User manual

CEP AG Revision 0.9

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Page 11 of 26

2.8 Mini USB audio interface:

Signal

MIC -

EAR -

MIC +

EAR +

not connected

3 Operation

3.1 Switching 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.

Note: DTR must be cycled from low to high.

Note: 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”).