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2006-05-28 14:43:18
This chapter provides information on asynchronous communication standards, hardware, terminology, and concepts used throughout this book.
To understand serial ports, consider:
Serial ports are used to physically connect asynchronous devices to a computer. They are located on the back of the system unit, using the multiport adapter, such as, the 8-, 16-, 64- and 128-port asynchronous adapters and the 7318 terminal servers.
To understand the functionality of a serial port, it is necessary to first examine the parallel communications. A standard parallel port uses eight pins, or wires, to simultaneously transmit the data bits, making up a single character. The following shows the parallel transmission of the letter a.
Serial ports require only a single pin, or wire, to send the same data character to the device. To accomplish this, the data is converted from a parallel form (sent by the computer), to a sequential form, where bits are organized one after the other in a series. The data is then transmitted to the device with the least significant bit (or zero-bit) sent first. Once received by the remote device, the data is converted back into parallel form. The following 管理员在2009年8月13日编辑了该文章文章。
