External Connections - Quatech Asynchronous Communications Adapter for PCI bus DSCLP/SSCLP-100 User Manual

7 External Connections

RS-232-C devices are classified by their function as either Data Terminal
Equipment (DTE) or Data Communication Equipment (DCE). Generally, data
terminal equipment is defined as the communication source and data
communication equipment is defined as the device that provides a communication
channel between two DTE-type devices.
Terminal
DTE
Terminal
DTE
Figure 16 --- Use of DTEs and DCEs in a communications link
DTE- and DCE-type devices have complementary pinouts to allow
terminals and modems to be connected directly using a one-to-one cable as shown
in Figure 16. In many applications, DCEs are unnecessary, and in these cases a
cable called a "null modem cable" or "modem eliminator cable" is used to directly
connect two DTE-type devices. A typical null modem cable is also shown in
Figure 17.
(3) (3)
RxD RxD
(2) (2)
TxD TxD
(4) (4)
RTS RTS
(5) (5)
CTS CTS
(20) (20)
DTR DTR
(6) (6)
DSR DSR
(8) (8)
DCD DCD
(22) (22) RI
(7) (7)
GND GND
Typical DTE-to-DCE cable
Figure 17 --- Cabling requirements for RS-232-C devices
32
RS-232-C
RS-232-C
(3)
TxD
RxD (2)
CTS (4)
(5)
RTS
(20)
DSR
DTR (6)
(8) (8)
DCD DCD
RI RI (22) (22)
(7) (7)
GND GND
(cables using 25-pin connectors shown)
Modem
DCE
Telephone
line
Modem
DCE
(3)
RxD
(2)
TxD
(4)
RTS
(5)
CTS
(20) DTR
(6)
DSR
(8)
DCD
(22) RI
(7)
GND
Typical DTE-to-DTE null modem cable
DSCLP/SSCLP-100 User's Manual
(3)
RxD
(2)
TxD
(4)
RTS
(5)
CTS
DTR (20)
(6)
DSR
DCD (8)
RI (22)
(7)
GND