B&B Electronics ZXT9-MB2A-KIT - Manual - Manual (Page 25)

Document Number: ZXTxRM-5110m
Page
25
4.1.5 RS-422/485 Four Wire Connections
Figure 4-5 RS-422 / 485 4-Wire Wiring
4.1.6 Termination and Biasing
The radio modem has built in 1.2 kΩ pull-up and pull-down resistors R17 and R14). There
is also a built in 120 Ω termination resistor (R21). These resistors are located on the PCB
behind the cover. Termination is switchable using DIP Switch Position 3. To enable the
termination, set switch 3 to ON “Termination IN”. To disable the termination, set switch 3
to OFF “Termination OUT”.
It is possible to use different value resistors by removing the surface mount components
and placing through-hole resistors (R16, R13, and R19) in the space provided. The
surface mount components are located directly opposite of the through-hole pads that are
visible.
Figure 4-6 Through-hole Resistor Pads