Multitech MMH900, User Manual

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Appendix J - Internal MMH2834 Composite Link Modem Commands
J.1.7 RS232C Interface Control Commands
Data Terminal Data Terminal Ready (DTR) on pin 20 of the RS232C interface
Ready Control is required in order for the MMH2834 to operate. A high DTR
signal tells the modem that the device to which it is connected
&D is active, or "ready" to communicate through the modem.
DTR has some other MMH2834 functions. DTR can be used to
trigger a dialing sequence, called DTR Dialing. The condition of
DTR can also be used to cause the modem to reset to its default
parameters, just as if you had given the modem an ATZ
command. To do this, enter the command AT&D3 and hit
RETURN. The modem will now reset itself whenever DTR is
dropped from On to Off, and will also go on-hook (hang up) if it
is on-line.
Entering AT&D0 or AT&D causes the MMH2834 to ignore DTR.
Entering AT&D1 causes the modem to go on-hook (hang up)
with loss of DTR. The modem enters Command mode when
DTR goes high again. Auto-answer is disabled while DTR is low.
Entering AT&D2 causes the modem to go on hook with loss of
DTR. The modem enters command mode when DTR goes high
again.