Appendix E - Synchronous and Asynchronous Communications
Sealevel Systems
ACB-II
Page
17
1
1.5
2
Stop Bits
Parity
Bit
5 to 8 Data Bits
Odd
Even
or
Unused
Remain Idle
or
Next Start Bit
1
0
Idle State
of
Line
Figure 6 - Asynchronous Communications Bit Diagram
This special bit is called the parity bit. Parity is a simple method of
determining if a data bit has been lost or corrupted during transmission.
There are several methods for implementing a parity check to guard against
data corruption. Common methods are called (E)ven Parity or (O)dd Parity.
Sometimes parity is not used to detect errors on the data stream. This is
referred to as (N)o parity. Because each bit in asynchronous
communications is sent consecutively, it is easy to generalize asynchronous
communications by stating that each character is wrapped (framed) by pre-
defined bits to mark the beginning and end of the serial transmission of the
character. The data rate and communication parameters for asynchronous
communications have to be the same at both the transmitting and receiving
ends. The communication parameters are baud rate, parity, number of data
bits per character, and stop bits (i.e. 9600,N,8,1).
