The PC parallel port is composed of 4 control lines, 5 status lines and 8 data lines. The control lines are output lines, the status lines are input lines and the data lines are bi-directional. We used the 3 of the control lines as output lines and the 8 data lines as input/output lines. The direction of the data lines is controlled by a 5th control bit which is internally (does not show on the port). In general, writing to the port is done by writing to a certain location in memory which is reserved for the port. The writing is done in 8 bits (bytes). For more information regarding the PC parallel port see http://www.geocities.com/SiliconValley/Bay/8302/parallel.htm.