Control Techniques UD70, User Manual

Page: 61 / 154

UD70
Issue code: 70nu2
Serial communications 6-1
6 Serial Communications
6.1 Introduction
A serial communications link enables one or more
UD70
cards to be used in
systems controlled by a host unit such as a
PLC
or computer. The
communications link uses the
RS485
standard.
The
UD70
may also act as the host in a system, controlling Drives,
UD70
modules,
MD29
cards or other devices fitted with a suitable interface.
The host controller can operate up to thirty-two
EIA RS485
devices with the
use of line repeaters. Each transmitter and receiver of Control Techniques
devices loads the line by two unit-loads. Therefore in two-wire mode, each
Control Techniques device loads the line by four unit-loads. This means that
no more than a total of seven such devices can be connected in a single
group, allowing up to four unit-loads for the line repeater. Up to 15 devices
can be connected if four-wire mode is used.
When line repeaters are used, up to 81 Control Techniques devices can be
operated. In this case the devices are organized in up to nine groups of nine.
A particular group or groups can be given commands without affecting
other devices or groups of devices.
Group 1
Group 2
Host controller
RS485 mulitdrop link having two groups of four units RS485 mulitdrop link having two groups of four units
The communications port of the
UD70
is the male D-type connector on the
right side of the board. The
UD70
may be used in either 4-wire or 2-wire
mode. The
RS485
port is fully opto-isolated.
RS422
is also supported.
Caution
An RS232
connection may be made to the
RS485
port, but is not
recommended due to its inferior specification (noise
rejection, limited maximum cable length, etc).
RS232
is not
the same as two-wire
RS485
.