What Is "Recessive - Maretron N2KMeter User Manual

13.2 What is "recessive?"

messages consist of 1's and 0's. The recessive state of the bus (where the
®
NMEA 2000
differential voltage between NET-H and NET-L is close to zero) represents the logical value 1
(opposite from what you might expect). The bus is always in the recessive state except when a
node is transmitting.
The N2KMeter measures the difference between NET-H and NET-L for recessive bits on the
network, and if the difference is not close to 0 volts, N2KMeter indicates a fault.
For NET-H/L differential recessive voltage levels we suggest:
 Check for shorts and opens on the NET-H and NET-L wires
 Check for a missing or bad terminator (should be two 120 ohm terminators from NET-H
to NET-L - one at each end of the network)
 Disconnect nodes one at a time or temporarily split the network to check for faulty
transceivers or cables.
Page 20
NET-H/L Diff. V deals with
these two wires (NET-L
(blue) & NET-H (white))
Revision 1.3