Serial Cabling Guide

Serial means one event at a time.

It is usually contrasted with parallel, meaning more than one event happening at a time.

In data transmission, the techniques of time division and space division are used, where time separates the transmission of individual bits of information sent serially and space (on multiple lines or paths) can be used to have multiple bits sent in parallel.

In the context of computer hardware and data transmission, serial connection, operation, and media usually indicate a simpler, slower operation and parallel indicates a faster operation. This indication doesn't always hold since a serial medium (for example, fibre optic cable) can be much faster than a slower medium that carries multiple signals in parallel.

On PCs, a printer is usually attached through a parallel (LPT) interface and cable so that it will print faster. The Keyboard and mouse are one-way devices that only require a serial interface and line. Inside computers, much of the circuitry supports bits being moved around in parallel.

Modems use one of the PC's serial connections or COM ports. Serial communication between PC's and modems and other serial devices adheres to the RS232C standard.

Conventional computers and their programs operate in a serial manner, with the computer reading a program and performing its instructions one after the other. However, some of today's computers have multiple processors and can perform instructions in parallel.

RS-232C is a long-established standard ("C" is the current version) that describes the physical interface and protocol for relatively low-speed serial data communication between computers and related devices. It was defined by an industry trade group, the Electronic Industries Association (EIA), originally for teletype devices.

RS-232C is the interface that your computer uses to talk to and exchange data with your modem and other serial devices. Data from the computer is transmitted to an internal or external modem (or other serial device) from its Data Terminal Equipment (DTE) interface. Since data in the computer flows along parallel circuits and serial devices can handle only one bit at a time, the UART chip converts the groups of bits in parallel to a serial stream of bits. As your PC's DTE agent, it also communicates with the modem or other serial device, which, in accordance with the RS-232C standard, has a complementary interface called the Data Communications Equipment (DCE) interface.

The length of serial cables can work across is effected by the baud rate (speed) at which the PC and peripheral are set. The greater the baud rate, the shorter the cable length.

9600 baud will work effectively a 100 Mtrs. 57,600 baud is maximum 20 Mtr.

IBM compatible PC's have either a D9 male or a D25 male connector on the PC

Of course, not all machines are IBM compatible.