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Parallel cables pinout and port info

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

Norton Diagnostics parallel port test plug

CheckIt test plug