MDR24X User’s Manual
10/26/2006
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
2
TxD
3
RxD
4
DSR
5
GND
6
DTR
7
CTS
8
RTS
NC
RI
CTS
DTE
DCE
Straight Through Cable
CTS
RTS
RTS
RXD
TXD
TXD
RXD
GND
GND
DCD
DCD
DSR
DSR
DTR
DTR
OEM Host/PC
MDR24X Modem
