User manual
  Making Hardware Connections 
Manual Documentation Number: ESP901-902_4105m  Chapter 2  13 
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com 
B&B Electronics Ltd – Westlink Commercial Pk – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com 
Default Mode 
When 
Default Mode is selected and the server properties are Updated 
(
Saved) all the configuration settings return to their default values. 
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Refer to Chapter 5 for details on Serial Server Configuration settings. 
See Chapter 12 for Serial Server default parameters. 
Console Mode 
In Console Mode the Configuration Menu can be accessed from a PC 
by connecting its RS-232 serial port to the ESP901 serial port or 
ESP902 Serial Port 1. Since the computer is a DTE device, and the 
serial ports are configured as DTEs (with DB-9M connectors), a null 
modem crossover cable must be used. 
In 
Console Mode the default serial port settings are: 9600 baud, 8 data 
bits, No parity, and 1 stop bit. From Windows, HyperTerminal with 
VT100 terminal emulation can be used for Console Mode 
configuration. 
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Refer to Chapter 9 for details on Console Mode 
Upgrade Mode 
In Upgrade Mode firmware can be uploaded from a PC via its serial 
port to the ESP901 serial port or ESP902 Serial Port 1. Upgrading also 
can be accomplished via the network connection, using the ESP 
Manager software and a virtual COM port.  
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Refer to Chapter 8 for details on Upgrade Mode 
RS-232 Mode 
In RS-232 Mode the currently selected serial port is configured as an 
RS-232 interface supporting eight RS-232 signal lines plus Signal 
Ground and is configured as a DTE, like a computer. Signals are single 
ended and referenced to Ground. To use handshaking, Flow Control 
must be set to RTS/CTS during Configuration. 
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Refer to Appendix A for RS-232 connection pin-outs. 
Making Hardware Connections 
14   Chapter 2  Manual Documentation Number: ESP901-902_4105m 
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com 
B&B Electronics Ltd – Westlink Commercial Pk – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com 
RS-422 Mode 
In 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. 
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Refer to Appendix B RS-422 connection pin-outs. 
RS-485 Mode 
In RS-485 Mode the currently selected port is configured as an RS-485 
interface supporting transmit (TX) and receive (RX) signal channels 
using 2-wire, 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. 
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Refer to Appendix C for RS-485 connection pin-outs. 
RS-485 Receiver Biasing 
RS-485 Receiver Biasing
 can be implemented from the Serial Server 
if the network does not supply it. Remove the two side-cover screws of 
the 
Serial Server, slide the cover off and re-position the bias jumpers 
(shown open in the figure below) to enable biasing (shorting). 
Figure 10.  Internal Setting to Select RS-485 Bias 
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(For more information on RS-485 Receiver Biasing, see B&B 
Electronics RS-422/485 Application Note available at www.bb-
elec.com) 










