Rs-422 mode, Rs-485h mode, Rs-485f mode – B&B Electronics ESR904 - Manual User Manual

Page 23: Rs-485 receiver biasing

Making the Hardware Connections

Manual Documentation Number: ESR90x-5012m

Chapter 2

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RS-422 Mode

the currently selected serial port is configured as an RS-422

interface supporting four RS-422 signal channels with full duplex operation
for

Receive

Transmit

RTS

(Request To Send) and

CTS

(Clear To Send).

The data lines are differential pairs (A & B) in which the B line is positive
relative to the A line in the idle (mark) state. Ground provides a common
mode reference. To use handshaking, Flow Control must be set to RTS/CTS
during configuration.

RS-485H Mode

the currently selected port is configured as a two-wire RS-

485 interface supporting DataB(+) and DataA(-) signal channels using half-
duplex operation. The data lines are differential with the Data B line positive
relative to Data A in the idle (mark) state. Ground provides a common mode
reference.

RS-485F Mode

the currently selected port is configured as a four-wire RS-

485 interface supporting transmit lines TXDB(+) and TXDA(-) and receive
lines RXDB(+) and RXDA(-) for full duplex operation. The lines are
differential with the B line positive relative to A in the idle (mark) state.
Ground provides a common mode reference.

RS-485 Receiver Biasing

can be implemented from the Serial Server if the

network does not supply it. Remove the four screws from the cover of the
Serial Server, slide the cover off and re-position the bias jumpers as indicated
in the diagrams and tables below. Note that ESR Serial Servers provide
separate jumpers for RS-485 half duplex and RS-422/485 full duplex
operation. Also, the ESR901 provides separate jumpers for the terminal block
and DB-9 connectors. Biasing jumpers are also provided for CTS inputs.