Computers as Components, 2nd Edition

3.1 Programming Input and Output 93

The UART is programmable for a variety of transmission and reception parameters.

However, the basic format of transmission is simple. Data are transmitted as streams of

characters, each of which has the following form:

Bit 0

Bit n–1

Time

Start

bit

Stop bit

. . .

Every character starts with a start bit (a 0) and a stop bit (a 1). The start bit allows the receiver

to recognize the start of a new character; the stop bit ensures that there will be a transition at

the start of the stop bit. The data bits are sent as high and low voltages at a uniform rate. That

rate is known as the baud rate; the period of one bit is the inverse ...