A serial cable is a cable

Cable

A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...

 that can be used to transfer information between two devices using serial communication

Serial communication

In telecommunication and computer science, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels...

. The form of connectors depends on the particular PHY

PHY

PHY is an abbreviation for the physical layer of the OSI model.An instantiation of PHY connects a link layer device to a physical medium such as an optical fiber or copper cable. A PHY device typically includes a Physical Coding Sublayer and a Physical Medium Dependent layer. The PCS encodes and...

 used. A cable wired for connecting two DTE

Data terminal equipment

Data Terminal Equipment is an end instrument that converts user information into signals or reconverts received signals. These can also be called tail circuits. A DTE device communicates with the data circuit-terminating equipment...

s directly is known as a null modem

Null modem

Null modem is a communication method to connect two DTEs directly using an RS-232 serial cable. The name stems from the historical use of the RS-232 cable to connect two teleprinter devices to modems in order to communicate with one another; null modem communication was possible by instead using...

 cable.

Maximum cable lengths

The maximum working length of a cable varies depending on the characteristics of the transmitters and receivers, the baud rate on the cable, and the capacitance

Capacitance

In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...

 and resistance

Electrical resistance

The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

 of the cable. The RS 232 standard states that a compliant port must provide defined signal characteristics for a capacitive load of 2500 pF. This does not correspond to a fixed length of cable since varying cables have different characteristics. Empirically tested combinations of bit rate, serial ports, cable type, and lengths may provide reliable communications, but generally RS 232-compatible ports are intended to be connected by at the most a few tens of metres of cable. Other serial communications standards are better adapted to drive hundreds or thousands of metres of cable

This cable has short transmission distance because of noise limiting the transmission of high numbers of bits per second when the cable is more than 15 meters long. This means that the transmitting and receiving lines are referenced to ground. It is cheap to purchase and is simple to join and connect together. It is suitable for unbalanced data standards. Only one device can be connected to the cable.

See also

• Direct cable connection
  Direct cable connection
  Direct Cable Connection , is a feature of Microsoft Windows that allows a computer to transfer and share files with another computer, via a connection using either the serial port, parallel port or the infrared port of each computer...
  
  
• InterLnk
• LapLink cable
  LapLink cable
  A LapLink cable is a cable that allows one to connect two computers together to establish a direct cable connection. The connection is achieved via the parallel ports on the two computers. No networking hardware such as a network interface card or a modem are required...
  
   (can be seen as a parallel equivalent to a serial null modem
  Null modem
  Null modem is a communication method to connect two DTEs directly using an RS-232 serial cable. The name stems from the historical use of the RS-232 cable to connect two teleprinter devices to modems in order to communicate with one another; null modem communication was possible by instead using...
  
   cable)
• Legacy port
  Legacy port
  A legacy port is a computer port or connector that is considered fully or partially superseded. The replacement ports usually provide the functionality of the legacy ports with higher speeds, more compact design, or plug and play and hot swap for greater ease of use; special USB adapters are often...
  
  
• Network bridge