Appendix B Serial Port Information
©
National Instruments Corporation
B-7
Serial for Windows NT
Figure B-5 shows straight-through cabling in a DTE-to-DCE interface.
Pin 2
Rx D
Tx D
Rx D
Tx D
Pin 2
Pin 2
Pin 3
Pin 3
Pin 3
Pin 3
Pin 2
DTE
DCE
DCE
DTE
Figure B-5.
Straight-Through Cabling in a DTE-to-DCE Interface
Straight-through cabling is still the standard method to connect a modem
to your PC. However, because many applications use serial
communication to connect two or more DTEs without modems, the
cabling becomes more complicated. If two DTEs are wired together using
a straight-through cable, one transmitter is connected to the other
transmitter, and one receiver is connected to the other receiver. In this
setup, no transmissions can occur. Thus, these applications must use a
cabling scheme that connects the transmitter on one device to the receiver
on the other device and vice versa. This method is known as null-modem
cabling, because it replaces the two modems that traditional RS-232
applications would require between the two DTEs. You should use a
null-modem cable to communicate from one serial port to another.
Figure B-6 shows null-modem cabling in a DTE-to-DCE interface.
Rx D
Tx D
Rx D
Tx D
Pin 2
Pin 3
Pin 3
Pin 2
DTE
DTE
Figure B-6.
Null-Modem Cabling in a DTE-to-DCE Interface
