IEEE-1284 Description

The IEEE-1284 bus defines a parallel printer bus specification with speeds above 1MBps. IEEE-1284 defines a Point-To-Point asynchronous bi-directional interface. Devices may be either 1284 compatible {the older parallel port devices} or 1284 compliant. The maximum recommended length for a printer cable is 25 feet [up to 32 feet maximum]. Centronics parallel cables run out to 12 feet. The IEEE1284 cable replaced the 'Centronics' cable which is obsolete.

An IEEE1284 or Centronics interface will be indicated by the printer having an LPT port [line printer terminal], which normally refers to a parallel port. The LPT port would be a Centronics interface before the mid 1990's or an IEEE1284 after the mid 1990's. However as of 2005 a printer may not have an LPT port, but instead have a USB port and or a Network port with Ethernet. An Ethernet port will normally be found over an RJ-45 jack.

IEEE-1284 operates in five different modes: [The connector or cable does not change with each different mode, but the function of some of the pins do]

Level II Driver / Receiver Interface Circuit

To maintain the compatibility with the original Centronics port which uses open collector drivers, pull-up resistors (Rp) are required to transmit logic high levels. The established common standard resistor values of 2.2kOhms or 4.7kOhms. Control and Status lines only require a pull-up resistor (Rp). The data lines and Strobe pin may require a series resistor (Rs) for termination to match the impedance for the 8 bi-directional data lines and the strobe. The series termination value is adjusted so that the addition of the resistor and the driver impedance equal 45 Ohms to 55 Ohms cable impedance. So a driver IC with a nominal impedance of 15 ohms would require a 33 ohm [standard value] resistor to comply with IEEE1284.

Level II Transceiver Interface Circuit

The Driver has a slew rate of 0.05v/nS - 0.40v/nS, with an impedance of 50 ohms +/- 5 ohms at half of Voh
The maximum output voltage is +5.5v, the minimum voltage is -0.5v.
The steady state high output is +2.4v [minimum] with 14mA of source current
The steady state low-level output is +0.4v [maximum] with a source current of 14mA

The Receiver will operate with a maximum input voltage is +7.0v, the minimum voltage is -2.0v.
The steady state high input is +2.0v [minimum] with 20uA of source current
The steady state low-level input is +0.8v [maximum] with a source current of 20uA
The Receiver has needs to provide between 0.2v and 1.2 volts of input hysteresis

The 1284 standard defines two levels of interface compatibility, Level I and Level II. The Level I interface is defined for products that are not going to operate at the high speed advanced modes, but need to take advantage of the reverse channel capabilities of the standard. The Level II interface is for devices that will operate in the advanced modes, with long cables, and at the higher data rates.

Compatibility mode; Centronics type operation (PC to Peripheral), providing the original (required) control signaling bits. These bits include 8 data lines, a Strobe, a Busy, an Acknowledge, a Select, Paper Empty, Fault, Initialize Printer, Select Printer, and a Auto Feed line. Compatibility mode is the basic mode of operation, asynchronous, byte wide operation with a transfer rate of between 50kBps to 150kBps.

Nibble mode; 4 bit data bus (Peripheral to PC), 8 bit data bus (PC to Peripheral); supporting uni-directional printer interfaces. This provides an interface which operates full speed forward and half speed in reverse. The transfer rate is between 50kBps to 150kBps

Byte mode; 8 bit bi-directional bus. Normal port operation. The transfer rate is between 50kBps to 150kBps

ECP; Extended Capabilities Port. Allowed the PC to send 32 bit data to the port, than letting the port divide up the data into four 8 byte messages, improving system (PC) operation. Transfer speeds are ten times faster then the previous modes.

EPP; Enhanced Parallel Port; Allows high-speed transfers of bytes in either direction. EPP is used with real time controlled peripherals. EPP transfer times are the same as ECP transfer rates.

IEEE-1284 Bus Interface ICs

Because the minimum output driver voltage is 2.4v, either +5v or +3.3v Low Voltage TTL logic devices may be used.

IEEE1284 Transceiver (74ACT1284, 74LVX161284) {Fairchild Semiconductor}

Parallel port termination networks {STMicroelectronics}

[74ACT1284, 74LVC161284, 74LV161284] 7-19 bit interface transceiver with termination, {Texas Instruments, TI}

Flow-through pin configuration allows easy interface between the "Peripheral and Host"

IEEE-1284 Connector Manufacturers

1284-A: Female 25 pin D connector [Host connector, PC side]
1284-B: Female 36 pin ribbon connector (.0850 center line) Centronics, Bale locks [Peripheral connector, Printer side]
1284-C: Female 36 pin ribbon connector (.050 center line) mini-Centronics, Clip latches [Host and Peripheral connector]

Manufacturers: (Type A) AMP 747846-4, Molex 82009, and 3M Company
Manufacturers: (Type B) Amphenol AMP 747846-4, Molex 82009, and 3M Company
Manufacturers: (Type C) AMP 2-175925-5, Harting 60-11-036-512, Molex 52311-3611, and 3M 10236-52A2VC

3M
Tyco/Electronics "Amp"
Amphenol
Molex

IEEE-1284 Pinout

Straight-through Cables
Parallel Cable Port Pinout
Centronics Cable Pin-out
1284-A Cable Pinout
1284-B Cable Pinout
1284-C Cable Pinout


Adaptor Cables
IEEE1284-A to 1284-B Adaptor Pinout
IEEE1284-A to 1284-C Adaptor Pinout
IEEE1284-B to 1284-C Adaptor Pinout

USB to IEEE-1284 Adaptors are possible.

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