Power Key And System Power-Up; Modes Of Operation; Clocking Scheme - Nokia RM-627 Service Manual

RM-627
System Module

Power key and system power-up

When the battery is placed in the phone, the power key circuits are energized. When the power key is pressed,
the system boots up (if an adequate battery voltage is present).
Power down can be initiated by pressing the power key again and the system is powered down with the aid
of SW. The power key is connected to EM ASIC (N2200) via the PWRONX signal.

Modes of operation

Mode
NO_SUPPLY (Dead) mode means that the main battery is not present or its voltage is too low (below
EM ASIC master reset threshold) and that the back-up battery voltage is too low.
BACK_UP The main battery is not present or its voltage is too low but back-up battery voltage is
adequate and the 32 kHz oscillator is running (RTC is on).
PWR_OFF In this mode (warm), the main battery is present and its voltage is over EM ASIC master
reset threshold. All regulators are disabled, PurX is on low state, the RTC is on and the
oscillator is on. PWR_OFF (cold) mode is almost the same as PWR_OFF (warm), but the
RTC and the oscillator are off.
RESET RESET mode is a synonym for start-up sequence. RESET mode uses 32kHz clock to count
the REST mode delay (typically 16ms).
SLEEP SLEEP mode is entered only from PWR_ON mode with the aid of SW when the system's
activity is low.
FLASHING FLASHING mode is for SW downloading.

Clocking scheme

In BB5.44, two main clocks are provided to the system: 38.4MHz RF clock produced by VCTCXO in the RF section
and 32.768kHz sleep clock produced by EM ASIC N2200 with an external crystal.
32 k Sleep Clock is always powered on after startup. Sleep clock is used by RAPU for low-power operation.
SMPS Clk is 2.4MHz clock line from RAPU to EM ASIC N2200. In deep sleep mode, when VCTCXO is off, this signal
is set to '0'-state.
CLK600. The clock source is an internal RC oscillator in EM ASIC N2200 (during the power-up sequence) or
RAPU SMPS Clk.
Bluetooth has a separate 38.4MHz TCXO clock oscillator.
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