This is a four printed page mini-FAQ with the information essential for programming the PC parallel port. Many subjects are not covered in detail. A parallel port links software to the real world. The normal function of the port is to transfer data to a printer through the eight data pins, using the remaining signals as flow control and miscellaneous controls and indications.
Some modern ports are bidirectional.
This table contains up to three 16-bit words. If less than three ports were found, the remaining entries in the table are zero. The addresses are checked in a specific order, and addresses are put into the table as they are found, so the table will never have gaps. The video card's parallel port is normally at 3BCh. This address is checked first by the BIOS, so if a port exists there, it will be LPT1.