IEEE 1284
Encyclopedia
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 port
that soon became a de facto
standard. The original standard became non-standard itself 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 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 megabyte
s per second; actual throughput is around 2 megabytes/second, 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 drive
s, hard disk
s, 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.
Most recent computers that include a parallel port can operate the port in ECP or EPP mode, or both simultaneously. IEEE-1284 requires that bi-directional device communication is always initiated in Nibble Mode. If the host receives no reply in this mode, it will assume that the device is a legacy printer, and enter Compatibility Mode. Otherwise, the best mode that is supported on both sides of the connection is negotiated between the host and client devices by exchanging standardized Nibble Mode messages.
An IEEE-compliant cable must meet several standards of wiring and quality. Three types of connectors are defined:
An IEEE 1284-I device uses IEEE 1284-A and IEEE 1284-B connectors, while an IEEE 1284-II device uses IEEE 1284-C connectors.
In IEEE 1284 Daisy Chain Specification, up to 8 devices can be connected to a single parallel port.
All modes use TTL voltage logic level
s, which limits the possible cable length to a few meters unless expensive special cables are used.
For detailed specifications, including pinouts, refer to the links below.
Interrupt list related to the EPP BIOS calls:
Parallel communications
In telecommunication and computer science, parallel communication is a method of sending several data signals simultaneously over several parallel channels...
between computers and other devices.
History
Centronics
Centronics Data Computer Corporation was a pioneering American manufacturer of computer printers, now remembered primarily for the parallel interface that bears its name.-The beginning:Centronics began as a division of Wang Laboratories...
developed the now-familiar printer parallel port
Parallel port
A parallel port is a type of interface found on computers for connecting various peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port or Centronics port...
that soon became a de facto
De facto
De facto is a Latin expression that means "concerning fact." In law, it often means "in practice but not necessarily ordained by law" or "in practice or actuality, but not officially established." It is commonly used in contrast to de jure when referring to matters of law, governance, or...
standard. The original standard became non-standard itself as enhanced versions of the interface were developed, such as the HP
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...
Bitronics implementation released in 1992. In 1991 the Network Printing Alliance
Printer Working Group
The Printer Working Group charter is to develop standards that make printers, operating systems and applications work better.In 1991 a consortium of printer and network manufacturers formed the Network Printing Alliance...
was formed to develop a new standard. In March 1994, the IEEE 1284 specification was released.
Overview
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
s per second; actual throughput is around 2 megabytes/second, 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
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
interfaces could be produced at a much lower cost. This included scanners
Image scanner
In computing, an image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop scanner where the document is placed on a glass...
, tape drive
Tape drive
A tape drive is a data storage device that reads and performs digital recording, writes data on a magnetic tape. Magnetic tape data storage is typically used for offline, archival data storage. Tape media generally has a favorable unit cost and long archival stability.A tape drive provides...
s, hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
s, 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:- Compatibility Mode, also known as Centronics, standard or SPP, is a uni-directional implementation with only a few differences from the original Centronics design. This mode is almost exclusively used for printers. The only signals that the printer can send back to the host are some fixed-meaning status lines that signal common error conditions, such as the printer running out of paper.
- NibbleNibbleIn computing, a nibble is a four-bit aggregation, or half an octet...
Mode is an interface that allows the device to transmit data four bits at a time, (re)using four of the status lines of Compatibility Mode for data. This is the Bi-tronics mode introduced by HPHewlett-PackardHewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...
and is generally used for enhanced printer status. Although never officially supported with these, Nibble Mode works with most of the pre-IEEE-1284 Centronics interfaces as well. - Byte Mode, also known as "Bi-Directional" (although all modes except Compatibility Mode are in fact bi-directional), is a half-duplex mode that allows the device to transmit eight bits at a time using the same data lines that are used for the other direction. This mode is supported on a minority of pre-IEEE-1284 interfaces as well, such as those built into the IBM PS/2 computers; because of this, it is sometimes unofficially called the PS/2 mode.
- Enhanced Parallel Port (EPP) is a half-duplex bi-directional interface designed to allow devices like printers, scanners, or storage devices to transmit large amounts of data while quickly being able to switch channel direction. EPP can provide up to 2 MByte/s bandwidth, approximately 15 times the speed achieved with normal parallel-port communication with far less CPU overhead.
- Extended Capability Port (ECP) is a half-duplex bi-directional interface similar to EPP, except that PC implementations use direct memory accessDirect memory accessDirect memory access is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory independently of the central processing unit ....
