Connecting Serial Devices
DeviceMaster UP User Guide
: 2000451 Rev. C
- 27
DB9 Serial Cables and Loopback Plugs
DB9 Serial Cables and Loopback Plugs
You can build your own null-modem or straight-through DB9 serial cables using
the following subsections.
This illustrates the DB9 connector signals.
Note:
If you are using a DB9 to RJ45 adapter, see
DB9 Loopback Plugs
Loopback connectors
are DB9 female serial port plugs, with pins wired together as
shown, that are used in conjunction with application software (Test Terminal or
Minicom) to test serial ports. The DeviceMaster UP is shipped with a a single
loopback plug (RS-232/422).
Wire the following pins together to build additional plugs or replace a missing RS-
232 loopback plug:
•
Pins 1 to 4 to 6
•
Pins 2 to 3
•
Pins 7 to 8 to 9
Wire the following pins together for an RS-422 loopback plug:
•
Pins 2 to 3
•
Pins 7 to 8
DB9 Connector Pinouts
Pin
RS-232
RS-422
RS-485
1
DCD
Not used
Not used
2
RxD
RxD-
Not used
3
TxD
TxD-
TxD/RxD-
4
DTR
Not used
Not used
5
GND
Not used†
Not used†
6
DSR
Not used
Not used
7
RTS
TxD+
TxD/RxD+
8
CTS
RxD+
Not used
9
RI
Not used
Not Used
†
Pin 5 is tied to ground on the board, but is
not used in the cable.
Pin 1
Pin 6
DB9 Male
RS-232
RI
CTS
RTS
DSR
GND
DTR
TxD
RxD
CD
Pin 1
Pin 6
DB9 Male
RS-422
Not used
RxD+
TxD+
Not used
Not used*
Not used
TxD-
RxD-
Not used
Pin 1
Pin 6
DB9 Male
RS-485
Not used
Not used
TxD/RxD+
Not used
Not used*
Not used
TxD/RxD-
Not used
Not used
*
Pin 5 is tied to ground on the board,
but is not used in the cable.
Pin 1
Pin 5
Pin 6
Pin 9
RS-232 Only
(Back View)
The RS-232 loopback plug
also works for RS-422.
Pin 1
Pin 5
Pin 6
Pin 9
RS-422 Only
(Back View)
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