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5.1
Local Analog Loopback Test/V.54 Loop 3
In this test, data from your computer or terminal is sent to your modem's
transmitter, converted into analog form, looped back to the receiver,
converted into digital form and then received back at your monitor for
verification. No connection to the phone line is required. See Figure 5-1.
Computer or Terminal
UUUU
Type ATU0 or ATU1,
then ENTER
Figure 5-1. Local Analog Loopback Test
The test procedure is as follows:
1. Connect the modem to your computer. With your communication
software, set the desired baud rate.
2. Type ATU0 (or ATU) and hit ENTER. This places your modem in
Analog Loopback mode, in the Originate mode. The modem is now out
of the Command mode and in a pseudo On-Line mode.
3. Once you receive a connect message (if responses are enabled), enter
data from your keyboard. For this test, typing multiple upper case "U"
characters is a good way to send an alternating test pattern of ones and
zeros.
4. For a more complete test, you should also test the modem in Answer
mode. To do this, you must "escape" from Originate mode by entering
an Escape Sequence (+++AT<CR> or <BREAK>AT<CR>) . Then type
Chapter 5 - Testing the Modem
Local MultiModem
Digital
Analog
57
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