Ot-systems FTD110DB-XXR3 Manual do Utilizador descarregar pdf (Página 12)

FTD110DB-XXR3 Series Installation & Operation Manual

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Dip switch settings for various types of data transmissions

Function / Switch No.

Sw. 3

Sw. 4

RS485 (2-Wire)

OFF

RS422/485 (4-Wire)*

OFF

RS232

OFF

* Factory setting [RS422/485 (4-Wire)]

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. 4.5 Termination of different Bus structures

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Ot-systems FTD110DB-XXR3 Manual do Utilizador Página 12