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EmpirBus NXT SP-12 User manual Ver 1.23
4.3 Terminal resistor switches
The SP-12 has onboard terminal resistors that can be connected to the bus using switches located
beneath button 5 on a horizontal panel and under button 8 on a vertical panel. See figure 4.1, 5.1
and 5.2 for position of the switch.
The switch is on as it is pushed towards on, and off as it is pushed towards the numbers. Switch 1 and
2 will individually add 120 Ω to the CAN bus Switch 3 will add 1 kΩ to the LIN bus.
The NMEA2000 requires a total resistance of the bus of 60Ω which is achieved by two parallel 120
resistors. If the SP-12 panel is placed within 6 meters from the end of the bus, an internal terminal
resistor in the SP-12 can be used to exclude one external terminal resistor.
If the total bus length is shorter than 6 meters, both external terminal resistors can be excluded by
using both of the internal terminal resistors in the SP-12.
ON
.
1 2 3
.
Figure 4.2: Internal terminal resistor switches
Figure 4.4: Bus example with total bus length less than 6 meter
Bu
s p
ow
er
feed
SP-12 with terminal
resistor switch 1
and 2 switched on
DCM-11
MCU-11
