Oscillator Startup; Oscillator Stable; External Clock Mode; Osc Module Modes - NXP Semiconductors freescale KV4 Series Reference Manual

Table of Contents

Chapter 29 Oscillator (OSC)

29.8.1.2 Oscillator startup

The OSC enters startup state when it is configured to generate clocks (internally the

OSC_EN transitions high) using the internal oscillator circuits by setting the external

reference clock selection bit. In this state, the OSC module is enabled and oscillations are

starting up, but have not yet stabilized. When the oscillation amplitude becomes large

enough to pass through the input buffer, XTL_CLK begins clocking the counter. When

the counter reaches 4096 cycles of XTL_CLK, the oscillator is considered stable and

XTL_CLK is passed to the output clock OSC_CLK_OUT.

The OSC enters stable state when it is configured to generate clocks (internally the

OSC_EN transitions high) using the internal oscillator circuits by setting the external

reference clock selection bit and the counter reaches 4096 cycles of XTL_CLK (when

CNT_DONE_4096 is high). In this state, the OSC module is producing a stable output

clock on OSC_CLK_OUT. Its frequency is determined by the external components being

The OSC enters external clock state when it is enabled and external reference clock

selection bit is cleared. For details regarding external reference clock source in this MCU,

see the chip configuration details. In this state, the OSC module is set to buffer (with

hysteresis) a clock from EXTAL onto the OSC_CLK_OUT. Its frequency is determined

by the external clock being supplied.

The OSC is a pierce-type oscillator that supports external crystals or resonators operating

over the frequency ranges shown in

29-6. These modes assume the following

conditions: OSC is enabled to generate clocks (OSC_EN=1), configured to generate

clocks internally (MCG_C2[EREFS] = 1), and some or one of the other peripherals

(MCG, Timer, and so on) is configured to use the oscillator output clock

(OSC_CLK_OUT).

Table 29-6. Oscillator modes

Frequency Range

Low-frequency, high-gain

(32.768 kHz) up to f

(39.0625 kHz)

Table continues on the next page...

KV4x Reference Manual, Rev. 2, 02/2015

Freescale Semiconductor, Inc.