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Local Optical Loopback Test
To perform this local optical test, all the front panel SW2 dip switches should be to the up "Off" position.
1. Set up the bench test as illustrated in Figure 7 below. Make sure to use the correct type of fiber optical
jumper cables (either Single Mode or Multimode according to the specifications of the TC1720s).
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 tester should indicate a Synchronous signal being received indicating that the RS-422/
449 electrical signal is transmitted and received okay.
7. Verify that the "TxD," "RxD," "TxClk," "RxClk," "RxA," "PWRA or PWRB," and "Vcc" LEDs are solidly
lit on the TC1720. Note, the "ALARM" LED will be "Off" since there is optical fiber cable(s) 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.
BERT Test Set
with RS-422/449
Figure 7. Local Optical Loopback Test Connection Diagram
DB37 Female
Cable
ALARM
(Optional)
OPTIC
TxB
(Optical redundant
models only)
-14-
TC1720
(Optional Dual Optics)
User's Manual
Rev. 1.4
DC Power Supply
12VDC@ 500mA
Male DB37
PWR
PWR
RS-422/449
B
ASYNC/SYNC
FIBER OPTIC MODEM
OPTIC
RxB
TxA
RxA
A
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