- Automatic Data Direction Control
Under RS-485 2 wire communication, one thing very important
is to determine when to switch on/off the transmitter due
to the restriction of RS-485. As there's only 1 node can switch
on it's transmitter on the RS-485 2 wire bus at the same time,
the node wish to send data must switch on it's transmitter
then switch it off after last bit sent out.
There are 2 approaches to do the job. One is to use RTS signal
to control transmitter manually by software. The other is
Automatic Data Direction Control.
Automatic Data Direction Control switch on/off transmitter
precisely by hardware. It effectively simplifies the complexity
of timing control for software.
- ASIC (Application Specific Integrated Circuit)
ASIC chip is a special designed chip for providing unique
functions. It can replace general-purpose commercial logic
chips and integrate several functions or logic control blocks
into one single chip in order to lower manufacture cost and
simplifies circuit board design.
- Asynchronous communication
Digital communication (as between computers) in which there
is no timing requirement for transmission and in which the
start of each character is individually signaled by the transmitting
device.
- Baud rate
Baud rate means transmission speed (Unit: bits per second,
bps ), especially for RS-232/422/485 interfaces.
- CompactPCI
CompactPCI is a very high performance industrial bus based
on the standard PCI electrical specification in rugged 3U
or 6U Eurocard packaging. Unlike its desktop cousin, the 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 I/O can break
out either to the front or through the rear. For more information,
please refer to http://www.picmg.com.
- DTE
DTE is acronym for Data Terminal Equipment defined in RS-232
specification. Examples of DTE are computers, printers & terminals.
- DCE
DCE is acronym for Data Communication Equipment defined
in RS-232 specification. The function DCE is to convert data
from one interface, say digital signal, to another interface,
say analog signal. Example of DCE is modem.
- FIFO (First In First Out)
FIFO is a concept to describe the behavior of the buffer.
It means the character received first will be sent out in
first priority. FIFO buffer is used to reduce the frequency
of interrupt process for UART chips, such as C16550C, in serial
communication.
- Flow Control
When processing capability between 2 devices are dramatically
different, say dot matrix serial printer and RS-232, Flow
Control is necessary to regulate data flow to ensure the communicate.
There are basically 2 approaches to do flow control for RS-232
communication.
- Software approach : XON/XOFF
XON(0x11) and XOFF(0x13) are defined as special control
code during communication. These 2 codes will be transmitted
together with data characters.
When either of the devices receives XOFF, it stops transmitting
data until XON receives. The deficiency for this approach
is that the data must not contain these 2 codes.
- Hardware approach: RTS/CTS
RTS(Request To Send) and CTS(Clear To Send) are 2 signals
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 deficiency for this approach is that
it needs 2 more wires but provide the capability to send
binary data.
- Intelligent multiport board
Intelligent multiport board has on-board processing capability
to cope with huge amount of data and therefore shares host
processor workload. The on- board processor acts as a Front
End I/O processor to handle necessary data processing before
it sends to the host processor. And on-board memory provides
large buffer eliminates the chance to lost data during data
transmission.
- Non- intelligent multiport board
Non-intelligent multiport board equipped with UART chips
and necessary peripheral Ics. All the data transmit/receive
processing is done by motherboard CPU. It creates a lot of
CPU workload and therefore can only be used within limited
ports. However, Non-intelligent multiport board is a economic
and robust solution in small scale application.
- Optical Isolation
Communication devices may be damaged by inequality of ground
voltage level when transmission line is long. Optical isolator
is adopted to prevent from such damage and is able to transmit
data at the same time.
- Parallel
The concept of "parallel" represents a connection in a computer
system in which the bits of a byte are transmitted over separate
channels at the same time.
- RS-232
RS-232 is a serial communication standard providing asynchronous
communication capabilities with hardware flow control, software
flow control, and parity check. It is widely used for decades.
Almost all gears, instruments with digital control interface
or communication devices equipped with RS-232 interface. The
typical transmission speed of RS-232 is 15 meters/9600bps.
- RS-422
RS-422 provide much longer transmission distance but less
signal line compares to RS-232. RS-422 adopts differential
transmission technology and thus provides high-speed transmission
up to 10Mbps and maximum transmission distance up to 1.2km/110kbps.
- RS-485
RS-485 is an enhanced version of RS-422. It is compatible
to RS-422 interface and provides 2 wire bus topology. By using
RS-485 2 wire bus, you may establish a most economic network
system. However, RS-485 only defines electronic signal specifications,
users must define software protocol for 2 wire communication
by themself.
- Serial
The concept of "serial" represents a connection in a computer
system in which the bits of a byte are transmitted sequentially
over a single wire.
- Surge Protection
TOV(Transient Over Voltages) which comes from lightning,
electrostatic discharges and other forms of high voltage is
one of the major cause for equipment damage. Surge protector
absorbs TOV and effectively protects your equipment.
- Synchronous communication
Digital communication (as between computers) in which a common
timing signal is established that dictates when individual
bits can be transmitted, in which characters are not individually
delimited, and which allows for very high rates of data transfer.
- TCP/IP (Transmission Control Protocol/Internet
Protocol)
TCP/IP is a set of protocols developed to allow cooperating
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 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
or IP/TCP 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 will contribute 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 means transmission performance that means actually
transmitted or received characters during certain period of
time. Figure of throughput depends on CPU, Memory, performance
between 2 devices, pattern of measurement, as well as performance
of the operating system. It's usually measured in BPS (Byte
Per Second).
- UART (Universal Asynchronous Receiver-
Transmitter)
UART controls the data transmission and receive of serial
communication devices in a computer. The UART chip converts
digital data between parallel data inside of PC and serial
data from RS-232/RS-422/RS-485 line driver.
