1.1.11 Serial Interfaces
This chapter provides extra information about the serial interfaces used in the Marine Electronics.
• IEC 61162-1
This standard is the most commonly used. In the standard, the sender (Tx side) and receiver (Rx side) are referred to
as talker and listener.
It has the following characteristics:
• Communication speed: baud rate of 4800, 8 databits, 1 stop bit, no parity.
• One talker (Tx side, commonly a sensor such as GPS) may be connected to one or more listeners (Rx side, e.g.
displays or computer systems such as ECDIS). The circuit looks as shown in Figure 7: IEC 61162-1 Circuits on
page 15.
Figure 7: IEC 61162-1 Circuits
There are some requirements to the wiring of the signal.
• Tx+ and Tx– are connected to Rx+ and Rx– respectively.
• On the transmitting side the shield of the cable is connected to earth , and is NOT connected on the listener side.
Note In case the NMEA signal is connected both ways, two cables should be used with proper shielding
as described above. (It is just above situation times two for the opposite direction).
Only one talker is connected to the bus, and multiple listeners may be connected to the same bus without the need
for a signal isolator/multiplier. However, it is not forbidden and good practice to use a multiplier since it eliminates
possible faults caused by short circuiting of the signal by a faulty listener. Alphatron is able to supply such a multiplier
if needed (NMEA Distribution Interface Mk.2).
• IEC-61162-2
This standard is applied to provide better characteristics when the data transmission speed is higher.
It has the following characteristics:
• Communication speed: baud rate of 38400, 8 databits, 1 stop bit, no parity.
• One talker (Tx side, commonly a sensor such as GPS) may be connected to one or more listeners (Rx side, e.g.
displays or computer systems such as ECDIS). The circuit looks as shown in Figure 8: IEC 61162-2 Circuits on
page 16.
15 | Installation Instructions
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