Types of Serial Cables

by Saifuddin Abdullah
Image by Flickr.com, courtesy of Blake Patterson

Data communication between digital devices is often done through serial cables, which are used to transfer data between devices that use bit-by-bit or serial port communication techniques. Most types of serial cables use RS-232 (Recommended Standard-232) standard interface for communications, which mainly specifies that data must be sent in a predefined sequence of bits. Generally, serial cables are categorized according to their interfaces and standards.


This common serial cable is used between a DTE and DCE--that is, data terminal equipment and data communications equipment respectively. In communications terminology, DTE refers to terminating/initiating point of session and DCE means forwarding point of a communication session. These cables offer both 9-25 and 25-25 pin connections at transmit-receive end connectors. DTE-DCE cables are normally used to establish a connection between computers and modem cards. In this scenario, a computer acts as a DTE and modem card functions as DCE.

Null-Modem Cable

Null-modem is the ideal standard cable to connect two PCs using null-modem configuration. It is called null-modem because it involves no DCE (modem) between DTE-DTE sessions. Moreover, this process uses a certain signal quantity to ensure connection stability between two devices, which is known as "handshaking." A null-modem medium is configured by a serial cable connected to a null-modem adapter, having transmit and receive lines cross-linked. Most common null-modem cables contain 9-9, 9-25 and 25-25 pin configuration at their connectors.

Two-Wire DTE-DCE

This cable is nearly identical to basic DTE-DCE cable, except that no handshaking process is involved between computer and modem. This cable is also available in 9-25 and 25-25 pin configurations, similar to basic DTE-DCE. A limitation of a non-handshaking procedure is the absence of acknowledgment from the DTE end.

V.35 Crossover

The V.35 crossover interface is used to connect DTE-DTE and DCE-DCE nodes. It also provides enhanced data rate as high as 64 kbps, by providing 34-34 pin configurations at both transmitter and receiver ends. This particular medium is a mixture of RS-232 and RS-449 standards. Its successors in RS-232 and RS-449 standard domains include V.28 and V.11, respectively.

Serial Printer

Serial printer cables are used to establish connection between a computer and printer through a serial port. This cable is configuration specific; that is, a 9-25 pin cable is used when both printer and computer act as DTE and a 25-25 pin cable is used when computer and printer act as DTE and DCE, respectively. When both devices are DTE, a null-modem cable can work; however, if a serial printer is connected to a computer through it, it is ineffective.


Photo Credits

  • Image by Flickr.com, courtesy of Blake Patterson

About the Author

Working from New York City, Saifuddin Abdullah is a freelance writer and linguist. With expertise in communications, electronics and mathematics, he has written for projects including WritingBee and Paktranslations MLT. Abdullah holds a bachelor's degree in telecommunications engineering from M.A.J. University, Karachi.

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