Network, PS2 & Monitor Cable Pin-Out Reference
Information specific to DCC (Direct Cable Connection) including normal and "Null Modem" cables, etc.
Diagrams and tables below explain parallel, serial, and null-modem configurations. Pay close attention to the "female" versus "male" plugs when considering pinouts. Usually the male connector will be an exact opposite of the female, note that I underlined "usually"
2. BASIC CONCEPTS OF COMPUTER CABLING
Parallel ports consist of only 25 pin port adapters called "DB25" where serial ports can consist of either a 25 pin port adapter called a "DB25" or 9 pin adapter called a "DB9" port adapter. Whether the port is a 9 pin or 25 pin it can accomplish all of the same tasks that serial port communications have been designed for.
Each adapter can be a male type connector with pins or a female type adapter with tiny holes. Generally a PRINTER port, or "LPT" on the back of a workstation is female type adapter and a male DB25 pin cable on it for PRINTER connection.
"COM" ports on devices are usually male for the serial ports but it may not be depending upon the hardware. Below are diagrams of a DB25 and DB9.
3. IBM DB25 and DB9 diagrams.
Note! Diagrams show the view you see if your were to look into the connection from the outside
4. IBM DB25 and DB9 numbering scheme. (Pin numbers)
Each pin has a number assigned to it. When connecting null modem, for example, it is important to know these numbers in order to select the correct cables, or when making your own cables.
5. IBM Serial port Pin Descriptions (Wire name) for each pin number.
For following all connections we may
use these chart for transmission of Data via Serial Port.
Note: In DB25 serial cables
the following numbered pins are NOT USED:
6A. IBM Parallel port Pin Descriptions (Wire name) for each pin number.Data transmissions via Parallel Port
Some cables, ports, or connectors may not connect all grounds. Centronics pins
19-30 and 33 are "twisted pair return" grounds, while 17 is "chassis ground" and
16 is "logic ground"
Needed to make cable:
1. Two DB25 male sockets.
Only eight of the nine pins are used in a null modem even though there are 25 pins on DB25 sockets and 9 on DB9's. You need 8 or 9-wired cable with two DB25-Female pin socket or DB9 Female pin socket or one of both.
9. IBM Normal-Modem Cable pin-outs. (DB25 to DB25) and (DB25 to DB9).
IMPORTANT : Both pin sockets must be of DIFFERENT type. This means that for modem-side of cable we need to use MALE type of DB25 pin. And on CPU side of cable we need to use FEMALE type of DB25 or DB9 pin.
* Shield is OPTIONAL. We easily get cable with 9-wires in it, but not 10 then the shield can be attached with shielded wire.
10.The pin-configuration of Internal Serial Port Cables inside Cabinet.
The pin-configuration of internal serial cables (the one that connects from the motherboard to the case) are different for different motherboards, which come in two types. One with straight pins as in old boards like 286/386/486. Another is twisted style cable like in latest Pentiums. The male DB9 pin is connected to serial port on motherboard with 9 wired cable in following two types. Both Serial ports on motherboard have 10 wires but only 9 of them to connect to male DB9 Serial Pins.
The MALE DB25 pin is connected to serial port on motherboard with 9 wired cable in following diagrams. Both serial ports on motherboard have 10 wires to connect to Male DB25 serial pins as follows
Note: #10 wire from motherboard is an optional line which can be connected to pin 1 of DB25 with no harm. Above are the exact pinouts of the all four types of working serial ports with me for IBM Machines.