics – the character generator ROM is unavailable and must be copied from ROM memory to RAM. So you cannot direct overwrite any of the characters you see on screen to create your own until the character data is copied over where it can be replaced. Visit the page Character ROM Graphics to learn more.

Sprites – these are blocks that are defined into game characters that move over the background without affecting the foreground data there. Yet in Bank 0, they are also limited and must be relocated to allow more sprites to be available in memory.

Game code routines – the rest of the memory exists in a small 8K block that will eventually overwrite data once the limit is reached.

When a cartridge is plugged into the console port, memory is occupied from $8000 through $9000. The Basic ROM is contained in $A000 through $B000. The character ROM set is contained in bytes $C000 through $D000. Finally the Kernal ROM exists in $E000 through $F0000.

According to the book Mapping the Commodore 64, the cassette I/O Buffer contains memory from $33C – $3FB (828-1019). So if the cassette recorder is not in use, this memory is available to be used by Basic and can be beneficial when you want to know How to create a Commodore 64 game. Keep in mind though that only short assembly language routines can be placed here. Often in many Basic programming examples, Basic sprites are relocated to exist here instead.

Commodore 64 Bank Memory

00 (bit value of 0) Bank 3 | 49152-65535, $C000 – $FFFF

01 (bit value of 1) Bank 2  | 32768 – 49151, $8000 – $BFFF

10 (bit value of 2) Bank 1 | 16384 – 32767, $4000 – $7FFF

11 (bit value of 3) Bank 0 | 0 – 16383, $0000 – $3FFF

Basic programming text is actually stored in memory locations $0800  – $9FFF (2048-40959)

The character ROM images reside in memory locations $1000 – $1FFF (4096-8191)

Character and Sprite Multicolors

Sprites can be set to multiple colors (known as multicolor). This allows more colorful characters to be created.

Sprite multicolor registers exist at 53281 – $D021 (background color 0), 53282 – $D022 (background color 1), 53283 – $D023 (background color 2), and 53284 – $D024 (background color 3).

Register 53285 – $D025 (sprite multicolor register 0) manages bit pair 01 and 53286 (sprite multicolor register 1) manages the bit pairs 11.

Animation of sprites

One of the fun things about working with Commodore 64 sprites, is having the ability to create animation movement for them. Many games demonstrate a sprite that can walk, run, jump, duck, kick, fight, and so on. This is all possible due to the ability to shift frames in motion. The frames are contained in memory locations $7FB-$7FF (2040-2047) that exist for 8 sprites (0-7). Each sprite is 24 bits in width and 21 lines in height. Be sure to check out my article called C64 Sprites Defined.

Sprite Collision Detection

Having very good sprite collision detection is necessary to prevent frustrating game play. All too often in my childhood I spent many tiring nights trying to win a game only to learn more years later that the developers had constructed very poor collision detection and nearly made those games impossible to beat.

One of the better devised methods of making this possible, is programming a game so that a sprite can detect when it has pushed up against any wall or encountered an enemy in the same area of space. This is accomplished by allowing a sprite to contact delta checkpoints (up, down, left, and right) that determine when a sprite’s pixels have overlapped with another background character’s information. Also sometimes deltas may have to be adjusted depending on how the map is scrolling.

Now since the sprite has more pixels than a character background, a special algorithm is needed to match up a sprite’s pixels with a background character’s pixels reduced to an 8 x 8 image area with a total of 64 pixels.

Plot for Commodore 64 Game Design

Having a “plot” for a Commodore 64 game is necessary when you are creating some type of adventure game. Other games like shoot em ups can get away with no story line, but the best games utilize them effectively.

I can imagine that the best way to approach this is breaking down characters in a game, having a mission for each, creating boss battles at the end of levels, and eventually reaching your destination in winning the game.

So I like to have a main protagonist that receives the largest spotlight throughout the game. This player could be sent on a mission by a king as an example to recover lost jewels, a kidnapped princess, or some other type of folklore that draws interest to the people playing your game. I could go into more detail, but just keep this in mind when building a larger game that can go on for a while.

Game Weapons and Tools

Nearly every game must include some type of weapon to keep it interesting. So when learning How to make a Commodore 64 game, it is suggested to create an inventory list for your game player and the enemies that exist. To make it even more addictive, you could allow a player to utilize weapons that have unique abilities. For example, a golden sword that has the power to kill a dragon.

Another good prospect would be to include tools that can be used by your main player. So for example, imagine a character that finds a shovel and can now use that to search for buried treasure in a dark cave, or even a flashlight to illuminate the cave so the player can see hidden paths that may exist.

Just remember, your imagination is endless and have fun with it.

Commodore 64 Replay Game Value

If you have played a lot of Commodore 64 games, then you will have discovered what makes a good game that you will play it again. Shoot up up action games are popular in that a player will often attempt to beat their last highest score. Adventure games have replay value since a player will need to work up a specific set of skills to proceed further through the game worlds.

So spend time thinking about How to make a Commodore 64 game when you want to make it very fun, addictive and invite people to play it over and over. Having a good strategy in the game should allow the player to restart after they have been killed or completed a level.

I hope you enjoyed this article on Commodore 64 game design and I look forward to playing any future games you create. Thanks for reading.

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