Clocking Scheme - Nokia RM-51 Service Manual

RM-51
System module and user interface
Voltage limits
The voltage limits of the system are listed in the following table. These are also controlling system states.
Parameter
VMSTR+
VMSTR-
VCOFF+
VCOFF-
V_BUCOFF+
V_BUCOFF-
SWCOFF
The master reset threshold controls the internal reset of UEMEK. If battery voltage is above VMSTR, UEMEK's
charging control logic is alive. Also, RTC is active and supplied from the main battery. Above VMSTR UEMEK allows
the system to be powered on although this may not succeed due to voltage drops during start-up. SW can also
consider battery voltage too low for operation and power down the system.

Clocking scheme

A 26 MHz VCXO, voltage controlled crystal oscillator, is used as system clock generator in GSM. During the system
start-up, UEMEK RC-oscillators generate timing for state machines. All clock signals of the engine are illustrated
in following figure.
Bluetooth uses a 26 MHz clock.
FM radio uses 32.768 kHz, the SleepClk.
In SLEEP mode, the VCXO is off. UEMEK generates a low frequency clock signal, the sleep clock at 32.768 kHz, that
is fed to UPP_WD2, Bluetooth and ZOCUS.
9238460 (Issue 1)
Description
Master reset threshold (rising)
Master reset threshold (falling)
Hardware cutoff (rising)
Hardware cutoff (falling)
Back-up battery cutoff (rising)
Back-up battery cutoff (falling)
SW cutoff limit (> regulator drop-
out limit) MIN!
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Value
2.1 V (typ.)
1.9 V (typ.)
3.1 V (typ.)
2.8 V (typ.)
2.1 V (typ.)
2.0 V (typ.)
3.3 V SW changeable
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