TC1720
(Optional Dual Optics)
User's Manual
Rev. 1.4
-13-
Local Electrical Loopback Test
1.
Set up the bench test as illustrated in Figure 6 below.
2.
Make sure your BERT tester is turned on and configured as an RS-422/499 DTE device if the unit is
DCE.
3.
Connect the DB37 female adapter (check pin assignments on page 3) from the BERT tester to the
TC1720’s DB37 male connector (on the rear panel).
4.
Set the BERT test set to the same (or as close to the same) data rate as the application you plan to connect
to (typically 19.2Kbps through 128Kbps Synchronous).
5.
The data bits should be selected as ‘8 bits’ and the data pattern should be set to ‘2047’ on the BERT
tester.
6.
At this point, the following LEDs should be observed on the TC1720 unit: The "TxD," "TxClk," "PWRA
or PWRB," "Vcc," and "ALARM" should be solidly lit. Note, the "ALM" LED will be solidly lit and the
"RxA" LED will be flashing since there is no optical fiber cables connected. All other LEDs should be
off.
7.
Now, turn the front panel SW2-2 (LOCLB) dip switch to the down "On" position to enable the Local
Loopback test function.
8.
At this point, the tester should indicate a Synchronous signal being received indicating that the RS-422/
449 electrical signal is transmitted and received okay.
9.
Verify that the "TxD," "RxD," "TxClk," "RxClk," "ALARM," "PWRA or PWRB," and "Vcc" LEDs are
solidly lit. Note, the "ALM" LED will be solidly lit and the "RxA" LED will be flashing since there is no
optical fiber cables connected. All other LEDs should be off.
You should not see any bit errors. To verify this, inject an error using the BERT tester to see if it will
be recorded by the tester, then verify that no additional errors appear after the user injected error.
10.
When done with this test, make sure to return the front panel SW2-2 (LOCLB) dip switch to the up "Off"
position to disable the Local Loopback test function and proceed with other tests.
Figure 6. Local Electrical Loopback Test Connection Diagram
ALARM
DB37 Female
Cable
BERT Test Set
with RS-422/449
RS-422/449
ASYNC/SYNC
FIBER OPTIC MODEM
TxB
TxA
RxB
OPTIC
OPTIC
(Optional)
RxA
PWR
A
PWR
B
DC Power Supply
12VDC@ 500mA
Male DB37
