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Local Analog Loopback Test (V.54 Loop 3)
In this test, data from your computer or terminal is sent to your mo-
dem’s transmitter, converted into analog form, looped back to the mo-
dem’s receiver, converted into digital form, and then sent to your
monitor for verification. No connection to the phone line is required.
Computer or Terminal Local MultiModem
Digital Analog
AT&T1
CONNECT
UUUUUUUUU
UUU
Figure C-1. Local analog loopback test.
Test procedure
1. Connect the modem to your computer. Using your communication
program, set the desired baud rate and go into terminal mode.
2. Type AT&T1 and press ENTER. This places your modem in analog
loopback mode in the originate mode. A
CONNECT
message should
appear on your display. The modem is now out of command mode
and in a pseudo-online mode.
3. Note that the CD LED is on. If you are set for 14,400 bps or higher,
a speed LED should be on. If the CD LED is not on, there is a defect
in your modem.
4. Enter characters from your 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 characters entered should be