PORTABLE USB MODEM

B.2 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 modem’s receiver, converted into digital form, and then sent to your monitor for verification. No connection to the phone line is required.

AT&T1

CONNECT

UUUUUUUUU

UUU

Digital Analog

Computer or Terminal

Portable USB Modem

Local MultiModem

Figure B-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 displayed on your monitor. The TD and RD LEDs should flash when a character is entered.

5.To exit the test, type the escape sequence +++AT and press ENTER. This puts the modem in online command mode. Then type either AT&T or ATH to return to command mode.

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Black Box MD403A user manual Local Analog Loopback Test V.54 Loop, Figure B-1. Local analog loopback test

MD403A specifications

The Black Box MD403A is a powerful and versatile device widely recognized for its advanced technology and its ability to streamline data communication. Ideal for both personal and professional use, the MD403A is designed to cater to various environments, from small offices to larger enterprises.

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