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© 2009 Active Research Limited
RS485 Interfacing
The basics
RS485 interfaces are much like RS422 interfaces, but with
the ability for the connection to be a listener or a talker
depending upon port direction.
The USG-1 transceiver changes direction automatically.
When installed on a PC, the USB driver sets up a virtual
communications port ”VCP” on the host PC. When data is
sent to this port, the USG-1-485 transceiver automatically
becomes a driver and sends data to the RS485 network.
Once all data has been sent, the transceiver automatically
switches back to receive mode.
In addition, an optional link on the USG-1-485 board can
be set to “echo” mode, where data on the bus sent from
the USG-1-485 returns back to the PC. This link is factory
set to “no echo”.
Actisense
produces a full range of products to solve many
marine and other interfacing requirements.
these and other
Actisense
interfacing products (NMEA
Multiplexers, NMEA Buffers, and NMEA Autoswitches) as
well as Depth sounders.
The RS485 signals
RS485 uses a ”differential” signalling scheme, whereby two
wires are used to transmit the data. These connections will
be labelled as either “
A
” and “
B
“ or “
+
” and “
-
“ respectively,
depending on the instrument and manufacturer.
When connecting between different manufacturers, there
can be some confusion, but it is simple and easy to
remember: “
A
” connects to “
+
” and “
B
“ connects to “
-
“.
Opening the USG-1
The USG-1 comes supplied with a factory installed
connection cable with tinned solder wire ends.
Using this
cable means that you will not need to open the USG-1-
485 case to make your connections.
If you need to use your own cable, Phoenix style
connectors are provided within the USG-1-485 to allow
you to connect it. A separate grommet is also provided for
this purpose - simply slide it over your own cable before
connecting it to the Phoenix style connectors.
To open the USG-1-485, remove the two screws in the
base of the USG-1, then slide off the top of the case. The
grommets need to be slid off the top of the case in order to
access the internal connections. You will be left with the
USG-1-485 circuitry attached to the base of the unit and
the two supplied cables attached to their connectors.
Note: When opening the USG-1-485 case, be aware
that the circuitry inside is not 100% protected against
static electricity. Please ensure that, when opening
the case, you use precautions against static damage
- by only touching the connector block and by holding
the unit by its base. In this way, the risks of static
damage will be minimised.
Summary of Contents for USG-1-B-485
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