How to determine the time base

If the baud rate to be measured is 9600, then the time of each bit is: 1/9600 ≈ 104 μs. Generally, there are 5 small grids in each large grid horizontally on the oscilloscope. To see one bit clearly, you generally need one. A small grid is enough, then the time base is: 104 μs * 5 = 520 μs, which means the time base needs to be 500 μs.

Note: The coupling mode selected during measurement is DC, the edge type is falling edge, and the level of the measured serial port is TTL level. When the serial port at this level is not transmitting data, the level is high, and the start bit is judged by pulling it low. .

The picture below shows the baud rate of 9600, and the data sent is 0x55:

0x55_9600_.PNG

The oscilloscope used is Hantai's IDSO1070. From the cursor measurement, we can see that the time between AB is 107.422 μs, which is almost the same as the calculated 104 μs.

The picture below shows that the baud rate is 9600 and the data sent is 0x00. Because the data bits are all 0, you can see that it is always low:

IMG_0360.PNG

How to measure serial port baud rate with oscilloscope

Premise: You need to be able to find a bit from the signal.
It is known that the sent data bit is 0x55020000, and the binary digit of 0x55 is 10101010.
As shown in the figure, randomly select a bit and measure it with the cursor. The time is: 1.074us, the frequency is: 930.909kHZ, and the closest baud rate is: 921600, so the baud rate of the measured signal is 926100.

IMG_0361.PNG

refer to:

https://electronics.stackexchange.com/questions/17562/how-to-read-serial-data-from-oscilloscope