#TRANSMIT DATA SERIAL#

The data frame contains the actual data being transferred. When the receiving UART detects the high to low voltage transition, it begins reading the bits in the data frame at the frequency of the baud rate. To start the transfer of data, the transmitting UART pulls the transmission line from high to low for one clock cycle. The UART data transmission line is normally held at a high voltage level when it’s not transmitting data. Each packet contains 1 start bit, 5 to 9 data bits (depending on the UART), an optional parity bit, and 1 or 2 stop bits: UART transmitted data is organized into packets. Finally, the receiving UART transfers the data packet in parallel to the data bus on the receiving end: The receiving UART then converts the data back into parallel form and removes the start bit, parity bit, and stop bits. The receiving UART reads the data packet bit by bit at its Rx pin. Next, the data packet is output serially, bit by bit at the Tx pin. After the transmitting UART gets the parallel data from the data bus, it adds a start bit, a parity bit, and a stop bit, creating the data packet. Data is transferred from the data bus to the transmitting UART in parallel form. The data bus is used to send data to the UART by another device like a CPU, memory, or microcontroller. The UART that is going to transmit data receives the data from a data bus. The baud rate between the transmitting and receiving UARTs can only differ by about 10% before the timing of bits gets too far off.īoth UARTs must also must be configured to transmit and receive the same data packet structure. Both UARTs must operate at about the same baud rate. Baud rate is a measure of the speed of data transfer, expressed in bits per second (bps). When the receiving UART detects a start bit, it starts to read the incoming bits at a specific frequency known as the baud rate. These bits define the beginning and end of the data packet so the receiving UART knows when to start reading the bits. Instead of a clock signal, the transmitting UART adds start and stop bits to the data packet being transferred. UARTs transmit data asynchronously, which means there is no clock signal to synchronize the output of bits from the transmitting UART to the sampling of bits by the receiving UART. Data flows from the Tx pin of the transmitting UART to the Rx pin of the receiving UART: Only two wires are needed to transmit data between two UARTs.

#TRANSMIT DATA SERIAL#

The transmitting UART converts parallel data from a controlling device like a CPU into serial form, transmits it in serial to the receiving UART, which then converts the serial data back into parallel data for the receiving device. In UART communication, two UARTs communicate directly with each other. One of the best things about UART is that it only uses two wires to transmit data between devices. The principles behind UART are easy to understand, but if you haven’t read part one of this series, Basics of the SPI Communication Protocol, that might be a good place to start. A UART’s main purpose is to transmit and receive serial data.

It’s not a communication protocol like SPI and I2C, but a physical circuit in a microcontroller, or a stand-alone IC. UART stands for Universal Asynchronous Receiver/Transmitter.

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