The BIOS determines the address and maps it to the parallel ports at boot time. The PC parallel port. Ground NA NA NA Table One shows what all the pins on the connector are for. A single PC parallel port then gives us 12 output bits and four input bits, under normal circumstances. As our first application, let us consider the control of stepper motors.
Stepper motors provide open-loop, relative motion control.
Open loop means that, when you command the motor to take 42 steps, it provides no direct means of determining that it actually did so. The control is relative, meaning that there is no way to determine the shaft position directly. You can only command the motor to rotate a certain amount clockwise or counter-clockwise from its current position. Each pattern causes the motor to move one step. Smooth motion results from presenting the patterns in the proper order.