Question about UART waveform

[Parineeti]

A UART is configured to transmit 8 bit data, 1 start and 1 stop bit. The serial data output is observed on oscilloscope which looks like a square wave with frequency of 9600Hz. What is the baud rate and transmitted data?

Plzzz answer the above question and explain with formula if any....

 

[KlausST]

Hi,

IT depends on data byte.
UART interface is 1 in idle state.
Start is 0
Data is 0xAA (example)
Stop is 1

Then data stream is like this: 0 10101010 1
Remember that with RS232 a "0" is transmitted as positive voltage and a "1" is transmitted as negative voltage.

Klaus

If you transmit my above example then you need to transmit with baudrate 19200 to see a frequency of 9600 Hz on a scope.

 

[Parineeti]

Explain me how did you get 19200 as baud rate. Please use formula if any...

 

[FvM]

Explain me how did you get 19200 as baud rate. Please use formula if any...

I don't see how a formula would help you with this simple homework excercise. You better get you pencil and paper and sketch the waveform. And compare with the explanation of UART operation in your text book.

To give an additional hint, consider that the bit time must be equal to a half period of the square wave.