Nokia 2608 Service Manual page 91

RM-376
System Module and User Interface
Power Key
When the power key is pressed, the PM enters the power-up sequence. Pressing the power key causes the
KPD_PWR_N (KPD_PWR_N pin in 2608 schematic) pin to GND. The KPD_PWR_N signal is not part of the keypad
matrix. The power key is only connected to the PM. This means that when the power key is pressed, an
interrupt will be generated to the MSM in order to power on the MCU. The MCU reads the QSC6020's interrupt
register and notifies that it is a KPD_PWR_N interrupt. The MCU reads the status of the KPD_PWR_N signal using
the control bus. If the KPD_PWR_N signal stays low for a certain time, the MCU accepts this as a valid power-on
state and continues with the software baseband initialization. If the power key does not indicate a valid
power-on situation, the MCU powers off the baseband.
Charger
Charging is controlled by start-up charging circuitry in order to detect and start charging in cases the main
battery is empty and the PM has no supply.
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