串列埠模式1、2.ppt

class 4 UART、LCD Control Parallel transmission（8bits/time）fast but it need more transmission lines，it’s disadvantageous for long distance transmission Serial transmission（1bit/time）slow but it need less transmission lines, it’s advantageous for long distance transmission? Synchronous（have the same CLOCK） Asynchronous （have different CLOCK，but usually use communication protocol to make communication) What is UART A universal asynchronous receiver transmitter (usually abbreviated UART ) is a type of asynchronous receiver/transmitter, a piece of computer hardware that translates data between parallel and serial forms. UART is commonly used in conjunction with other communication standards such as EIA RS-232. RS232 RS-232 (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data Terminal Equipment) and a DCE (Data Communication Equipment). It is commonly used in computer serial ports. 由於RS-232在傳送資料時，並不需要另外使用一條傳輸線來傳送同步訊號，就能正確的將資料順利傳送到對方，因此叫做「非同步傳輸」，簡稱UART (Universal Asynchronous Receiver Transmitter) 比起「同步傳輸」的方式，可以節省一條傳輸線。 節省一條傳輸線的代價，是必須在每一筆資料的前後都加上同步訊號，把同步訊號與資料混和之後，使用同一條傳輸線來傳輸。 8051 UART(1) 8051 includes an on-chip serial port that can operate in several modes over a wide range of frequencies. The essential function of the serial port is to perform parallel-to-serial conversion for output data, and serial-to-parallel conversion for input data. Hardware access to the serial port is through the RXD and TXD pins (P3.0 P3.1) 8051 UART(2) The serial port feature full duplex operation and receive buffering, allowing one character to be received and held in a buffer while a second character is received. If the CPU reads the first character before the second is fully received, data are not lost. The serial port buffer at address 99H is really two buffers. Writing to SBUF loads data to be transmitted, and reading SBUF accesses received data. 8051 UART(3) The serial port frequency of operation, or baud rate, can be fixed or