User manual
 RS-232 Connections 
Manual Documentation Number: ESP901-902_4105m  Appendix A  71 
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 
A
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A
:
:
R
R
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S
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-
2
2
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Serial Server DB-9 Pin-outs in RS-232 Mode 
RS-232 
Signal Name 
DTE RS-232 DB-9M 
Pin 
Carrier Detect  In  DCD  1 
Receive Data  In  RXD  2 
Transmit Data  Out  TXD  3 
Data Terminal Ready  Out  DTR  4 
Signal Ground  ---  GND  5 
Data Set Ready  In  DSR  6 
Request To Send  Out  RTS  7 
Clear To Send  In  CTS  8 
Ring Indicator  In  RI  9 
Figure 60.  RS-232 Connections in a DB-9 Connector 
RS-232 Connections 
72  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 Straight-through Cable Connections 
In the RS-232 mode, the Serial Server’s ports are configured as DTEs 
like a computer. If the device connected to the 
Serial Server is 
configured as a DCE use a straight through cable wired as shown 
below: 
Figure 61.  Straight-through DB-9 to DB-9 RS-232 Serial Cable 
RS-232 Crossover (null modem) Cable Connections 
When connecting to a PC or another DTE device, use a crossover cable 
(also called a null modem cable). 
Figure 62. Crossover DB-9 to DB-9 RS-232 Serial Cable 
RS-232 Signal Names  DB-9 
Pin# 
Connections DB-9 
Pin# 
Signal
Carrier Detect  CD  1    1  CD 
Receive Data  RD  2    2  RD 
Transmit Data  TD  3    3  TD 
Data Terminal Ready  DTR  4    4  DTR 
Signal Ground/Common GND 5  5 GND 
Data Set Ready  DSR  6    6  DSR 
Request to Send  RTS  7    7  RTS 
Clear to Send  CTS  8    8  CTS 
Ring Indicator  RI  9    9  RI 
RS-232 Signal Names  DB-9 
Pin# 
Connections DB-9 
Pin# 
Signal 
Carrier Detect  CD  1    1  CD 
Receive Data  RD  2    2  RD 
Transmit Data  TD  3    3  TD 
Data Terminal Ready  DTR  4    4  DTR 
Signal Ground/Common  GND  5    5  GND 
Data Set Ready  DSR  6    6  DSR 
Request to Send  RTS  7    7  RTS 
Clear to Send  CTS  8    8  CTS 
Ring Indicator  RI  9    9  RI 










