User`s manual

Watlow Controls Communications Guide 25
Formerly referred to as RS-
(Recommended Standard). (See EIA-232,
EIA-422, EIA-423 and EIA-485)
Electronic Industries Association
(EIA)
An association in the US that establishes
standards for electronics and data
communications
Encode
To embed information into a piece of
data. This is the reverse of decode. Ex.
Let’s let 01000001 stand for an “A”.
Error Correction
When an inconsistency is in the data, a
method is used to detect and/or return the
data to its correct value. This can be done
through several methods, parity, checksum
and CRC (cyclic redundancy checksum) are
a three of these.
Ethernet
A local area network developed by Xerox
in the early 70’s and standardized by
Xerox, Digital Equipment and Intel in
1978. This is a serial communications
method which all devices share the lines.
An address is sent in a packet to talk to a
device on the line. This protocol supports
peer-to-peer communications.
Even
This term is used with parity. See parity.
Fieldbus
The term fieldbus is a general definition
for an industrial network media that
resides at the machine level and below in a
total network system. The primary
purpose of this network is to interconnect
the machine level and sublevel control
functions and services in a distributive
topology. It is not a particular protocol or
physical connection system. Included in
this generalization definition are standard
protocols of Profibus, Modbus, DeviceNet,
SDS, WorldPIP, and P-Net.
Firmware
Instruction or data stored in an IC
(integrated circuit) or on a read only disk.
This data is programmed once and cannot
easily be changed as software can.
Full
See Full Duplex.
Full Duplex
Full is used to mean the duplex’s full
capability. The ability to send and receive
data at the same time. The same as duplex.
GPIB
See IEEE488
Half Duplex
The ability to send or receive data, but not
at the same time. “To listen or talk, but
not both at the same time.”
Handshake (Handshaking)
Exchange of predetermined signals
between two devices establishing a
connection. Using extra wires or software
signals to coordinate communications,
signals can be sent to tell the transmitter
the current status of the other device
receiver. Ex. Are you busy or are you
ready?
Hex or Hexadecimal
Number based system where sixteen
characters exist, 0 to 9, A to F. Counting
is 0..9,A,B,C..
HMI
Human to Machine Interface typically
performed in software on a personal
computer. Also called MMI.
IEEE488
Bus developed by Hewlett-Packard in 1965
as HP-IB. Also referred to as GPIB
(General Purpose Interface Bus). Consist
of 8 data lines and 8 control lines. Bus
length limited to 20.0 meters. Supports 15
devices on the bus at one time.
Logic Level
A voltage measurement system where only
two stable voltage values exist. Ex. 0v and
5V, or -3v and +3v.