I am new to embedded programming and have very little knowledge in how digital/electronic system works, but I have been given a task to bring up USART communication between two chips. For that, I have started learning from the basics of serial communication etc etc. What I don't understand in serial protocol is that what is the difference between synchronous and asynchronous communication? Let us say I have two devices d1 and d2. They both are aware of their baud rates. d1 sends data at a baudrate of 9600 and d2 receives data at the same rate. Then my question is, how the clock plays role in synchronous communication? Means with baud-rate I think we have all the information of the communication channel. With this confusion I am not able to clearly understand the exact difference between synchronous and a synchronous communication.
Electronic – What difference does the clock make in synchronous vs asynchronous communication
baudrateclockspisynchronous
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Best Answer
With asynchronous data transmission, when there is no payload data to be sent, the data line becomes idle and therefore the receiver waits for a transition that marks the beginning of new incoming data. In this respect there is no definite phase relationship between data previously received and the new data arriving.
This is why it is called "asynchronous"
With synchronous data, either a clock is permanently present as a seperate signal or, the clock is embedded into the data (as per Manchester encoding or scrambling) so that the receiver is always aware when real payload data could be present. When no payload data is present the clock is still present. Manchester encoded data: -
Whether you extract the clock from the data (or have a dedicated clock line) you need a clock; that is fundamental to any data transmission. Asynchronous transmission re-creates a clock internally based on the agreed baud rate and the first transition of data following an idle period. From this point on until the end of the data block it generates a clock internally for the whole transmission.
So the clock plays a vital role in both asynchronous and synchronous data communications.
Not quite - knowing baud rate at both ends is useful but it doesn't tell you when bits actually change state in the data - this "synchronization" to the data is performed by the idle-to-start bit transmission in asynchronous data and is everpresent in synchronous data communication.