Question

In UART protocol, how many bits are NECESSARILY added into a data package for the interfacing to be successful? What is the function of those bits?

Answer 1

For a UART to successfully interface, without losing data, each data packet should have 1 START bit, 1 STOP bit and a minimum of 5 DATA bits.

START bit: For UART, a Low-level voltage at the transmitting end, depicts that data is being transmitted. Hence, High Voltage for no data transmission and Low Voltage for active data transmission.
Function - As data transmission begins, the UART detects the High to Low Voltage change and the START bit allows it to start reading data from the data frame.

STOP bit: When the data transmission stops, the voltage level of UART changes from Low to High, for two-bit durations. This signal is detected by the Stop bit.
Function - Stop bit ensures to mark the data read operation as complete and depict the end of data.

DATA bit: 5 to 9 Data bits constitute the data frame. Actual data exists on the data frame.
Function - Data bits are responsible for allowing serial read operation for data to be transmitted to the receiving UART.

PARITY bit: Optional bit. Parity bit defines the oddness of the data ready for transmission.
Function - If the value of data changes, when it is received, the Parity bit is the bit that allows for that change to be seen. The parity bit can either give 0 (for Even number) or 1 (for Odd number).