Multitech MultiModem II BA-Series, User Manual

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MultiModemBA User Guide
8.3 Digital Loopback Test/V.54 Loop 2 (Local/Manual)
In this test, your modem must be On-Line with another modem that can respond to a request for
Digital Loopback, such as another MultiModem. The Digital Loopback Test is an on-line test that
loops data sent from one modem across the phone line to another modem, then back to the first
modem. See Figure 8-2.
There are two ways to put a modem into Digital Loopback mode.
1. Locally or Manually, described here in section 8.3.
2. Remotely or Automatically, see section 8.4.
Note: The Digital Loopback Tests can only be used with the modem in Normal mode (error
correction off).
UUUUU
UUUUU
Computer or Terminal Local MultiModem Remote MultiModem Computer or Terminal
Digital Analog Digital Analog
ATU3
Figure 8-2. Digital Loopback Test (local/manual)
In this test the local modem is placed in Digital Loopback mode. Data is entered and transmitted from
the remote modem (which is not in digital loopback mode), sent across the phone line to the local
modem and looped back to the remote modem.
The test procedure is as follows:
1. Go into Terminal mode. Type AT and hit ENTER; you should get an OK message.
2. Dial the remote modem by entering the Dial command and the phone number, to establish On-
line mode.
3. Type the Escape Sequence (+++AT<CR> or <BREAK>AT<CR>) which brings your modem into
Command mode, while still maintaining the pseudo On-line mode with the remote modem.
4. Type ATU3 from the local PC and hit ENTER. Once you receive an OK message from your
modem (if responses are enabled), the local modem is placed in Digital Loopback mode.
5. Data is typed from the remote keyboard. For this test, typing multiple upper case "U" characters
is a good way to send an alternating test pattern of ones and zeros. The data received by the
local modem will enter its analog receiver, be converted to digital data, be reconverted into
analog, and then looped through its transmitter back to the remote modem. Your modem passes
this test if the data entered from the remote keyboard is the same as the data received on the
remote monitor.
6. When testing is complete, you may end the test by typing an Escape Sequence (+++AT<CR> or
<BREAK>AT<CR>) to bring your modem into 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 AT0 and hit ENTER. If you wish to terminate the call, type ATH and hit
ENTER to hang up.