Kollmorgen BDS5, Installation And Setup Manual

Page: 48 / 150

C
HAPTER
2 - I
NSTALLATION
BDS5
2-12
2.6.4.8 Wiring C5, Serial
Communications
Connector C5, the Serial Communications Connector,
is on the front of the BDS5. It is a 9-pin, D-type, sub-
miniature plug connector (DE-9P). The
communications cable must have the mating DE-9S
connector. See the System Wiring Diagram (A-93103,
Sheet 3). Note that wiring for RS-232 and RS-485 is
completely different. Refer to the model number to
determine if your unit is RS-232 or RS-485. Be sure
that the common of the BDS5 and the power supply
common of your computer or terminal are electrically
connected to each other, whether you are using
RS-232 or RS-485. Use the COM pin on the serial
connector (Connector C5) for the BDS5 common.
•
RS-232 VS RS-485
The BDS5 can communicate with a terminal or a
computer over a serial data line with EIA RS-232-C,
the most common electrical interface for terminals and
personal computers. It can also communicate with
EIA RS-485, a standard that supports multiple devices
on one serial line. RS-485 is an upgrade of RS-422;
RS-422 is restricted to one transmitter per serial line;
otherwise, the devices will work with RS-485 devices.
You should specify the communication standard that
you want when you order your BDS5.
When choosing between RS-232 and RS-485, there
are a number of factors to take into consideration.
RS-232 is much more common than RS-485. Most
terminals and computer serial ports are RS-232;
however, RS-485 is becoming more available on
personal computers. RS-485 is differential; RS-232 is
single-ended. To illustrate this, RS-232 transmits one
output, TxD. Alternatively, RS-485 simultaneously
transmits TxD+ and TxD-, the logical inverse of
TxD+. (Logical inverse means that if TxD+ = 1, then
TxD- = 0). RS-232 transmitters typically have series-
terminated outputs, while RS-485 transmitters do not.
All this makes RS-485 less susceptible to noise and
able to transmit over much longer distances. On the
other hand, RS-232 is easier to use and much less
susceptible to transmission line effects. RS-232 is also
less expensive. A major advantage of RS-485 is that it
allows multidrop communication, where many axes
can be connected on one serial line.
If you have an RS-232 terminal or computer, and you
want to use RS-485, either for multidrop or for noise
immunity, then you can purchase an RS-232-to-RS-
485 converter. For example, Anaheim Automation
(Anaheim, CA) produces Model DC 2170 for this
purpose.
The RS-232 serial input and outputs connect to 75155
line driver/receivers. The RS-485 serial input and
outputs connect to 75176B line driver/receivers.
These chips are available from many IC
manufacturers, including Texas Instruments.
Table 2.3. Communication Requirements
To Communicate With Your BDS5, You Will Need:
RS-232 Terminal
or
IBM-PC Compatible with Communication
Software
or
RS-485 Terminal
and
Connector for Your Terminal
DE-9S Connector (Provided with BDS5)
3-Wire-with-Shield Cable (RS-232)*
5-Wire-with-Shield Cable (RS-485)*
* Use one of the conductors to connect the power
supply commons. The shield should not be used for
this connection, but should connect to earth ground.
•
LINE TERMINATION
The BDS5 provides line termination for RS-485. An
RS-485 line may need to be terminated to reduce
ringing on long cables. (In this section, Line refers
specifically to the RxD+/RxD- pair or the TxD+/TxD-
pair.)
A line is terminated by connecting a resistor from
RxD+ to RxD- or TxD+ to TxD-. Terminating
resistors are provided inside the BDS5. These
resistors are connected by installing jumpers across
Pins 3 and 4, and across Pins 7 and 8 on J1 on the
front of the BDS5. The lines should only be
terminated at the end of the communication cable.
For example, if you are using several BDS5's in
multidrop, then you should install the jumpers only on
the units at the ends of the serial cable.