Specifications

MULTI-FUNCTION LINE DRIVER

5.3.1 L

OCAL

NALOG

OOPBACK

(LAL)

The Local Analog Loopback (LAL) test checks the operation of the local

Multi-Function Line Driver, and is performed separately on each unit. Any

data sent to the local Multi-Function Line Driver in this test mode will be

echoed back (returned) to the user device. For example, characters typed on

the keyboard of a terminal will appear on the terminal’s screen. To perform

an LAL test, follow these steps:

1. Activate LAL. You can do this in either of two ways. One is to move the

right-hand top-panel slide switch labeled “LOOP” to the “LAL” (down)

position. The other is to raise the signal on Pin 18 of the RS-232

interface (switch SW2 position 8 must be “Off”—see Section 3.3). Once

LAL is activated, the MFLD’s transmit output is connected to its own

receiver. The Test LED should light.

2. Verify that the attached DTE is operating properly and can be used for

a test.

3. Move the left-hand top-panel slide switch labeled “BERT” to the “511”

(down) position. This will activate the V.52 BERT test mode and inject a

511 test pattern into the local loop. If any errors are present in the loop,

the Error LED will blink sporadically.

4. If the BERT test indicates no errors are present, move the “BERT” switch

to the

“up”

position to activate the “511/E” test with periodic errors. If

this test is working properly, the Error LED will blink regularly. A

successful 511/E test will confirm that the loop is in place, and that the

Multi-Function Line Driver’s built-in 511 generator and detector are

working properly.

5. If the BERT test indicates that errors are present, make sure that the

Multi-Function Line Driver is plugged into the DTE properly. (If the

MFLD is connected to a DTE across RS-232 cable, make sure the cable is

pinned straight through, is properly plugged in on both ends, and is not

longer than 6 ft. [1.8 m]. If the MFLD is connected to a DCE, make sure

that the connecting cable is properly cross-pinned according to Table 4-3

on page 19, is properly plugged in on both ends, and is not longer than

6 ft. [1.8 m].) Also, make sure that the MFLD is configured properly.

Then recheck your DTE equipment. If you still get errors and can’t find

the cause, call Black Box for technical support (see Section 6.1).