Specifications

TC35 / TC37 Hardware Interface Description
TC35_37_HD_02_V03.10 - Released Page 32 of 92 21.12.2001
3.3.1.3 Turn on GSM engine using the POWER lines
As detailed in Chapter 3.2.2.3, the charging adapter can be connected regardless of the
GSM engine's operating mode (except for Alarm mode).
If the charger is connected to the POWER lines while the GSM engine is off, only the
charging algorithm will be launched. The GSM engine runs in a restricted mode, referred to
as Charge-only mode.
During the Charge-only mode the GSM engine is neither logged on to the GSM network nor
is the RS-232 interface fully accessible. When the minimum voltage of 3.2V is achieved
within 60 minutes the charging process proceeds to software controlled charging. To switch
to normal operation and log on to the GSM network, the IGT line needs to be activated.
3.3.1.4 Turn on GSM engine using the RTC (Alarm mode)
Another power-on approach is to use the RTC, which is constantly supplied with power from
a separate voltage regulator in the power supply ASIC. The RTC provides an alert function
which allows to wake up the GSM engine while power is off. To prevent the engine from
unintentionally logging into the GSM network, this procedure only enables restricted
operation, referred to as Alarm mode. It must not be confused with a wake-up or alarm call
that can be activated by using the same AT command, but without switching off power.
Use the AT+CALA command to set the alarm time. The RTC retains the alarm time if the
GSM engine was powered down by AT^SMSO. Once the alarm is timed out and executed,
the GSM engine enters into the Alarm mode. This is indicated by an Unsolicited Result Code
which reads:
^SYSSTART ALARM MODE
In Alarm mode only a limited number of AT commands is available. For further instructions
refer to the AT Command Set.
Table 6: AT commands available in Alarm mode
AT command Use
AT+CALA Set alarm time
AT+CCLK Set date and time of RTC
AT^SBC In Alarm mode, you can only query the present current consumption and
check whether or not a charger is connected. The battery capacity is
returned as 0, regardless of the actual voltage (since the values measured
directly on the cell are not delivered to the module).
AT^SCTM Query temperature of GSM engine
AT^SMSO Power down GSM engine
For the GSM engine to change from the Alarm mode to full operation (normal operating
mode) it is necessary to drive the ignition line to ground. This must be implemented in your
host application as described in Chapter 3.3.1.1. If your application is battery powered note
that charging cannot be started while the engine is in Alarm mode, i.e. charging will not
begin even though the charger connects to the POWER lines. See also Chapter 3.3.5 which
summarizes the various options of changing the mode of operation.
If your host application uses the SYNC pin to control a status LED as described in Chapter
3.8.2.2, please note that the LED is off while the GSM engine is in Alarm mode.