Asynchronous transmission
Asynchronous transmission is data transmission without a clock signal, and instead we send extra signals to indicate when data is being sent.
For example, we might send a start bit to indicate that we’re about to send data, and then we send the data bits, and then we send a stop bit to indicate that we’re done sending data.
The advantage of asynchronous transmission is that the sender and receiver don’t need to be synchronised to the same clock signal, and they don’t need to always be listening to a clock signal, which can save power.
The disadvantage is that it can be slower than synchronous transmission, because there’s overhead of sending extra signals like start and stop bits, and the sender and receiver need to wait for each other to be ready before sending data.
Start and stop bits
We send a start bit when we’re about to send data, to indicate to the receiver that data is coming.
Then, after we send the data bits, we send a stop bit to indicate that we’re done sending data.
The start signal may be a 0 or a 1 depending on the protocol. The key thing is that it is different from the stop bit.
Synchronisation
In asynchronous transmission, the sender and receiver are not synchronised to the same clock signal, so they need to use the start and stop bits to indicate when data is being sent. They are synchronised to each other, after the start bit. So they know when to read the next bit, but they don’t have to stay constantly synchronised to a clock signal, which can save power.
Examples of asynchronous transmission
- UART (Universal Asynchronous Receiver Transmitter)
- RS-232 (a standard for serial communication)
- MIDI (Musical Instrument Digital Interface)
flashcards
| Question | Answer |
|---|---|
| What is asynchronous transmission? | A method of data transmission without a shared clock signal, using extra signals like start and stop bits. |
| What is the main purpose of sending extra signals like start and stop bits in asynchronous transmission? | To indicate when data is being sent and when it is finished, without relying on a clock signal. |
| What is a key advantage of asynchronous transmission? | The sender and receiver don’t need to be synchronised to the same clock signal, which can save power. |
| What are examples of protocols that use asynchronous transmission? | UART (Universal Asynchronous Receiver Transmitter), RS-232 (a standard for serial communication), MIDI (Musical Instrument Digital Interface) |
| Why can asynchronous transmission be slower than synchronous transmission? | Because of the overhead of sending extra signals like start and stop bits, and the need to wait for each other to be ready. |
| What does a start bit do? | It is sent to indicate to the receiver that data is coming. |
| What does a stop bit do? | It is sent after the data bits to indicate that data transmission is done. |
| How is the start signal defined in relation to the stop signal? | The start signal must be different from the stop bit. |
| How are the sender and receiver synchronised in asynchronous transmission? | They are synchronised to each other after the start bit, allowing them to know when to read the next bit. |
| What power-saving feature is enabled by asynchronous transmission? | The sender and receiver do not need to stay constantly synchronised to a clock signal. |
| Define a start bit. | A signal sent before data bits to indicate data is about to be sent. |
| Define a stop bit. | A signal sent after data bits to indicate data transmission is complete. |