Raymarine RayTech RNS 5.0 Getting Started page 27

Installation Guidelines
circuit. While the boat's power ground may, co-incidentally, be at the same level as the
RS-232 signal ground, there is no industry standard that requires this. Since the RS-232
transmit and receive data signals reference a common signal ground to maintain their
integrity, you must connect the signal ground circuit directly between the two RS-232
linked devices.
To wire one RS-232 device to another:
1. Connect device A's Tx lead to device B's Rx lead.
2. Connect device A's Rx lead to device B's Tx lead.
3. Connect device A's signal ground (SGnd) lead to device B's SGnd lead.
RS-232 uses a common ground, which differs in electrical specification form NMEA's
transmit/receive- pair arrangement. Because of these signal level differences, the way
you interconnect an RS-232 device and an NMEA device varies with the application.
You may also encounter voltage differences when interconnecting older RS-232/NMEA
Note:
hardware. Take care to ensure the correct connections.
To wire an RS-232 device to
1. Connect the RS-232 device TX lead to the NMEA device RX+ lead.
2. Connect the RS-232 device SGnd lead to the NMEA device RX- lead.
To wire an RS-232 device to
device:
1. Connect the RS-232 device Tx lead to the NMEA device Rx+ lead.
2. Connect the RS-232 device Rx lead to the NMEA device Tx+ lead.
3. Connect the RS-232 device SGnd lead to the NMEA device Tx-
There are some infrequent cases where binding the NMEA device Tx- and Rx- leads
together may cause difficulties. If you do encounter problems, you will need to use an
RS-232 to NMEA converter between the two devices. A converter is required in rare
cases, but is a good place to begin troubleshooting if problems arise with the RS-232/
NMEA connection. It should be noted that the modern Furuno radar systems do
require a converter.
Circuit grounding issues
The most important issue in electrical connections is proper circuit grounding. In
addition to all of the other electrical gremlins that poor grounding gives rise to,
instrument signals are easily scrambled if they are badly grounded. This results in
erratic and unreliable displays. Installations using both AC and DC current have a
separate ground circuit for each. In such cases, the checklist that follows will ensure
that the ground circuits are kept fully isolated:
• Always use isolating transformers or a separate power-inverter to run PC, monitors
and other sensitive electronic instruments or devices.
provide input
to an NMEA device:
provide and receive input
23
from an NMEA
and
Rx- leads.