DODGE: A Game in 6502 Assembly

DODGE

Type

Game

Language

6502 assembly (64tass)

Size

938 bytes · 4 blocks

Type-in

A BASIC loader: 78 lines of DATA with checksums

Controls

Joystick in port 2, or Z and X; fire or SPACE to start; Q to quit

The first program on this site that is not BASIC. DODGE is a tiny game written in 6502 assembly, the language of the C64’s own processor: steer a ship along the bottom of the screen and dodge the rocks that fall faster and faster. It moves smoothly, 50 times a second, and the graphics chip itself tells the program when a rock hits you. All of it fits in 938 bytes.

Recorded in VICE: the rocks fall a row at a time, the ship moves every frame.

CLOCK: A Digital Clock with Big Digits and an Alarm

CLOCK

Type

Utility

Language

Commodore BASIC V2

Length

74 lines · 13 blocks (3,153 bytes)

Keys

Digits, INST/DEL and RETURN to set it; Y/N for the alarm; any key stops the alarm; Q quits

Special keys

None

Tell the C64 what time it is, and it keeps the time on its own, in big digits across the middle of the screen, with a colon that blinks every second. Set an alarm and at the right minute it beeps and flashes until you press a key. The clock itself is one line of BASIC: everything else is about drawing big numbers quickly.

Recorded in VICE: the minute turns, the alarm goes off, and the colon blinks once a second.

Quadratic Equations: Solving ax²+bx+c=0 in BASIC

QUADRATIC EQUATIONS

Type

Maths

Language

Commodore BASIC V2

Length

64 lines · 7 blocks (1,551 bytes)

Keys

Numbers and RETURN; Y for another equation

Special keys

None

Type in three numbers and the C64 solves ax² + bx + c = 0. It writes the equation out the way you would on paper, shows the discriminant, finds two real roots, one double root or two complex ones, and then checks its own answer by putting it back into the equation. If a is zero it is not a quadratic at all, and the program says what it is instead.

x² + x − 1 = 0: two real roots, and the check comes back 0. Running in VICE.

The Bouncing Ball: Animation with POKE

THE BOUNCING BALL

Type

Graphics

Language

Commodore BASIC V2

Length

30 lines · 4 blocks (956 bytes)

Keys

+ faster, - slower, Q quits

Special keys

None

The simplest way to move something on the C64 screen: POKE a ball into screen memory, rub out the old one, and do it again one step further on. This ball bounces off all four edges, changes colour every time it hits one, plays a note on the SID and keeps count. You can speed it up and slow it down while it runs.

Recorded in VICE. Every bounce brings a new colour and a note. Now and then you may catch two balls for an instant: the new one is drawn just before the old one is erased.

Running the Programs: VICE, .PRG Files and Real Hardware

AT A GLANCE

Emulator

VICE, free, for Windows, macOS and Linux

Which C64

x64sc, the cycle-exact one

Run a .PRG

Drag it onto the VICE window

Real C64

Copy the .PRG to an SD card for an SD2IEC, then LOAD"NAME",8

Every listing on this site comes with a ↓ .PRG button: the finished program, ready to load. This page shows how to run those files in VICE, the emulator used to test every listing here, and on a real Commodore 64.

How to Type In a Listing

AT A GLANCE

Letters

Type them without SHIFT

Each line

Line number, then the code, then RETURN

{CODES}

Keys pressed inside quotes; the legend under each listing says which

Save

SAVE"NAME",8 every few minutes

Stuck?

LIST the line from the error and compare it, character by character

In the 1980s, most software for the Commodore 64 arrived on paper. Books and magazines printed programs line by line, and you typed them in. It took an evening, the first RUN usually ended in ?SYNTAX ERROR, and it was the best way ever invented to learn BASIC. This guide covers everything you need to type in the listings on this site, on a real C64 or in an emulator.

ZARIA: Three Dice on the Commodore 64

ZARIA

Type

Game

Language

Commodore BASIC V2

Length

49 lines · 7 blocks (1,615 bytes)

Keys

Any key rolls, Q quits

Special keys

None, everything is typed as CHR$()

Zaria is Greek for dice. Press a key and three dice tumble across the screen, slowing down with a rattle from the SID, until they land and the C64 adds them up. Doubles and triples get called out. It is a short program, but it touches most of what makes the C64 screen fun to work with in BASIC: reverse video, cursor control codes, PETSCII graphics, and a sound chip that is one POKE away.

Two rolls, recorded in VICE. Each one tumbles for about two seconds before the dice settle.