Classic Computer Magazine Archive COMPUTE! ISSUE 60 / MAY 1985 / PAGE 10

Analog Vs. Directional Joysticks

I was recently dismayed to find that I cannot connect the Wico controllers from our Atari 2600 to our IBM PCjr. The local computer store advised that I need analog controllers. I am confused. What is the difference between controllers, other than planned obsolescence?

David A. Baxter

It's not planned obsolescence, just two different ways of designing a joystick controller. The joysticks used on the Atari 2600, Atari home computers, Commodore home computers, and Coleco Adam are directional. When the stick is deflected, one or two switches are closed, and the joystick returns a value to the computer which corresponds to one of eight directions (up, down, left, right, and the four diagonals). Computer programs check this value to determine the stick's direction, and then move a marker or player accordingly.

There is another way of designing a joystick which has been used with the IBM PC, PCjr, Apple II series, and TRS-80 Color Computer. These are analog joysticks. When the stick is deflected, they return a value which corresponds not only to the direction, but also to how far the stick was moved. They are more like paddle controllers on Atari and Commodore machines, with one paddle for the horizontal axis, and one for the vertical. (In fact, you could build an analog joystick for an Atari or Commodore by combining two paddle controllers.)

When you move a paddle controller from left to right, it returns a number, say from 0 to 255. That means there are 256 possible horizontal positions. The same type of value is used for the vertical axis. So analog joysticks tell the computer an absolute position—to which spot the joystick is pointing—instead of in which direction the joystick is pointing.

Which joystick is best depends upon the application. For a game requiring simple directional information—such as Pac-Man—directional sticks are superior, be-cause the action is more positive. On the other hand, analog sticks are preferable for games in which you want to rapidly move an object to a new position on the screen without moving across all the intervening positions (for example, the aiming crosshair in Missile Command, although most versions of this game use directional joysticks or trackballs).

Because analog joysticks are a little more complicated to manufacture, they cost more. Another drawback is their thumb-wheels for adjusting the range of values returned. There are usually two thumbwheels somewhere on the joystick, one for adjusting the vertical values and another for the horizontal values. If either thumbwheel is out of adjustment, the joystick can return wild values that the program can't interpret. A perfectly healthy program can crash with an "Illegal function call" or similar error message, and you might never suspect that it's the fault of the joystick. Some programs circumvent this problem by including routines for calibrating the joystick.