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 around 2 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:
- Compatibility Mode, also known as Centronics, standard or SPP, is a uni-directional implementation with only a few differences from the original Centronics design.
- Nibble Mode is a uni-directional interface that allows the device to transmit data four bits at a time using status lines for data. This is the Bi-tronics mode introduced by HP and is generally used for enhanced printer status.
- Byte Mode allows the device to transmit eight bits at a time using data lines.
- Enhanced Parallel Port (EPP) is a half-duplex bi-directional interface designed to allow non-printer devices to transmit large amounts of data to the host.
- Extended Capability Port (ECP) is a half-duplex bi-directional interface designed that allows RLE compression.
- DB-25 (type A) for the host connection.
- Centronics (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.
| Transfer mode | (AB cable)/(CC-cable) | |
| Compatibility | 2/10 | 360360 |
| Nibble | 2/10 | 3174603 |
| Byte | 2/10 | 1369863 |
| EPP | 2/10 | 33333333 |
| ECP | 2/10 | 2.500M |
- ↑ IEEE-1284 Specification itself does not specify minimum guaranteed length for level 2 device, only amount of current, voltage, and pull-up resistant for the lines. In early PC interface, control signals is limited to sinking only 7 mA at 0.8 V, which practically limits cable length to 2 metres.
- ↑ Specification itself only claims transfer rate depends on the speed of the host computer, the driver implementation, and the peripheral being used. However, output pulse is specified to 2 MHz, signals take 5 nanosecond to rise or fall. Listed speeds are confirmed maximum (without compression), calculated based on minimum time needed to completely transfer 1 byte of data and to perform any handshake necessary to start transferring the next byte of data. Ideal line condition is assumed. Timing excludes handshakes for negotiating a transfer mode or busy signal.
For detailed specifications, including pin-outs, 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
See also
External links
- [Warp Nine Engineering's introduction to the IEEE 1284-1994 standard]
- [Howstuffworks- How Parallel Ports Work]
- [IEEE 1284 - Updating the PC Parallel Port]
- [IEEE 1284 summary]
- [Draft IEEE 1284 specification]
- [IEEE 1284 ports pinouts]
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