Question

Sketch the waveform of the letter g when it is transmitted via the USART interface, using the format of 1 start bit, 8 data bits and 1 stop bit

Answer 1

USART-(Universal Synchronous Asynchronous Receiver Transmitter)

• Can interface (2.0B active)
• Two I2C fast mode plus (1 Mbit/s)with 20 mA current sink ,SMBus/PMBus,wakeup for STOP
• Up to five USART/UARTs (ISO 7816 INTERFACE ,LIN ,IrDA,modem control)
• Up to three SPIs,Two with multiplexed I2S interface, 4 to 16 programmable bit frame
• USB 2.0 full speed interface
• Infrared transmitter

Why Serial Communication?

• Parallel communication implies sending a whole byte (or more) of data over multiple parallel wires
• parallel data transfer requires many inputs &outputs pins.This requirement prevents the microcontroller from interfacing with many devices as desired in the application
• Data synchronization for parallel transfer is difficult to achieve over a long distance.
• Serial communication implies sending data bit by bit over single wire
• many I/O devices do not have high data rate to justfiy the use of parallel data transfer.
• consider cost.
• There are 2 types of serial communication:

1. Asynchronous
2. synchronous

Asynchronous Serial Communication

• With asynchronous communication , the transmitter and reciever do not share a common clock

The Transmitter	The Reciever
Shifts the parallel data onto the serial line using its own clock	Extracts the data using its own clock
Also adds the start, stop and parity check bitd	Converts the serial data back to the parallel form after stripping off the start,stop and parity bits

Data format fot Asynchronous Data ommunication

• Data is transmitted character by character bit-serially.
• A character consists of
• one start bit
• 7 or 8 data bits
• an opitional parity bits
• one or one and a half or two stop bits(1)
• least significant bit is transmitted first
• most significant bit is transmitted last

LSB MSB   

start bit

0

1

2

3

4

5

6

7

stop bit 1

stop bit 2