NXP Semiconductors MC9S08QL4, Reference Manual

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Chapter 1 Device Overview
MC9S08QL8 MCU Series Reference Manual, Rev. 1
16 NXP Semiconductors
The ICS supplies the following clock sources:
• ICSOUT — This clock source is used as the CPU clock and is divided by 2 to generate the
peripheral bus clock, BUSCLK. Control bits in the ICS control registers determine which of three
clock sources is connected:
— Internal reference clock
— External reference clock
— Frequency-locked loop (FLL) output
See
Chapter 11, Internal Clock Source (S08ICSV3) for details on configuring the ICSOUT clock.
• ICSLCLK — This clock source is derived from the digitally controlled oscillator, DCO, of the ICS
when the ICS is configured to run off of the internal or external reference clock. Development tools
can select this internal self-clocked source (~ 8 MHz) to speed up BDC communications in systems
where the bus clock is slow.
• ICSERCLK — This is the external reference clock and can be selected as the alternate clock for
the ADC module.
Section 11.4.7, External Reference Clock explains the ICSERCLK in more
detail. See Chapter 10, Analog-to-Digital Converter (S08ADC12V1) for more information
regarding the use of ICSERCLK with these modules.
• ICSIRCLK — This is the internal reference clock and can be selected as the real-time counter clock
source.
Chapter 11, Internal Clock Source (S08ICSV3) explains the ICSIRCLK in more detail. See
Chapter 13, Real-Time Counter (S08RTCV1) for more information regarding the use of
ICSIRCLK.
• ICSFFCLK — This generates the fixed frequency clock (FFCLK) after being synchronized to the
bus clock. It can be selected as clock source for the TPM module and MTIM module. The
frequency of the ICSFFCLK is determined by the settings of the ICS. See
Section 11.4.8, Fixed
Frequency Clock in Chapter 11, Internal Clock Source (S08ICSV3) for details.
• LPOCLK — This clock is generated from an internal low power oscillator that is completely
independent of the ICS module. The LPOCLK can be selected as the clock source to the RTC or
COP modules. See
Chapter 13, Real-Time Counter (S08RTCV1) and Section 5.4, Computer
Operating Properly (COP) Watchdog for details on using the LPOCLK with these modules.
• OSCOUT — This is the output of the XOSCVLP module and can be selected as the real-time
counter clock source.
• TCLK — TCLK is the optional external clock source for the TPM and MTIM modules. The TCLK
must be limited to 1/4th the frequency of the bus clock for synchronization. See
Chapter 15,
Timer/Pulse-Width Modulator (S08TPMV3) and Chapter 12, Modulo Timer (S08MTIMV1) for
more details.