The serial connection for the NMEA message follows the RS232 standard. The interface is capable of handling voltages
between ±15 VDC.
Low voltages are marks and represent a logical 1.
High voltages are spaces and represent a logical 0.
The serial line idle state (MARK) is a low voltage indicating a logical 1. When the start bit is asserted, the positive voltage will
be asserted representing a logical 0. As an example, the transmission of an ASCII "$" character is shown in
Figure 7-5
below
.
Figure 7-5 RS-232 Example Transmission
Chapter 7 • Sensor Inputs
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