![]() ![]() So, instead of using time as a way to synchronize the bits, the data format is used. Using the asynchronous protocol, each device uses its own internal clock resulting in bytes that are transferred at arbitrary times. Synchronous communications allows faster data transfer rates than asynchronous methods, because additional bits to mark the beginning and end of each data byte are not required. That is, each bit that is sent is either actual data or an idle character. Even when actual data is not really being sent, a constant flow of bits allows each device to know where the other is at any given time. The two devices initially synchronize themselves to each other, and then continually send characters to stay synchronized. ![]() Using the synchronous protocol, all transmitted bits are synchronized to a common clock signal. The RS-232 standard supports two types of communication protocols: synchronous and asynchronous. Synchronous and Asynchronous Communication For more information about reading and writing values, refer to Writing and Reading Data. For example, if you read one value from a device using the int32 format, then that value consists of four bytes. When reading or writing data, you might need to specify a value, which can consist of one or more bytes. Moreover, eight data bits are always used regardless of the number of data bits specified for transmission, with the unused bits assigned a value of 0. However, when serial data is stored on your computer, the framing bits are stripped away, and only the data bits are retained. At first, this term might seem inaccurate because a byte is 8 bits and the serial data format can range between 7 bits and 12 bits. ![]() ![]() The collection of bits that comprise the serial data format is called a byte. The remaining bits are called framing bits because they frame the data bits. The data bits are often referred to as a character because these bits usually represent an ASCII character. Number of data bits - parity type - number of stop bitsįor example, 8-N-1 is interpreted as eight data bits, no parity bit, and one stop bit, while 7-E-2 is interpreted as seven data bits, even parity, and two stop bits. The format for serial port data is often expressed using the following notation The diagram below illustrates the serial data format. A parity bit and an additional stop bit might be included in the format as well. The serial data format includes one start bit, between five and eight data bits, and one stop bit. Serial Port I/O (External Interfaces/API) External Interfaces/API ![]()
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