THE PARALLEL PORT IEEE 1284
Parallel Port

PARALLEL PORT STANDARD IEEE 1284

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IEEE 1284 is a standard that defines bi-directional parallel communications between computers and other devices. In the 1970s, Centronics developed the now familiar printer parallel interface that soon became a de facto standard. The standard became non-standard as enhanced versions of the interface were developed, such as the HP Bitronics implementation released in 1992. In 1991 the Network Printing Alliance was formed to develop a new standard. In March of 1994, the IEEE 1284 specification was released.

The IEEE 1284 standard allows for faster throughput and bidirectional data flow with a theoretical maximum throughput of 4 megabits per second, with actual throughput around 2 megabits, depending on hardware. In the printer venue, this allows for faster printing and back-channel status and management. Since the new standard allowed the peripheral to send large amounts of data back to the host, devices that had previously used SCSI interfaces could be produced at a much lower cost. This included scanners, tape drives, hard disks, computer networks connected directly via parallel interface, network adapters and other devices. No longer was the consumer required to purchase an expensive SCSI card—they could simply use their built-in parallel interface. These low-cost devices provided a platform to leapfrog the faster USB interface into its present popularity, displacing the parallel devices. However, the parallel interface remains highly popular in the printer industry, with displacement by USB only in consumer models.

Specifications

IEEE 1284 can operate in five modes:

Most recent computers that include a parallel port can operate the port in ECP or EPP mode, or both simultaneously.

An IEEE-compliant cable must meet several standards of wiring and quality. Three types of connectors are defined:

IEEE 1284-I device uses IEEE 1284-A and IEEE 1284-B connectors, while IEEE 1284-II device uses IEEE 1284-C connectors.

Transfer mode

Distance (metre)
(AB cable)/(CC-cable)

Speed (bits per second)

Compatibility (SPP)

2/10

360,360

Nibble

2/10

3,174,603

Byte

2/10

1,369,863

EPP

2/10

2,000,000

ECP

2/10

2,500,000

In IEEE 1284 Daisy Chain Specification, up to 8 devices can be connected to a single parallel port.

IEEE 1284 standards

 

 

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