Appendix E - Synchronous and Asynchronous Communications
Sealevel Systems
ACB-II
Page
18
Synchronous Communications
Synchronous communications is used for applications that require higher
data rates and greater error checking procedures. Character synchronization
and bit duration are handled differently than asynchronous
communications. Bit duration in synchronous communications is not
necessarily pre-defined at both the transmitting and receiving ends.
Typically, in addition to the data signal, a clock signal is provided. This
clock signal will mark the beginning of a bit cell on a pre-defined
transmission. The source of the clock is predetermined and sometimes
multiple clock signals are available. For example, if two nodes want to
establish synchronous communications, point A could supply a clock to
point B that would define all bit boundaries that A transmitted to B. Point
B could also supply a clock to point A that would correspond to the data
that A received from B. This example demonstrates how communications
could take place between two nodes at completely different data rates.
Character synchronization with synchronous communications is also very
different than the asynchronous method of using start and stop bits to
define the beginning and end of a character. When using synchronous
communications a pre-defined character or sequence of characters is used
to let the receiving end know when to start character assembly.
Figure 7 - Synchronous Communications Bit Diagram
