What is a Null Modem Cable?

It is a cable wiring which is used with a program (Laplink) and allows two computers to be connected and to communicate without a modem.Physically is a cable which has two DB25(25 pin) Female connectors and each of them plugs into the serial port (RS232) of each computer There are many types of connections of the Null Modem Cable.

• · It allows you to connect one PC to another nearby PC or serial device using its modem protocol.
• · It is frequently used for setting up "head-to-head" gaming between two players at different computers in the same room.
• · The transmit and receive signals are crossed.
• · A null modem cable is limited to 30 feet in length
• · Allows two devices to communicate without a modem.
• · The transmit and receive signals are crossed.
• · A null modem cable is limited to 30 feet in length.

You will need two DB25 connectors (one Male and one Female).

Wire each pin of the connector with the one indicated below

Here you can see the wiring of the cable

RS-232 Serial Null Modem Cable Connections

From	DB25 Female	To	DB25 Female
Connect Pin	2	To Pin	3
Connect Pin	3	To Pin	2
Connect Pin	7	To Pin	7
Connect Pin	4	To Pin	5
Connect Pin	5	To Pin	4
Connect Pin	6	To Pin	20
Connect Pin	20	To Pin	6

RS232 Serial Null Modem (Connercial Adaptor – Kat.)

From	DB25 Female	to	DB25 Male
Pin	1	Pin	1
Pin	2	Pin	3
Pin	3	Pin	2
Pin	4,5	Pin	4,5
Pin	6	Pin	20
Pin	7	Pin	7
Pin	8	Pin	20
Pin	11	Pin	12
Pin	12	Pin	11
Pin	20	Pin	6,8

Note!! All other pins are unused

All about Null Modem Cable,and laplink

http://waami.avmz.uni-wuppertal.de/HwB/menu_Cable.html

http://www.pccables.com/cabtech.htm

http://www.xensei.com/users/jeffm/www/pinouts.html