Furuno FA-100 - Manual (Page 25)

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3.7 Jumper Setting in the Junction Box
Each RS-422 RX line (on the PCB 24P0031 in the junction box) has a jumper block
with 240 ohms termination resistor. The junction box is shipped with all jumper
blocks connected between the #3 and #4 terminals pins, terminating RX lines with
240 ohms. Assuming that an external equipment has the output voltage of ±5 V,
more than 21 mA of output current is required.
If multiple equipment are connected to an output port of an external equipment,
change to jumper block setting to between the #1 and #2 pins to reduce the load on
the FA-100. Then, the input impedance of the RS-422 RX lines in the FA-100
becomes more than 2.4 k ohms.
We recommend that you leave the connection of the jumper block between #3 and
#4 pins if only the FA-100 is connected to an external equipment.
1
2
3
4
Jumper block (6 pcs)
Factory setting: #3-#4