OT Systems FTD110DBMicro User Manual
Page 11
FT110DBMicro Series Installation & Operation Manual
11
Dip switch settings for line terminations
Line Output Termination
Line Input Termination
Function / Switch No.
Sw. 1
Line Output Terminated
ON
Line Output Unterminated*
OFF
Function / Switch No.
Sw. 2
Line Input Terminated
ON
Line Input Unterminated*
OFF
* Factory setting (Line Output and
Line Input “Unterminated”)
Industrial practice for line terminations
For RS422 4-wire communication, it is suggested to keep the input and output lines
terminated in the ONE Tx to ONE Rx configuration.
For RS485 2/4-wire communication, the RS485 device can be disabled to stay in a Hi-Z
state. It is very important that the data lines have to be terminated with a resistor being connected
across the pair wires so as to eliminate the residual standing signal waves on the lines in the Hi-Z
line condition. So, it is recommended that the lines should be terminated with the appropriate
resistance. When more than one RS485 device are connected in a daisy-chain configuration,
only the farthest device on the loop, i.e. the device located at the end of the line, should be
terminated; whereas the middles ones are set to “Unterminated” status. See the figure 4.6 below
for reference.
(a) RS485/422 4-wires Bus structure
(b) RS485 2-wire Bus structure
Fig. 4.6 Termination of different Bus structures