Asynchronous vs. Synchronous Transmission
When asynchronous transmission is selected, each byte is surrounded by control bits. One extra bit is added at the front of the character and another one or two bits are added at the end.
The front bit is called a start bit and the bit at the end is called a stop bit. There is also the error checking or parity bit.
Synchronous transmission is when blocks of bytes are wrapped in start and stop bytes, called synch bytes.