Connecting
♦
Connect IA100 to PC
via RS232 serial port.
Note that not all
RS232 signals
should be used to create
a connection between
the adapter and the PC.
♦
The RS232 part
is powered through
the communication port.
Therefore, adherence
to the data transmitting /
receiving protocol
as illustrated on the left
is crucial.
♦
Since, during transmission,
RxD signal state
is undefined,
we recommend you
to clear the receiving buffer
after each transmission.
♦
On the other hand, connect
the interface adapter
to the control device
network, according
to the RS485 specification
(see '
Networking
').
The two IA100 interfaces
are optically isolated.
Declaration of Conformity
The undersigned hereby declares,
on behalf of COMECO Inc.,
that this device has been manufactured
in compliance with standards
EN 61000 and EN 61010,
and meets the requirements
of Directives 73/23/EEC and 89/336/EEC.
Vladimir Sakaliyski
CEO
COMECO Inc.
Waste Disposal
Do not dispose of
electronic devices
together with
household waste
material!
If disposed of within European Union,
this product should be treated
and recycled in accordance with the laws
of your jurisdiction implementing
the WEEE Directive 2002/96
on the Waste Electrical and Electronic
Equipment.
Networking
Termination
♦
Termination is used to match
the impedance of a node
to the impedance of the transmission
line being used. When impedances
are mismatched, the transmitted
signal is not completely absorbed
by the load and a portion of it
is reflected back into
the transmission line.
If the source, transmission line,
and load impedance are equal,
these reflections are eliminated.
♦
Termination increases load
on the drivers and the installation
complexity, changes biasing
requirements, and makes
system modification more difficult.
♦
The decision whether or not to use
termination should be based
on the cable length and data rate
used by the system.
A good rule of thumb is that if
the propagation delay of the data line
is much less than one bit width,
termination is not needed.
♦
There are several methods
for terminating data lines.
The method we recommend
is adding a resistor in parallel
with the receiver's A and B lines,
only at the extreme ends of data line.
The resistors' value should be equal
to the characteristic impedance
of the line (120
Ω
is a common value).
A termination resistor of less
than 90
Ω
should not be used.
♦
Another type of termination
is through addition of a small capacitor
in series with the termination resistor.
Although this method eliminates
DC loading, capacitor selection
is highly dependent on system
properties.
