Game 7 Unit 1 of 6 1 hr learning time

Place the Rover

Before the rover can move, it has to exist. Hold its position in two variables and draw it with two POKEs — a bright block in screen memory, its colour alongside. The whole game starts from this: the rover is just two numbers and two pokes.

17% of Rover

Before a rover can be driven, it has to be somewhere. And on the C64, "somewhere on screen" is just a row and a column — two numbers. So start by holding the rover's position in two variables and drawing it where they point.

10 POKE 53281,0
20 PRINT CHR$(147)
30 R=12:C=20
40 POKE 1024+R*40+C,160
50 POKE 55296+R*40+C,7
A C64 screen, black background, with a single bright yellow block in the centre.
The rover: one bright block, placed where R and C point. It doesn't move yet — but everything that follows is just changing those two numbers and redrawing.

Two variables hold the rover: R for its row, C for its column, set on line 30 to the middle of the screen. Line 40 draws it — POKE 1024 + R*40 + C, 160 puts a solid block into screen RAM at that row and column, using the 1024 + R*40 + C address you met in the primer and used all through Skyline and Tally. Line 50 sets its colour with the matching 55296 + R*40 + C in colour RAM — yellow (7), bright against the black.

That's the whole idea, and it's worth pausing on: the rover is two numbers and two pokes. To move it, you'll change R or C and draw again. Everything in Rover — the driving, the walls, the collisions — is built on this one foundation: a position you can change, and a block you can redraw wherever it lands.

Try this

  • Move it by hand. Change R and C on line 30 to different values and run again. The rover appears wherever you point it — proof the position is just data.
  • Pick its look. Try colour 1 (white) or 2 (red) on line 50, or a different character code than 160 on line 40. Choose a rover that reads instantly against black.

What's next

The rover sits still because nothing changes R and C. In Unit 2 the joystick changes them on every pass of a loop, and the rover drives wherever you push the stick.