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Parallel connector pin assignment

Printer cable

Interlink cable

Windows 95/98/ME DCC

Parallel test plugs

Parallel cables

Standard parallel cables are easy to obtain, but the link cable and test connectors which are shown here can often be better soldered by yourself.

Parallel connector pinout

The parallel port socket on your computer uses 25 pins. On most peripherals like printers, the 36 pins Centronics version is used. Both connector pinouts are shown here. The centronics socket is named after the company that introduced the first dot matrix printer in 1970, but after IBM and Epson took over the dot matrix printer market (later followed by Hewlett Packard in the laser and deskjet printer segment) most people only associate the word centronics with the port interface itself, not with a manufacturer.

Parallel DB25 pinout

Centronics pinout

Parallel printer cable

Most printers are connected to a computer using a cable with a 25 pins DB male connector at one side and a 36 pins centronics connector on the other. The normal way to make such a cable is shown here.

Parallel printer cable

Line	DB 25 male (computer)		Centronics (printer)
Strobe	1		1
Data bit 0	2		2
Data bit 1	3		3
Data bit 2	4		4
Data bit 3	5		5
Data bit 4	6		6
Data bit 5	7		7
Data bit 6	8		8
Data bit 7	9		9
Acknowledge	10		10
Busy	11		11
Paper out	12		12
Select	13		13
Autofeed	14		14
Error	15		32
Reset	16		31
Select	17		36
Signal ground	18		33
Signal ground	19		19 + 20
Signal ground	20		21 + 22
Signal ground	21		23 + 24
Signal ground	22		25 + 26
Signal ground	23		27
Signal ground	24		28 + 29
Signal ground	25		16 + 30
Shield	Cover		Cover + 17

Interlink and Windows 95/98/ME DCC parallel cable

The following parellel cable can be used with file transfer and network programs like LapLink and InterLink. The cable uses the parallel port which makes it possible to achieve higher throughput than with a serial connection at the same low costs. The cable is amongst others compatible with the following software.

• Laplink from Travelling software
• MS-DOS v 6.xx InterLink
• Windows 95, 98 and ME direct cable connection
• Norton Commander
• Norton Ghost

Because the parallel port on a computer was mainly designed to connect printers with one-way communication, a trick is used to achieve full two way data transfer between both sides. Five error and status message inputs are redefined as data inputs. Instead of reading full bytes, the communication software reads these five bits and combines multiple groups of data back to bytes. The sender and receiver have to use the same protocol to convert bytes to groups of 5 bits and vice versa.

Interlink and Windows 95/98/ME DCC parallel cable

Connector 1	Connector 2	Description
2	15	Data bit 0		Error
3	13	Data bit 1		Select
4	12	Data bit 2		Paper Out
5	10	Data bit 3		Acknowledge
6	11	Data bit 4		Busy
10	5	Acknowledge		Data bit 3
11	6	Busy		Data bit 4
12	4	Paper Out		Data bit 2
13	3	Select		Data bit 1
15	2	Error		Data bit 0
25	25	Signal ground

Parallel port test plugs

Both Norton Diagnostics and CheckIt have the ability to check the functionality of a parallel port. To do this, both software packages need a special plug on the port. Unfortunately, the pin layout of both connectors is not the same. The scheme of both sockets is given here.

Norton test plug

CheckIt test plug

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