IEEE1284-A to IEEE1284-C Adaptor Pin-Out

IEEE1284-A to IEEE-C Cable Adaptors

The IEEE-1284 'A' cable is backwards compatible with the IBM Personal Computer [PC] Parallel Port cable [Centronics Connector] and has the same pinout listed in column 1 . The IEEE-1284 'C' cable pin-out assignments are shown in column 3. The connector for IEEE-1284 'A' is a 25 Pin D-Sub while the connector for IEEE-1284 'C' is a Male Mini Centronics [MDR36] 36 pin connector. This adaptor cable is used to interconnect a device with an 'A' connector with one that uses a 'C' connector

The Original IBM PC Parallel Port, also called the LPT port [defined as the IEEE-1284 'A' cable], was replaced by the IEEE-1284 standard, and is a better made cable.

IEEE1284 adaptors never seemed to see wide spread usage during the half a dozen years IEEE-1284 was being used.
The first column provides the signal assignments for the Host or PC side while the last column provides the signal assignments for a peripheral [printer].
The middle column provides the signal names, or function, for the interconnecting lines used by either side of the cable.

IEEE 1284-A to 1284-C Adapter PinOut
Host A connector Function Peripheral C connector
1 nStrobe 15
2 Data bit 1 6
3 Data bit 2 7
4 Data bit 3 8
5 Data bit 4 9
6 Data bit 5 10
7 Data bit 6 11
8 Data bit 7 12
9 Data bit 8 13
10 nAck 3
11 Busy 1
12 PError 5
13 Select 2
14 nAutoFd 17
15 nFault 4
16 nInit 14
17 nSelectIn 16
18 Pin 1 (nStrobe) ground return 33
19 Pins 2 and 3 (Data 1 and 2) ground return 24, 25
20 Pins 4 and 5 (Data 3 and 4) ground return 26, 27
21 Pins 6 and 7 (Data 5 and 6) ground return 28, 29
22 Pins 8 and 9 (Data 7 and 8) ground return 30, 31
23 Pins 11 and 15 ground return 19 and 22
24 Pins 10, 12, and 13 ground return 20, 21, and 23
25 Pins 14, 16, and 17 ground return 32, 34, and 35

Personal Computer [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 The IEEE1284 cable replaced the 'Centronics' cable, the Centronics cable is obsolete.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]. Note that the newer interface [right column] uses one ground pin per data line, while the older interface [left column] only uses one ground pin per data line.
More ground returns and having a separate ground per data line tends to produce a signal with lower noise.

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.

Centronics Connector Pinout .. Parallel Port Connector Pinout .. 1284-A Cable Pinout .. 1284-B Cable Pinout .. 1284-C Cable Pinout

Back to the main IEEE-1284 bus page.
The IEEE-1284 page discusses the actual electrical and physical interface.

The IEEE1284 cabling interface started to become out-dated around mid 2005 when Ethernet ports began showing up on printers.
Soon after that USB connections also began to show up, either by them selves to together with Ethernet interfaces.
Once that occurred the usefulness of the IEEE1284 connector began to fad, as either of the other connectors are smaller and the interfaces faster.

Editor note; as of 2011 I have to assume that the IEEE1284 committee has disbanded, with no updates to follow.
As a general statement this peripheral bus or cable interface should be considered obsolete and not suited for new development.
However, check the cable assembly page for vendors that still produce cabling gear for a Parallel interface.
Check the COTS card page for other manufacturers which may also be producing expansion cards with an IEEE1284 connector.

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Modified 3/05/12
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