UART data speed is measured by baud rate which is defined as number of symbols per second
Baud Rate is dependent on the clock inside the controller. Stability of the controller is important to get accurate baud rate
When there is no transmission on the UART line, pins are in HIGH state
UART communication starts with a START bit which is a LOW bit
UART internally has a serial register/FIFO to collect the data
UART frame also includes parity bit indicates the number of HIGH in the data
There are several registers inside the controller IC to control the UART communication
UART data is received by the controller using interrupt mechanism. This meant whenever there is data on the UART pins, interrupt shall be raised and controller executed the UART ISR
If the parity bit is HIGH then the parity is ODD that means there are odd number of HIGH in the data bits
If the parity bit is LOW then the parity is ODD that means there are odd number of HIGH in the data bits
LSB of the data (D0) is transmitted first
UART is for on-board communication
If we want to use UART for communicating outside the board, RS232 transceiver must be used. An example, RS232 transceiver (MAX232 IC) is as shown below.
For RS232 signalling, any voltage above +5V is treated as LOW and any voltage below -5V is treated as HIGH
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