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CL4424 User’s Manual
6/21/2005 11
2.1 RS-232
RS-232 is a single ended data transmission protocol. The RS-232 signals are represented by
voltage levels with respect to a system common (power / logic ground). The "idle" state (MARK)
has the signal level negative with respect to common, and the "active" state (SPACE) has the
signal level positive with respect to common. RS-232 has numerous handshaking lines (primarily
used with modems), and also specifies a communications protocol.
Figure 5- RS-232 Male/Female Connector Pin out
RS-232 DB9 Female
Connector RS-232 DB9 Male Connector
Figure 6- DCE to DTE Interface
Pin Description
1
DCD
2 RxD
3 TxD
4 DTR
5 GND
6 DSR
7 RTS
8 CTS
9 RI
Pin Description
NC
DCD
2TxD
3RxD
4DSR
5GND
6DTR
7CTS
8RTS
NC RI
C
T
S
DTE
DCE
Straight Through Cable
CTS
RT
S
RT
S
RXD
TXD
TXD
RXD
GND
G
ND
D
C
D
D
C
D
D
SR
D
SR
DT
R
DT
R
OEM Host/PC
CL4424 Modem