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Operation
3.1 Switch ON the modem
There are two ways to switch on the modem, once power is applied:
assert TO_IN to high level for > 1s
activate the RS232 control line DTR
The modem is fully operational after 4 seconds. Logging onto a network may take longer than this and
is outside the control of the modem. The modem can be configured to start up at the time power is
applied by permanently tying power connector signals TO_IN (pin 4) and VCC (pin 1) together. In this
case DTR must be used to switch the modem on again after it has been switched off or reset, while
power is still applied.
DTR must be cycled from low to high.
The TO_IN signal requires a positive "edge" (a sharp" signal transition from low to high)
to turn the modem on. This transition should be a rising signal from 0V (GND) to VCC, or
at least a large fraction of that voltage range, and must be applied at the same time as
VCC or after it. Very slow transitions (significantly slower than many milliseconds) or
very small transitions (e.g. only few volts instead of 0V to VCC) will not turn on the
module (since they are not considered to be a "positive edge").
Although this will not be an issue in almost all typical applications of the modem, please consider
following points:
Large capacitors in your power supply which will lead to slow leading and falling edges (issue does not
apply with modern stabilized switching regulator power-adaptors) AND TO_IN tied in parallel to VCC
(instead of separate dedicated digital signal)
Slow analogue signals used to assert TO_IN
TO_IN signal not before VCC
All 3 cases above might prevent the modem from recognizing the power-up signal this is no failure of
the modem itself, the same would apply to almost any electronic device that provides a separate
"power-on" or "reset" signal.
If you are in doubt, please
Use the mains power adapter that is provided by your distributor and is know to work properly with your
modem
Make sure that your signal and system design is according to the above
Consult our support team that will be more than happy to assist you.
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