A stop bit signals the end of a byte in asynchronous communication, preventing errors and allowing the receiver to be ready for the next byte. Bytes include start and stop bits, and are used to transmit data on the internet. The concept originated from older communication technologies. Without a stop bit, a frame error may occur, requiring IT attention.
A stop bit is a character in an asynchronous communication that lets a receiver know that the transmitted byte is finished. This is central to the way most information is transmitted on the internet. Without a stop bit, it is possible that a recipient’s computer could prompt an error message and make further communication with the sending computer problematic.
Asynchronous communication means that data is transmitted without any external clock. Thus, a receiving computer requires to know when the byte ends in order to be “ready” to receive the next byte. In addition to a stop bit, the other piece of the puzzle is the start bit, which signals the start of new information.
Information transmitted over the Internet is broken down into blocks of data, known as bytes, for transmission. Bytes typically include eight bits of data, plus a start bit and a stop bit for a 10-bit character frame. These bytes are then assembled to present the data in its original context. Bytes can be parts of a computer program or something as simple as words in an email message.
Curiously, while a stop and start bit is normally associated with modern technology, including state-of-the-art data transmission, the two terms have their roots in older communication technologies. For example, teletype machines in the late 19th and early 20th centuries had to be resynchronized after the start of each character, called codes. These codes can often include more than one word. However, after each code was transmitted, a stop bit was also transmitted to indicate to the receiving team that it was time to resynchronize.
In some cases, older teletype machines may have required more than one stop bit. However, in modern asynchronous communication, no more than one stop bit is needed. This may confuse some computer users who come across the Windows communication configuration panel, especially on computers with older operating systems. A myriad of choices are presented, most of which make no sense by today’s data transmission standards.
If there is no stop bit for a computer receiving data, an error message is likely displayed. This error is called a frame error and can be caused by incorrectly formatted bytes. May require the attention of an IT professional. Usually, a framing error is the fault of the transmitting machine, not the receiving one, although it is possible that signal degradation could also cause a framing error.
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