- ADDC (Automatic Data Direction Control)
When using RS-485 2-wire communication, one of the most important
things to determine is when to switch the transmitter on and off.
Because of the restrictions imposed by the RS-485 interface, only 1
node (on an RS-485 2-wire bus) can switch on it's transmitter at any
given time. The node that wishes to send data must switch on it's
transmitter, and then switch it off after the last data bit has been
sent.
There are 2 ways to take care of the job of switching a
transmitter on and off. One method is to use the RTS signal to
control the transmitter manually by software. The other method is to
use ADDC™ (Automatic Data Direction Control).
ADDC switches the transmitter on and off very precisely by
hardware, effectively simplifying the complexity of timing control
by software.
- ASIC (Application Specific Integrated Circuit)
ASIC chips are specially designed chips that provide unique
functions. ASIC chips can replace general-purpose commercial logic
chips, and integrate several functions or logic control blocks into
one single chip, lowering manufacturing cost and simplifying circuit
board design.
- Asynchronous communication
Asynchronous communication refers to digital communication (such
as between computers) in which there is no timing requirement for
transmission, and in which the start of each individual character is
signaled by the transmitting device.
- Baud rate
Baud rate is related to transmission speed. As far as
RS-232/422/485 interfaces are concerned, baud rate is measured in
bps (bits per second).
- CompactPCI
CompactPCI is a very high performance industrial bus based on the
standard PCI electrical specification in rugged 3U or 6U Eurocard
packaging. Contrary to its desktop cousin, a CompactPCI board uses a
high quality 2 mm metric pin and socket connector that meets IEC and
Bellcore standards. CompactPCI boards are inserted from the front of
the chassis, and the I/O can break out either to the front or
through the rear. For more information, refer to
http://www.picmg.com.
- DTE (Data Terminal Equipment)
DTE stands for Data Terminal Equipment, as defined by the RS-232
specification. Examples of DTE are computers, printers, and
terminals.
- DCE (Data Communication Equipment)
DCE stands for Data Communication Equipment, as defined by the
RS-232 specification. The basic function of a DCE is to convert data
from one interface, such as a digital signal, to another interface,
such as an analog signal. One example of DCE is a modem.
- FIFO (First In First Out)
FIFO is a term that describes the behavior of some buffers. FIFO
buffers send out characters in the order that they are received.
FIFO buffers are used to reduce the frequency of interrupt processes
for UART chips, such as the C16550C, used in serial communications.
- Flow Control
Flow Control is necessary to regulate data flow between 2 devices
with dramatically different data transmission speeds (such as a dot
matrix serial printer and an RS-232 interface connection). Flow
Control is needed to regulate data flow, to ensure that the two
devices can communicate with minimal loss of data.
RS-232 communication uses one of two basic approaches to enforce
Flow Control.
- Software approach: XON/XOFF
XON (0x11) and XOFF (0x13) are defined as special control codes
for use during communication. The 2 codes are transmitted along
with data characters. The operating scheme is straightforward:
When either of the devices receives XOFF, it stops transmitting
data until XON is received. The problem with this approach is that
the data itself cannot contain these 2 codes.
- Hardware approach: RTS/CTS
RTS (Request To Send) and CTS (Clear To Send) are separate
signals, sent on separate wires, used for hardware Flow Control.
RTS is an output signal that enables/disables data transmission
for the other device. CTS is an input signal allowing the other
device to enable/disable data transmission. The drawback to this
approach is that 2 more wires are needed, but it also provides the
capability to send binary data.
- Intelligent multiport board
An intelligent multiport board has on-board processing capability
that allows it to cope with huge amounts of data, and in this way
share the workload of the host processor. The on-board processor
acts as a Front End I/O processor to handle the necessary data
processing before it sends data to the host processor, and on-board
memory provides a large buffer that eliminates the chance of losing
data during data transmission.
- Non-intelligent multiport board
A non-intelligent multiport board is equipped with UART chips and
the necessary peripheral ICs. All the data transmit/receive
processing is done by the motherboard CPU. This creates a high
workload for the CPU, and consequentlye can only be used for limited
ports. However, non-intelligent multiport boards are an economical
and robust solution for small scale applications.
- Optical Isolation
Communications devices connected by long cables may be damaged by
the mismatch between ground voltage levels at the two ends of the
wire. Optical isolation uses photo cells at both ends of the line to
isolate the devices' sensitive components from this type of
electrical damage.
- Parallel communication
Parallel communication refers to when data is tranmitted
byte-by-byte. I.e., all bits of one or more bytes are transmitted
simultaneously over separate wires.
- RS-232
RS-232 is a serial communications standard that provides
asynchronous communication capabilities, such as hardware flow
control, software flow control, and parity check. It has been widely
used for decades. Almost all gears, instruments with digital control
interface, and communications devices are equipped with the RS-232
interface. The typical transmission speed of an RS-232 connection is
9600 bps over a maximum distance of 15 meters.
- RS-422
RS-422 is a serial communications standard that provides a much
longer transmission distance, but fewer signal lines compared to
RS-232. RS-422 uses differential transmission technology, and thus
provides high-speed transmission of up to 10 Mbps. The maximum
transmission distance is 1.2 km at a transmission speed of 9600 bps.
- RS-485
RS-485 is an enhanced version of RS-422. It uses a 2-wire bus
topology, and is compatible with the RS-422 interface. By using an
RS-485 2-wire bus, you can establish a very economical network.
However, RS-485 only defines electrical signal specifications; users
must define the software protocol themselves.
- Serial communication
Serial communication refers to when data is transmitted
bit-by-bit, or sequentially, over a single wire.
- Surge Protection
TOV (Transient Over Voltages), which come from lightning,
electrostatic discharges, and other forms of high voltage, is one of
the major causes of equipment damage. A surge protector absorbs TOV
to effectively protect your equipment.
- Synchronous communication
Synchronous communication refers to digital communication (such
as between computers) in which a common timing signal is established
that dictates when individual bits can be transmitted. In this case,
individual characters are not delimited, allowing for very high
rates of data transfer.
- TCP/IP (Transmission Control Protocol/Internet Protocol)
TCP/IP is a set of protocols developed to allow computers to
share resources across a network. It was developed by a community of
researchers centered around the ARPAnet. The most accurate name for
the set of protocols we are describing is the "Internet protocol
suite". TCP and IP are just two of the protocols in this suite.
Because TCP and IP are the best known of the protocols, it has
become common to use the term TCP/IP to refer to the whole family.
Note that these computer services can all be provided within the
framework of TCP/IP.
- Termination Resistors
When an electrical signal travels through two different
resistance junctions in a transmission line, the impedance mismatch
will sometimes cause signal reflection. Signal reflection causes
signal distortion, which in turn contributes to communication
errors. The solution to this problem is to establish the same
impedance at the line ends as in the line itself by terminating them
with resistors. It is normally sufficient when the value of the
termination resistor equals the characteristic impedance of the
transmission line. The resistors should be added near the receiving
side.
- Throughput
Throughput refers to the performance of data transmission, and is
measured by characters actually transmitted or received during a
certain period of time. The throughput of a connection depends on
CPU, memory, performance between the two devices, pattern of
measurement, as well as the performance of the operating system.
Throughput is usually measured in bps (bits per second).
- UART (Universal Asynchronous Receiver-Transmitter)
UART chips control the data transmission and reception of a
computer's serial communications devices. The UART chip converts
digital data between parallel data inside the PC and serial data
from an RS-232/422/485 line driver
