Nokia 2608 Service Manual page 97

RM-376
System Module and User Interface
TCXO
The MSM device integrates a phase-locked loop from the TCXO clock input.
The PM optimizes TCXO operation that enables and disables appropriate circuits in the proper sequence. The
controller is enabled by the signal from the MSM. When the selected transition occurs at TCXO_EN, the
controller quickly enables the TCXO regulator and the input buffer, and begins counting SLEEP_CLK pulses.
Within an initial power on period, the TCXO will be stabilized to its own calibrated frequency. This initial period,
in units of 32.768 kHz clock pulses, is programmed into a timer within the controller. When the timer expires,
the output buffer is enabled. It synchronizes with the TCXO input such that the TCXO_OUT signal is glitch free,
only valid TCXO pulses are output.
Figure 9 TCXO Enable Timing Diagram
The input buffer (TCXO_IN) accepts sinusoidal or square wave signals at or near 19.2 MHz. The input buffer
(TCXO_IN) is powered from the TCXO regulator while the output buffer is powered by VREG_MSMP.
The regulator of TCXO is turned off after the TCXO_EN signal is removed. Upon power-up, the PM defaults to
this SBI-controlled mode with the TCXO defaulted on. This assures the MSM will always have a clock available
immediately at power-up even if TCXO_EN is low.
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