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Hardware Description
3.4
TURNING THE UNIT ON/OFF
This section describes the methods available to turn the c18 unit on and off.
3.4.1
On/Off Circuitry
The unit does not power-up automatically by connecting the power. There are two ways to turn on the c18 unit:
• Using the AUDIO_OUT_ONOFF pin
• Using the Ignition pin
It is recommended to use the AUDIO_OUT_ONOFF line to power-on or power-off the c18.
The module should not be turned off by removing the supply voltage. If the c18 is powered off by disconnecting the
!
power to the unit, the c18 module does not shut down properly and does not complete the deregistration procedure
from the network.
Caution
3.4.2
Turning the Unit On/Off Using the AUDIO_OUT_ONOFF Pin
The c18 module can be turned on or off using the AUDIO_OUT_ONOFF line (pin #53 on the 70-pin connector, pin #14 on the
36-pin ZIF connector and pin #17 on the 28-pin DIN connector). The AUDIO_OUT_ONOFF line has dual functions, as follows:
• It serves as an audio output.
• It serves as an on/off signal.
It is internally pulled high, to approximately VCC -0.6V.
To turn the modem on, the AUDIO_OUT_ONOFF signal should be pulled to GND through a 4.7K resistor for a minimum of
two seconds. The signal should then be released, and the module will begin the power-up sequence. During the next six to seven
seconds, the module does not communicate (for example, it does not respond to AT commands if configured for RS232
communication). For a detailed description of UART signals at power-up, see "UART1" on page 24.
When using this signal as audio output, make sure to decouple the load with a capacitor. Connecting a load directly
without the capacitor alters proper module functionality. For more details concerning the audio interface, see
"Hands-free Audio (Auxiliary Audio) Interface" on page 30.
Note
To turn the module off, the AUDIO_OUT_ONOFF signal should be pulled to GND through a 4.7K resistor for a minimum of
two seconds. The signal should then be released. This initiates the power-down sequence, which includes deregistration from
the network. The process takes approximately three to eight seconds (typically five seconds). After the module has powered
down, the voltage supply can be disconnected from the module.
The module should not be turned off by removing the supply voltage. If the c18 is powered off by disconnecting the
!
power to the unit, the c18 module does not shut down properly and does not complete the deregistration procedure
from the network.
Caution
18
98-08901C63-A
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