The tail is expanded to include a check code, inserted by the transmitter, and used by the receiver to determine if the data block of characters was received without errors. In this way, synchronous transmission overcomes the two main deficiencies of the asynchronous method, that of inefficiency and lack of error detection. Asynchronous communication data structure Asynchronous systems send data bytes between the sender and receiver. Each data byte is preceded with a start bit, and suffixed with a stop bit or bits. These extra bits serve to synchronize the receiver with the sender.
Synchronization is achieved for each character only.
Asynchronous protocols are suited for low speed data communications. BITS - 1, 1.5, or 2 stop bits. A control code can be generated from a keyboard by holding down the Ctrl key and pressing another key. Data cannot be transferred unless the appropriate flow control line are first asserted. The following is a list of common EIA RS-232 Hardware Handshaking signals.