Multitech MMH900 User Manual page 154

4. Type ATU2 and hit ENTER. The local modem responds to this
command by transmitting an unscrambled marking signal, which
causes the remote modem to place itself in Digital Loopback mode.
Then the local modem exits Command mode and enters pseudo On-
line mode.
5. Type 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. The data received by the remote modem will
enter its analog receiver, be converted to digital data, be reconverted
into analog, and then looped through its transmitter back to the local
modem. Your modem passes this test if the data entered from the
local keyboard is the same as the data received on your monitor.
Appendix I - Testing Your MMH 2834
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