USART or UART

As a technique processes data in parallel,the data to be sent out using serial data transfer technique must be converted from parallel to serial.similarly,serial data received must be converted into parallel for processing by the computer.A parallel-in-serial out shift register and a serial-in-parallel out shift register can perform this task.In some cases hand shaking signals are also needed.Their purpose is to make sure that a transmitter should not send data faster than it can be received by the receiver. Several programmable ICs are available for serial data transfer.These devices contain all necessary circuitry required for serial data transfer.National INS 8250 has been developed for asynchronous serial data transfer.It is known as universal asynchronous receiver-transmitter(UART).Intel has developed 8251,a universal synchronous-asynchronous receiver-transmitter(USART) which is capable of transmitter data either in synchronous or asynchronous mode.