Software can then read the receive register which removes the data and allows the next byte of data to be shifted in.Ī UART can have additional registers that allow software to configure the behavior of the UART. The status register also will have a status bit that indicates when a new byte of data has been received. When the transmit register is empty, the next byte of data can be loaded into the transmit shift register. Software examines the status registers to determine when the transmit shift register is empty. In addition to the shift registers, there will be one or more status registers. Two separate shift registers allows a UART to transmit and receive data at the same time. The Rx and Tx pins are normally connected to separate shift registers (one for shifting data out and one for shifting data in).

When two devices are connected using a UART, the Rx pin of one device is connected to the Tx pin of the second device. The UART interface consists of two pins: the Rx and Tx pin. The UART can provide input/output to a terminal program that allows the user to monitor status and provide input. UARTs are commonly used to interface with devices that have no graphical display capabilities. The term UART stands for Universal Asynchronous Receiver/Transmitter. The serial interface we will examine here is called a UART. Reducing the number of pins also makes printed circuit board (PCB) development much easier since there are far fewer pins to route between devices. If we need our data to be 32 bits instead of 8 bits, we simply need additional clock cycles. Using a small number of pins, we can transmit data of any size. The motivation behind using serial interfaces is that a serial interface consists of only a few pins. Adding additional pins to a devices increases the material costs and physical size of a microprocessor. Parallel buses are very fast, but they require a large number of external pins for a single interface. So why would we use a serial interface as compared to a parallel interface? If we want to transfer a 32-bit value using a parallel interface, we need a minimum of 32 pins on the microprocessor. After the parallel load, data is shifted out one bit at a time, starting with the least significant bit. The illustration below shows how the data is loaded using a parallel load into a shift register. So what is a serial interface? At a very basic level, a serial interface is a shift register that shifts data in/out one bit at a time. This data is often transmitted over a serial interface. An example would be a digital temperature sensor reporting the ambient temperature of the room to the the main microprocessor. Embedded systems often require communication between integrated circuits.

Uart serial communication basics