User manual
 RS-232 Connections 
Manual Documentation Number: ESP901-902_4105m  Appendix A  73 
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-232 Straight-through DB-9 to DB-25 Conversion 
Connections 
Figure 63.  DB-9 to DB-25 Straight-through Cable Connections 
RS-232 Crossover DB-9 to DB-25 Conversion Connections 
Figure 64.  DB-9 to DB-25 Crossover (null modem) Cable Connections 
RS-232 Connections 
74  Appendix A  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-232 DTE Loopback Connections 
Figure 65.  Loopback Connections for RS-232 
For Transmit and Receive loopback, connect only those lines. 
When Flow Control setting on the 
Serial Server is set for RTS/CTS, 
those lines must be looped. Usually DTR and DSR must also be 
looped. The Flow Control setting for the program must match the 
Server settings. The CD connection is needed by some terminal 
programs to simulate Carrier. 










