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MT5634ZBA-USB User Guide
Local Digital Loopback Test (V.54 Loop 2)
The local digital loopback test is identical to the remote digital loopback test with one
exception. Instead of using your modem to signal a remote modem to place itself in
digital loopback mode, your modem is placed in digital loopback mode while the remote
modem is not. Data is entered and transmitted from the remote modem, sent across the
phone line to your modem, and looped back to the remote modem.
UUUUUUUUU
UUUUU
Computer or Terminal Local MultiModem Remote MultiModem Computer or Terminal
Digital Analog DigitalAnalog
AT&T3
OK
Figure C-3. Local digital loopback test
Test Procedure
1. Open your communications software and go into terminal mode. Type AT and press
ENTER; you should get an
OK
message. Type AT\N and press ENTER to disable
error correction.
2. Dial the remote modem and establish your online connection.
3. Type the escape sequence +++AT and press ENTER to bring your modem into
online command mode.
4. Type AT&T3 and press ENTER. Once you receive an
OK
message from your
modem (if responses are enabled), your modem is placed in digital loopback mode.
5. Have someone enter data from the remote keyboard. For this test, typing multiple
uppercase
U
characters is a good way to send an alternating test pattern of binary
ones and zeros. The data received by your modem enters its analog receiver, is
converted to digital data, is reconverted into analog, and then is transmitted back to
the remote modem. Your modem passes this test if the data received on the remote
monitor is the same as the data entered from the remote keyboard.
6. To exit the test, type the escape sequence +++AT and press ENTER. This puts the
modem in online command mode. The modem should respond with an
OK
message.
If you wish to stay on line with the remote modem for normal data transmission, type
AT&T and press ENTER to exit the test, then type ATO and press ENTER to return
on line. If you wish to terminate the call, type ATH and press ENTER to hang up.