I/O and Cabling Considerations
3.3.12 Device Wiring Considerations (Telco)
Consideration must be given to the wiring scheme when a device such as a terminal or serial
printer is to be connected to a serial port. The serial ports are considered DTE devices. To
connect the port to another DTE device (such as a VT200 terminal), you will need a crossover
wiring scheme somewhere in the cabling. (Communication between DTE-to-DTE devices
requires a crossover.) To connect the port to a DCE device (such as a modem), straight-through
wiring is required. In the standard Xyplex-supplied modular cabling options, listed in section
3.3.8, signals are directed to the correct pins in the adaptor (for example, the crossover is made
in the DROP adaptor, so that only one type of six-wire cable needs to be used) If you wish to
make your own cables, you must construct the cable with the appropriate wiring scheme.
Figure 3-18 illustrates a simple version of both crossover and straight-through wiring schemes
(this wiring diagram represents the minimum needed to connect a simple terminal).
Male Pinouts
Female Pinouts
Straight Through Cable
Cross Over Cable
Female Pinouts
Female Pinouts
XMT 2
RCV 3
GND 7
XMT 2
RCV 3
GND 7
XMT 2
RCV 3
GND 7
XMT 2
RCV 3
GND 7
Figure 3-18. Crossover and Straight-Through Wiring Schemes.
The crossover cable connects the serial port transmit data (XMT) line to the receive data (RCV)
line of the DTE device. Similarly, the RCV line crosses over to the XMT line of the DTE device.
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