User`s manual

Watlow Controls Communications Guide 23
Appendix
Glossary
Address
A unique designator for a location of data
or a controller that allows each location or
controller on a single communications bus
to respond to its own message. Similar to
your own residence address.
ANSI
A merican N ational S tandards I nstitute
ANSI x3.28
The American National Standards Institute
developed this communication standard
protocol. This method uses a unique
address for each device. Only the master
can initiate a communications session by
sending an address and then the <ENQ>
character. All other messages must start
with a start of text <STX> and end with an
end of text <ETX> character. The bus is
released to the other device by sending
<EOT> character. Messages are <ACK>
acknowledged or <NAK> negative
acknowledged.
ASCII (pronounced AS-KEY)
American Standard Code for Information
Interchange. A universal standard for
encoding alphanumeric characters into 7
or 8 binary bits.
Asynchronous
Communications where characters can be
transmitted at an unsynchronized point in
time. In other words, it can start and stop
anytime. The time between transmitted
characters may be of varying lengths.
Communication is controlled by “start”
and “stop” bits at the beginning and end of
each character.
Baud
Unit of signaling speed derived from the number
of events per second (normally bits per second).
Baud rate
The rate of information transfer in serial
communications, measured in bits per second.
Binary
Number based system where only two characters
exist, 0 and 1. Counting is 0, 1, 10, 11...
Bit
Derived from “ BI nary Digi T ”, a one or zero
condition in the binary system.
Byte
A term referring to eight associated bits of
information, sometimes called a “character”.
CAN Bus
The C ontroller A rea N etwork Bus is a serial
communications protocol that includes software
and hardware. CAN was originally developed by
the German company Robert Bosch for use in the
auto industry to provide a cost-effective
communications bus for in-car electronics.
Character
Letter, numeral, punctuation, control figure or
any other symbol contained in a message.
Typically this is encoded in one byte.
Communications
The use of digital computer messages to link
components. (See serial communications and
baud rate)
Converter
This device will convert from one hardware
interface to another such as from EIA-232 to EIA-
485. The converter may be transparent to the
software, which means you do not have to give
any special considerations to software
programming.
CRC
When data is corrupted during transmission, a
method is used to return the data to its correct
value. This can be accomplished through several
methods: parity, checksum and CRC (cyclic
redundancy checksum) are three of these. C yclic
R edundancy C hecksum is an error-checking
mechanism using a polynomial algorithm based
on the content of a message frame at the
transmitter and included in a field appended to
the frame. At the receiver, it is then compared
with the results of the calculation that is
performed by the receiver.