英語高手幫忙翻譯下面的一段英文
Apart from all above, you can also get super fast I/O lines using low cost simple TTL or CMOS shift registers.
Communication with external devices over distances of more than a few feet is often done in a serial manner – one bit at a time over one or two lines (one line for receiving information and one for sending). The 8051 family of microcontrollers typically include a Universal Asynchronous Receiver Transmitter (UART) for this purpose. This is the same type of device used to implement the COM ports of a PC. Although it is possible to use simple software polling routines to service a UART, it wastes CPU time and prevents the CPU from performing other tasks, so interrupts are more commonly used. In this lab, you will design a program to send and receive serial data using interrupts. A UART device driver can be difficult to debug using standard software-simulation tools. In such cases, it is common to develop models that simulate external hardware and allow you to see how your hardware-software design will interact with this hardware. A model of an external serialdevice will be provided which you can connect to the 8051 and can use to simulate and debug your design in hardware.
A UART (Universal Asynchronous Receiver-Transmitter) provides all the features needed for simple serial communications. It is bi-directional in the sense that it can both send and receive data. Initializing the 8051 UART is easy: set a timer to program the baud-rate (the rate data is transmitted), enable the timer (turn it on), set the serial port mode, and then set the number of bits to be sent/received. Bytes may be sent or received through an internal register SBUF. When a byte is received, an internal flag, RI (Receive Interrupt), is set. To read the received byte, simply read SBUF. To transmit a byte, simply write it to SBUF.The flag TI (Transmit interrupt) notifies the 8051 when a byte has finished being sent and gives the microcontroller an opportunity to send another byte.
The simplest way to send and receive data is to constantly monitor the flags RI and TI from within your program, but then your program would never have time to do anything else. A better way is to use a serial-port interrupt. The 8051 is set up so that an interrupt can be generated anytime RI or TI is set ― anytime that the UART needs attention. Because the interrupt will be generated on either RI or TI, the function that responds to the interrupt must poll RI and TI to see which of them caused the interrupt.