USB232U/485Ui
Page 20
4.3.2
The Loop Back Connections
The USB232U/485Ui can be separated from external serial interface influences such as the
signal cables, other devices and the applications program by performing a loop-back test. For
both RS232 and RS422/485 tests, it is necessary to make up a wrap connector using a 9-way
D-type free socket that mates with the port under test. Then run a terminal emulator such as
Hyper-Terminal.
Figure 4.4 shows the 9-way D-type connector wired for RS232 loop back testing. No
connections need to be made to the ground pin.
Signal Function
9-way
From
To
Pin
Pin
TxD
RxD
3
2
RTS
CTS
7
8
DTR
DSR and DCD
4
6 and 1
Figure 4.4 RS232 Loop-Back Test Connections
Figure 4.5 shows the 9-way D-type connectors wired for RS422/485 loop back testing. The
connections to be made are summarised in the following table. No connection needs to be
made to the ground pin.
Signal Function
9-way Amplicon
From
To
Pin
Pin
Tx-A
Rx-A'
4
8
Tx-B
Rx-B'
5
9
Figure 4.5 RS422/485 Loop-Back Test Connections
Loop-back testing is only appropriate to full duplex operation of the RS422/485 ports. See
Figure 2.1 for jumper settings.
4.3.3
Loop-back Testing Using A Terminal Emulator
Windows 98, 2000 and XP come supplied as standard with a Terminal Emulation package
called Hyper Terminal. This can be used for simple loop-back testing and is found in the
Accessories section from the START button.
Start Hyper-terminal and when prompted, enter a meaningful name such as Port 2 for COM2 or
Port 4 for COM4 etc. The software will not let you use COM2 etc, as these are reserved words.
9
8
GND
RI
DTR
CTS
TxD
RTS
RxD
DSR
DCD
7
6
5
4
3
2
1
9
8
Tx-B
Rx-B'
Tx-A
Rx-A'
RTS-A
CTS-B'
RTS-B
CTS-A'
GND
7
6
5
4
3
2
1
Summary of Contents for USB232U
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Page 11: ...USB232U 485Ui Page 5 Brighton East Sussex BN2 4AW England ...
