Ot-systems FTD110DBMicro Manuel d'utilisateur télécharger pdf (Page 11)

FT110DBMicro Series Installation & Operation Manual

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Dip switch settings for line terminations

Line Output Termination Line Input Termination

Function / Switch No.

Sw. 1

Line Output Terminated

Line Output Unterminated*

OFF

Function / Switch No.

Sw. 2

Line Input Terminated

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

1 2 ... 6 7 8 9 10 11 12 13 14 15

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Ot-systems FTD110DBMicro Manuel d'utilisateur Page 11