EZT-430i Communications Manual
Serial
Communication
CSZ
EZT-430i
REV
C
4.1
4 Serial
Communication
The user communications interface for EZT-430i employs serial communication, which is the exchange of
data in a one-bit-at-a-time, sequential manner on a single data line or channel. Serial contrasts with parallel
communication, which sends several bits of information simultaneously over multiple lines or channels. Not
only is serial data communication simpler than parallel, it is also less costly.
Baud Rate
The baud unit is named after Jean Maurice Emile Baudot, who was an officer in the French Telegraph
Service. He is credited with devising the first uniform-length 5-bit code for characters of the alphabet in the
late 19th century. What baud really refers to is modulation rate or the number of times per second that a line
changes state. This is not always the same as bits per second (BPS). However, if you connect two serial
devices together using direct cables then baud and BPS are in fact the same. Thus, if you are running at
9600 BPS, then the line is also changing states 9600 times per second.
Typical baud rates used for computers are 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 38400, 57600
and 115200 baud. As the baud rate increases, so does the transmission rate of data. Thus you get more
information in a shorter period of time. However, the faster the transmission rate, the more susceptible it is to
error due to the quality of the cable and sources of electrical “noise” in the environment. When operating in
the standard interface mode, EZT-430i uses a 9600 baud rate. When operating in the simulated Watlow
F4S/D mode, EZT-430i uses a 19200 baud rate.
In order for a device to communicate with EZT-430i , it must
have its serial port set for either 9600 baud or 19200 baud based on the selected interface type in order for
data communications to work properly.
Start and Stop Bits
The start bit informs the receiving device that a character is coming, and a stop bit tells it that a character is
complete. The start bit is always a 0. The stop bit is always a 1. The human speech equivalent of these bits
could be a clearing of the throat to get someone’s attention (start bit); and a pause at the end of a phrase
(stop bit). Both help the listener understand the message.
A stop bit has a value of 1 - or a mark state - and it can be detected correctly even if the previous data bit also
had a value of 1. This is accomplished by the stop bit's duration. Stop bits can be 1, 1.5, or 2 bit periods in
length. EZT-430i uses the default – and most common – length of 1 period for the stop bit.
A device used to
communicate with EZT-430i must also have its serial port set to use a stop bit of 1 in order for data
communications to work properly.
Parity Bit
Besides the synchronization provided by the use of start and stop bits, an additional bit called a parity bit may
optionally be transmitted along with the data. A parity bit affords a small amount of error checking, to help
detect data corruption that might occur during transmission. There are several defined parity selections
available for serial communications. They are even parity, odd parity, mark parity, space parity or none at all
can be used.
When even or odd parity is being used, the number of marks (logical 1 bits) in each data byte are counted,
and a single bit is transmitted following the data bits to indicate whether the number of 1 bits just sent is even
or odd. Mark parity means that the parity bit is always set to the mark signal condition and likewise space
parity always sends the parity bit in the space signal condition. Since these two parity options serve no useful
purpose whatsoever, they are almost never used.
When operating in the standard interface mode, EZT-430i offers parity settings of Even, Odd and None.
When operating in the simulated Watlow F4S/D interface mode, the parity is defaulted to “None” and is not
adjustable.
In order for a device to communicate with EZT-430i , it must have its serial port set to use the
same parity setting in order for data communications to work properly.
