- 18 -
TC1540D User's Manual
Rev. 1.2
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.
Figure 17. Local Loopback Bench Test Connection Diagram
TC1540
SW1 to right
Local loopback
RS-232,RS-422,RS-485
to/from TTL conversion
To BERT tester
Connect TC1540 to RS-530 DTE device
RS-530
DTE DEVICE
(DB25)
TC1540
Tx-
2
Rx-
3
Tx+ 14
Rx+ 16
IN-
OUT-
IN+
OUT+
SIG
GND
SIG
GND
7
Connect TC1540 to RS-232 DTE device
RS-232
DTE DEVICE
(DB25)
TC1540
Tx-
2
Rx-
3
IN-
OUT-
SIG
GND
SIG
GND
7
Connect TC1540 to RS-449 DTE device
RS-449
DTE DEVICE
(DB37)
TC1540
Tx-
4
Rx-
6
Tx+ 22
Rx+ 24
IN-
OUT-
IN+
OUT+
SIG
GND
SIG
GND
19
