B&B Electronics ESR902 User Manual

Manual Documentation Number: ESR90x-0508m 

Chapter 2 

13 

B&B Electronics Mfg Co Inc – 707 Dayton Rd - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com 

B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com 

In 

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

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

, 

, 

(Request To Send) and 

 (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.  

In 

 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.  

In 

 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. 

 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.