The baud rate is the speed, or number of signals per second, successive, independent signals can be sent so that they still remain distinguishable. Bytes may be transmitted by providing one physical path for each bit so that an entire character is sent at once, all bits in parallel , or they may be transferred as a sequence of bits on a single, serial connection. Describe Asynchronous and Synchronous data transmission. Asynchronous data transfer Used for low speed data transfer. Is cheaper than Synchronous transfer.
Asynchronous devices transmit characters individually with arbitrary time intervals in between.
To ensure that the receiver is paying attention and ready to handle the bits in the data character, a start bit is sent first, followed by the data bits, and finally one or more stop bits. At low speeds, these ten or eleven bits are relatively easy for the receiver to handle, because the slight variations in clocking between the transmitter and receiver will be small compared to the length of each bit signal, and should not add up to a problem even over the total length of the character. Synchronous data transfer Used when higher data rates are desirable or when a large number of characters need to be transferred consecutively. The beginning of transfer becomes even more important, because the receiver must be able to ensure that its clock will stay synchronised with the transmitter over the duration of the entire group of character. Special bit sequences called flags, which amount to the same functionality as asynchronous start and stop bits, are placed at the beginning and end of the group rather than before and after each character.