User's Manual

XT55/56 Hardware Interface Description
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XT55/56_hd_v02.06a Page 33 of 125 17.12.2004
3.3.1.3 Turn on the GSM part of XT55/56 using the GSM_POWER signal
As detailed in Chapter 3.5.4, the charging adapter can be connected regardless of the
module’s operating mode (except for Alarm mode).
If the charger is connected to the charger input of the external charging circuit and the
module’s GSM_POWER pin while XT55/56 is off, processor controlled fast charging starts
(see Chapter 3.5.3). The GSM part of XT55/56 enters a restricted mode, referred to as
Charge-only mode where only the charging algorithm will be launched.
During the Charge-only mode XT55/56 is neither logged on to the GSM network nor are the
serial interfaces fully accessible. To switch to normal operation and log on to the GSM
network, the GSM_IGT line needs to be activated.
3.3.1.4 Turn on the GSM part of XT55/56 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 the GSM part of the XT55/56 to wake up whilst the internal voltage regulators
are 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 part of XT55/56 was powered down by AT^SMSO. Once the alarm is timed out and
executed, XT55/56 enters the Alarm mode. This is indicated by an Unsolicited Result Code
(URC) which reads:
^SYSSTART ALARM MODE
Note that this URC is the only indication of the Alarm mode and will not appear when
autobauding was activated (due to the missing synchronization between DTE and DCE upon
start-up). Therefore, it is recommended to select a fixed baudrate before using the Alarm
mode. In Alarm mode only a limited number of AT commands is available. For further
instructions refer to the AT Command Set.
Table 5: AT commands available in Alarm mode
AT command Function
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 range, enable/disable URCs to report critical temperature
ranges
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.