The purpose of termination resistors in an NMEA 2000 backbone is:

• A. To increase power
• B. To limit signal reflections from each end of the backbone.
• C. To provide shielding
• D. To minimize impedance mismatches

Answer: (B)

Termination resistors on an NMEA 2000 backbone are used to match the cable’s characteristic impedance and absorb signal energy at the ends of the bus. The backbone uses CAN-style differential signaling with a characteristic impedance around 120 ohms, so placing a 120-ohm terminator at each end makes the line appear as a continuous 120-ohm load rather than an open or mismatched line. When a transmitter drives a bit onto the bus, impedance mismatches at the ends cause reflections that travel back along the line and can interfere with following bits, causing errors and degraded communication. Proper termination dampens these reflections, maintaining signal integrity and enabling reliable data transfer. It doesn’t increase power or provide shielding; its job is to prevent reflections by matching the impedance at the ends of the backbone.