This chapter explained the configuration of the parallel port and the digital logic concepts involved when using the port with external circuitry. These concepts include binary notation, digital logic levels, noise margins and different types of logic families such as CMOS and TTL.
The PC parallel port uses three I/O addresses to transfer data through the port’s interface. Each address controls one byte of data, however, for two I/O addresses, several data bits are unused and a few other bits are inverted internally by the port circuitry. The first I/O address is used to output data only, the second address is used to input data through the port and the last address can be used to both input and output data. Furthermore, representation of data using decimal, hexadecimal and binary number systems has been explained. This knowledge will be used when developing programs in the chapters ahead.