(usually ISA DMA on channel 3) to provide even faster data transfer than EPP by having the ISA DMA hardware and the parallel port interface hardware handle the work of transferring the data instead of letting the CPU do this work. Many devices that interface using this mode support RLERun-length encodingRun-length encoding is a very simple form of data compression in which runs of data are stored as a single data value and count, rather than as the original run...
compression. ECP can provide up to 2.5 MByte/s of bandwidth, which is the natural limit of 8-bit ISA DMA. http://www.nor-tech.com/solutions/dox/ieee1284_parallel_ports.pdf. An ECP interface on a PC can improve transfers to pre-IEEE-1284 printers as well, by reducing the CPU load during the transfer through the use of the PC's ISA DMA engine. However, reversing channel direction is not quick, so it is unsuitable for devices that frequently switch directions like network adapters and storage adapters.
Most recent computers that include a parallel port can operate the port in ECP or EPP mode, or both simultaneously. IEEE-1284 requires that bi-directional device communication is always initiated in Nibble Mode. If the host receives no reply in this mode, it will assume that the device is a legacy printer, and enter Compatibility Mode. Otherwise, the best mode that is supported on both sides of the connection is negotiated between the host and client devices by exchanging standardized Nibble Mode messages.
An IEEE-compliant cable must meet several standards of wiring and quality. Three types of connectors are defined:
- DB-25D-subminiatureThe D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smaller connectors used on computer systems....
(type A) for the host connection. - CentronicsMicro ribbonThe micro ribbon or miniature ribbon connector is a common type of electrical connector used particularly in computer and telecommunications applications. Popularly referred to as a Centronics connector due to the widely used Centronics parallel interface, it is also known as a Telco, Amphenol,...
(officially called "Micro Ribbon", type B) 36 pin for the printer or device connection. - Mini-Centronics (type C, MDR36) 36 pin, a smaller alternative for the device connection that has not proven popular.
An IEEE 1284-I device uses IEEE 1284-A and IEEE 1284-B connectors, while an IEEE 1284-II device uses IEEE 1284-C connectors.
In IEEE 1284 Daisy Chain Specification, up to 8 devices can be connected to a single parallel port.
All modes use TTL voltage logic level
Logic level
In digital circuits, a logic level is one of a finite number of states that a signal can have. Logic levels are usually represented by the voltage difference between the signal and ground , although other standards exist...
s, which limits the possible cable length to a few meters unless expensive special cables are used.
For detailed specifications, including pinouts, refer to the links below.
IEEE 1284 standards
- IEEE 1284-1994: Standard Signaling Method for a Bi-directional Parallel Peripheral Interface for Personal Computers
- IEEE 1284.1-1997: Transport Independent Printer/System Interface- a protocol for returning printer configuration and status
- IEEE 1284.2: Standard for Test, Measurement and Conformance to IEEE 1284 (not approved)
- IEEE 1284.3-2000: Interface and Protocol Extensions to IEEE 1284-Compliant Peripherals and Host Adapters- a protocol to allow sharing of the parallel port by multiple peripherals (daisy chaining)
- IEEE 1284.4-2000: Data Delivery and Logical Channels for IEEE 1284 Interfaces- allows a device to carry on multiple, concurrent exchanges of data
IEEE 1284 typical color codes
Here are is the typical colors found on 25-pin IEEE 1284 cable leads.| Pin | Color | Alt Color |
|---|---|---|
| 1 | red | |
| 2 | pink/red | |
| 3 | brown | |
| 4 | orange | |
| 5 | light-blue/yellow | |
| 6 | light-blue/red | |
| 7 | light-blue | |
| 8 | blue | |
| 9 | light-blue/black | green/blue |
| 10 | green | |
| 11 | yellow | |
| 12 | pink/orange | |
| 13 | gray | |
| 14 | gray/green | |
| 15 | pink/blue | orange/white |
| 16 | pink/black | brown/white |
| 17 | light blue/blue | light blue/green |
| 18 | blue-white | |
| 19 | green/black | green/red |
| 20 | pink/white | yellow/black |
| 21 | gray/black | |
| 22 | white/black | gray/yellow |
| 23 | purple | |
| 24 | pink | |
| 25 | white | |
| NC | white/yellow | white/green |
| All | white/purple | red/black |
See also
- LPTLPTLPT is the original, and still common, name of the parallel port interface on IBM PC-compatible computers. It was designed to operate a text printer that used IBM's 8-bit extended ASCII character set. The name derives from the fact that "line printer" was a common generic term at the time for any...
- IFSP
- Parallel portParallel portA parallel port is a type of interface found on computers for connecting various peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port or Centronics port...
- FireWire (IEEE 1394)
- Universal Serial BusUniversal Serial BusUSB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....
- List of device bandwidths
External links
- Warp Nine Engineering's introduction to the IEEE 1284-1994 standard
- Interfacing to the Enhanced Parallel Port
- Undocumented Printing Wiki - IEEE 1284 Standards
- IEEE 1284 - Updating the PC Parallel Port
- IEEE 1284 summary
- IEEE 1284 ports pinouts
- Signal Diagrams for IEEE 1284 Protocol
- Parallel port - LPT (IEEE 1284)
Interrupt list related to the EPP BIOS calls: