An Introduction to the Technology of Serial Communications

Most of us have got conventional serial ports on our PCs, or have used them at times, but because they are a well-established part of our systems, the sophistication of serial ports is easy to ignore. However, understanding how a serial port works makes troubleshooting and optimizing serial connections a whole lot easier. In fact, understanding the way serial communications works sheds light on a number of diverse communications technologies, including USB and PCIe, that have serial data transmission at their cores.

Put in the simplest terms, a serial port (as the name "serial" indicates) transmits a byte of data by breaking it into its constituent bits, then packaging it so that the byte can be successfully identified and reassembled by the receiving serial port. This process is called “framing” the byte.

Next, the byte is transmitted through the wires of the serial connection. In addition, the serial connection also manages the way data is handled between the computer's CPU and the buffering hardware of the serial connection. This buffering hardware temporarily stores bytes that are in transit, so that the CPU is able to operate with a minimum of interruptions, and so that the serial connection has fewer input/output overrun errors. All of this happens in circuitry called a Universal Asynchronous Transmitter-Receiver, or UART, which will be discussed in more detail as we go along.

Finally, the serial data is received at the other end, and reassembled to be what it once was — bytes of data ready for the computer to understand.

Even this simplistic and short overview gives an indication that the serial port is more than a simple connector: it is actually a complex and effective data transmission system, with mechanical, electrical, and electronic aspects.  The next few articles will draw out these various aspects to give a fuller picture of what a serial port really is and how you can use yours.

All About Serial

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