User's Manual

Table Of Contents

MC55/56 Hardware Interface Description

Confidential / Preliminary

MC55/56_hd_v03.00 Page 30 of 104 16.08.2005

Figure 5: Timing of power-on process if VDDLP is fed from external source

3.3.1.3 Turn on MC55/56 using the POWER signal

As detailed in Chapter 3.5.3, the charging adapter can be connected regardless of the

module’s operating mode.

If the charger is connected to the charger input of the external charging circuit and the

module’s POWER pin while MC55/56 is off, processor controlled fast charging starts (see

Chapter 3.5.2). MC55/56 enters a restricted mode, referred to as Charge-only mode where

only the charging algorithm will be launched.

During the Charge-only mode MC55/56 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 /IGT line needs to be activated.

3.3.1.4 Turn on MC55/56 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 MC55/56 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

MC55/56 was powered down by AT^SMSO. Once the alarm is timed out and executed,

MC55/56 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.

3.0V

min. 100ms

max. 1ms

10ms

HiZ

BATT+

/IGT