data transmission from an originating source that is not synchronized to any clock pulse or external common event
NOTE 1 The data frame is delimited with (e.g.) start and stop signals. Both communication terminals do not need to have local clocks synchronized.
NOTE 2 Data transmission systems that foresee asynchronous data transfer can allow senders to attempt to transfer data at any time. If two or more senders send data at the same time then there is a conflict and an arbitration scheme is used to determine the order in which the senders can put their data on the bus. Priority is then used to differentiate between information to be delivered urgently, and data whose delivery is less time critical. When there is a conflict between two or more senders the one with highest priority is allowed to send its data first.