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This page defines an intermediate interface to bridge the gap during the transition from Centronics obsolescence to IEEE1284 adoption.
The IEEE-1284 interface
is defined in the IEEE standard and is a better made cable than the older Centronics interface it replaced.
The original parallel port cable had no specification at all.
The IEEE-1284 interface defined three different connector styles; A, B, and C.
The IEEE-1284 'A' connector defines a 25-pin D-Sub connector.
The IEEE 1284-B connector is
designed to replace the Centronics connector.
The IEEE 1284-B:
connector is a Female 36 pin ribbon connector (.0850 center line)
Centronics, Bale locks [Peripheral connector, Printer side].
The Original IBM PC [LPT] Parallel Port Pin-Out is defined as the 'A' connector in the IEEE1284 interface.
This adapter translated the Centronics pin-out into the IEEE1284 pin out.
However the Centronics interface is obsolete and the IEEE1284 interface is out-dated.
Most adapters sold after 2010 are produced to adapt the Centronics interface to the USB interface,
or to adapt the IEEE1284 interface to the USB interface, but not to adapt a Centronics interface to IEEE1284 interface.
| Host A connector | Function | Peripheral B connector |
| 1 | nStrobe | 1 |
| 2 | Data bit 1 | 2 |
| 3 | Data bit 2 | 3 |
| 4 | Data bit 3 | 4 |
| 5 | Data bit 4 | 5 |
| 6 | Data bit 5 | 6 |
| 7 | Data bit 6 | 7 |
| 8 | Data bit 7 | 8 |
| 9 | Data bit 8 | 9 |
| 10 | nAck | 10 |
| 11 | Busy | 11 |
| 12 | PError | 12 |
| 13 | Select | 13 |
| 14 | nAutoFd | 14 |
| 15 | nFault | 32 |
| 16 | nInit | 31 |
| 17 | nSelectIn | 36 |
| 18 | Pin 1 (nStrobe) ground return | 19 |
| 19 | (Data 1 and 2) ground return | 20, 21 |
| 20 | (Data 3 and 4) ground return | 22, 23 |
| 21 | (Data 5 and 6) ground return | 24, 25 |
| 22 | (Data 7 and 8) ground return | 26, 27 |
| 23 | Pins 11 and 15 ground return | 29 |
| 24 | Pins 10, 12, and 13 ground return | 28 |
| 25 | Pins 14, 16, and 17 ground return | 30 |
The signal names in the table above relate to the Centronics interface.
Although they were defined in the IEEE1284 interface in Compatibility mode.
The PC Parallel printer bus specification 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.
Centronics parallel cables run out to 12 feet. The IEEE1284 cable
replaced the 'Centronics' cable which is obsolete.
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]
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, asychronous, 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.
Return to the main IEEE-1284 bus page.
Centronics Connector Pinout .. Parallel Port Connector Pinout .. 1284-A Cable Pinout .. 1284-B Cable Pinout .. 1284-C Cable Pinout
Note; the table above defines pin out that is out-dated or is in decline.
Obviously the pinout may still be used if required to support a fielded system or legacy product.
However the interface itself is obsolete and should not be designed into a current product line.
The parallel printer bus specification was effectively designed out of printers and peripherals back in 2005
Of course as peripherals no longer used the IEEE1284 interfaces, computers no longer needed to support the interface.
In fact the terms Parallel port or LPT are seldom used with PCs these days.
In the event that a device still has a parallel port, a USB adaptor may be purchased to translate the out-dated physical interface.
As of 2011 many companies sell IEEE1284 to USB Adaptors.
As this specification is out-dated and no longer being updated or worked on by any stands organization.
The pinouts can be considered fixed in place, and will not change.
The editor does not recommend using the IEEE-1284 interface, the standard is obsolete and out-dated.
Although the interface itself is relatively inexpensive, questions should arise if it turns up on either a new PC or peripheral device.
That is not to ignore the thousands of PCs still in service that may still use the IEEE-1284 connector.
Navigation: Engineering Home > Interface Buses > Cabled Interface Standards > IEEE-1284 Standard > A-Cable to B-Cable.
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