User manual
 RS-232 Connections 
Manual Documentation Number: ESP904-0504  Appendix  57 
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 Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
A
A
P
P
P
P
E
E
N
N
D
D
I
I
X
X
A
A
:
:
R
R
S
S
-
-
2
2
3
3
2
2
C
C
O
O
N
N
N
N
E
E
C
C
T
T
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O
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N
N
S
S
ESP904 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 41. RS-232 Connections in a DB-9 Connector 
 RS-232 Connections 
58  Appendix A  Manual Documentation Number: ESP904-0504 
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 Park – 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 ESP904’s ports are configured as DTEs like a 
computer. If the device connected to the ESP904 is configured as a DCE use 
a straight through cable wired as shown below: 
Figure 42. Straight-through (DTE to DCE) DB-9 to DB-9 Serial Cable 
with RS-232 Signal Designations 
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 43. Crossover (DTE to DTE) DB-9 to DB-9 Serial Cable with 
RS-232 Signal Designations 
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 










