PARALLEL PORT

A 'parallel port' is a type of socket found on personal computers for interfacing with various peripherals. It is also known as a 'printer port' or 'Centronics port'. The IEEE 1284 standard defines the bi-directional version of the port.
For the most part, the USB interface has replaced the Centronics-style parallel port. Some printers use an ethernet connection instead, and — as of 2006 — many lack a parallel port connection. On many modern computers, the parallel port is omitted for cost savings, and is considered to be a legacy port. In laptops, access to a parallel port is still commonly available through docking stations.

Contents

Uses

Port addresses

Program interface

See also

References

Uses

★ Printers

★ Zip drive

★ Some scanners

★ Some sound cards

★ Some Webcams

★ Some gamepads and joysticks

★ Peripheral devices such as EPROM programmers

★ SCSI devices via a Parallel to SCSI adapter

★ Experimental setups using the 12 TTL drivers.

★ External CD-Rom/RW drives

Port addresses

Traditionally IBM PC systems have allocated their first three parallel ports according to the configuration in the table below.

PORT NAME	Interrupt #	Starting I/O	Ending I/O
LPT1	IRQ 7	0x3bc	0x3bf
LPT2	IRQ 5	0x378	0x37f
LPT3	IRQ 5	0x278	0x27f

If there is an unused LPTx slot, the port addresses of the others are moved up. (For example, if a port at 0x3bc does not exist, the port at 0x378 will then become LPT1.) The IRQ lines, however, remain fixed (therefore, 0x378 at LPT1 would use IRQ 7). The port addresses assigned to each LPTx slot can be determined by reading the BIOS Data Area (BDA) at 0000:0408.
Bit to Pin Mapping for the Standard Parallel Port (SPP):

Address		MSB							LSB
	Bit:	7	6	5	4	3	2	1	0
Base	Pin:	9	8	7	6	5	4	3	2
Base+1	Pin:	~11	10	12	13	15
Base+2	Pin:					~17	16	~14	~1

~ indicates a hardware inversion of the bit.

Program interface

In versions of Microsoft Windows that did not use the Windows NT kernel (as well as MS-DOS and some other operating systems), programs could access the parallel port with simple outportb() and inportb() subroutine commands. In operating systems such as Windows NT and Unix (NetBSD, FreeBSD, Solaris, 386BSD, etc), the microprocessor is operated in a different security ring, and accesses to the parallel port is inhibited, unless using the required driver. This improves security and arbitration of device contention.

See also

★ TCP/IP

★ NBF

★ LPR

★ SNMP

References

★ Parallel Port Pinouts Configuration

★ Parallel Port Description and programming

★ Axelson, Jan (2000). ''Parallel Port Complete''. Lakeview Research. ISBN 0-9650819-1-5.