UART is an asynchronous communication protocol. A complete UART signal package must consists of START, DATA, Parity check, STOP, Buad, and TXD segments.

	UART Specification user-defined interface:

	START	When TXD is changing form HIGH to LOW voltage (1 bit).
	DATA	Users must decide the size of signal package segment from 4 to 8bits.
	Parity Check	This performs three types of parity checks: odd-parity, even-parity, and no-parity.
	STOP	This occurs when TXD is at high voltage. This is adjustable; this is commonly set to 1 or 2.
	Baud	This is the data transmission speed according to the START initial condition.
	TXD	This is the transmission direction. It is LSM -> MSB by default.