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Local Electrical Loopback Bench Test
Purpose:
This test loops the incoming RS-232, RS-422 or RS-485 electrical signal back to the
output terminal blocks in order to verify the cable connections, the electrical interface
driver, signal polarity (for RS-422/RS-485) and the receiver's Integrated Circuitry.
Equipment
Requirements:
One (1) Bit Error Rate Test (BERT) Set with appropriate interface module.
Procedure:
Set up the bench test as shown in Figure 15. Set SW1 (LOCLB) to the Right position.
Connect a BERT tester to the IN(-) and IN(+) terminal blocks. Set the tester up as a
DTE device if RS-530 or RS-449 interface is used. "TD" and "RD" LEDs should light
on the TC1540, indicating the status of the looped signal. The BERT tester should
indicate a "SYNC" signal. This test should be performed on each individual unit in the
application.
Connect TC1540 to RS-530 DTE device
RS-530
DTE DEVICE
(DB25)
2
Tx-
Tx+ 14
3
Rx-
Rx+ 16
7
SIG
GND
Connect TC1540 to RS-449 DTE device
RS-449
DTE DEVICE
(DB37)
4
Tx-
Tx+ 22
6
Rx-
Rx+ 24
19
SIG
GND
Figure 17.
TC1540
IN-
IN+
OUT-
OUT+
SIG
GND
TC1540
IN-
IN+
OUT-
OUT+
SIG
GND
Local Loopback Bench Test Connection Diagram
- 18 -
Connect TC1540 to RS-232 DTE device
RS-232
DTE DEVICE
(DB25)
2
Tx-
3
Rx-
7
SIG
GND
RS-232,RS-422,RS-485
To BERT tester
to/from TTL conversion
TC1540D User's Manual
Rev. 1.2
TC1540
IN-
OUT-
SIG
GND
TC1540
Local loopback
SW1 to right
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