Rs-485 Internal Circuit Diagram - Campbell SDM-SIO1A Instruction Manual

3.3.4 RS-485 internal circuit diagram

TX
RX
0V
* Note the external termination resistors are optional. Some applications can use much higher
value resistors and some may not need resistors at all depending on the distance and wire quality
involved.
If the termination resistor is primarily needed for impedance matching then a value matching the
line resistance will have to be used.
`RG' is for connecting the screen/ground of the data lines when in RS485 mode,
there's a 1W 100Ω resistor in series designed to limit any currents that may be
induced due to a difference in ground potentials between the sensor and the SDM-
SIO1.
Internal
External
22R
22R
22R
22R
100R
User Guide
RTS/TD+
100R or higher *
R
TX/TD-
RX/RD+
R
100R or higher *
CTS/RD-
RG
11