Freescale Semiconductor FlexRay MFR4310, Reference Manual

Page: 236 / 268

Oscillator (OSCV2)
MFR4310 Reference Manual, Rev. 2
236 Freescale Semiconductor
is the output of the crystal oscillator amplifier. All internal system clocks are derived from the EXTAL
input frequency.
NOTE
Freescale Semiconductor recommends an evaluation of the application
board and chosen resonator or crystal by the resonator or crystal supplier
.
The Crystal circuit is changed from standard.
The Pierce circuit is not suited for overtone resonators and crystals without
a careful component selection.
For more information, see the EXTAL pin description in Chapter 2.
7.3 Memory Map and Register Definition
The CRG contains the registers and associated bits for controlling and monitoring the OSCV2 module.
7.4 Functional Description
The OSCV2 block has two external pins, EXTAL and XTAL. The oscillator input pin, EXTAL, is intended
to be connected to a crystal or an external clock source. The XTAL pin is an output signal that provides
crystal circuit feedback.
A buffered EXTAL signal, OSCCLK, becomes the internal reference clock. To improve noise immunity,
the oscillator is powered by the V
DDOSC
and V
SSOSC
power supply pins.
7.4.1 Clock Monitor (CM)
The clock monitor circuit is based on an internal resistor-capacitor (RC) time delay so that it can operate
without a clock. If no OSCCLK edges are detected within this RC time delay, the clock monitor indicates
a failure which asserts self clock mode or generates a system reset depending on the state of the SCME bit.
If the clock monitor is disabled or the presence of clocks is detected, no failure is indicated. The clock
monitor function is enabled/disabled by the CME control bit, described in
Chapter 6, “Clocks and Reset
Generator (CRG) ”.
7.5 Resets
OSCV2 contains a clock monitor, which can trigger a reset. The control bits and status bits for the clock
monitor are described in
Chapter 6, “Clocks and Reset Generator (CRG) ”.