mc9s12xs128 Freescale Semiconductor, Inc, mc9s12xs128 Datasheet - Page 268

• Manufacturer Part Number: mc9s12xs128
• Description: Hcs12 Microcontrollers 16-bit Automotive Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Pierce Oscillator (S12XOSCLCPV2)
9.3
The CRG contains the registers and associated bits for controlling and monitoring the oscillator module.
9.4
The XOSC module has control circuitry to maintain the crystal oscillator circuit voltage level to an optimal
level which is determined by the amount of hysteresis being used and the maximum oscillation range.
The oscillator block has two external pins, EXTAL and XTAL. The oscillator input pin, EXTAL, is
intended to be connected to either a crystal or an external clock source. The XTAL pin is an output signal
that provides crystal circuit feedback.
A buffered EXTAL signal becomes the internal clock. To improve noise immunity, the oscillator is
powered by the VDDPLL and VSSPLL power supply pins.
9.4.1
In LCP mode a closed loop control system will be utilized whereby the amplifier is modulated to keep the
output waveform sinusoidal and to limit the oscillation amplitude. The output peak to peak voltage will be
kept above twice the maximum hysteresis level of the input buffer. Electrical specification details are
provided in the Electrical Characteristics appendix.
9.4.2
The clock monitor circuit is based on an internal RC time delay so that it can operate without any MCU
clocks. If no OSCCLK edges are detected within this RC time delay, the clock monitor indicates failure
which asserts self-clock mode or generates a system reset depending on the state of 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 the CRG block description chapter.
9.4.3
During wait mode, XOSC is not impacted.
9.4.4
XOSC is placed in a static state when the part is in stop mode except when pseudo-stop mode is enabled.
During pseudo-stop mode, XOSC is not impacted.
268
Memory Map and Register Definition
Functional Description
Gain Control
Clock Monitor
Wait Mode Operation
Stop Mode Operation
S12XS Family Reference Manual, Rev. 1.10
Freescale Semiconductor