MC9S08JM16 Datasheet, PDF (22/386 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 1 Device Overview
The MCG supplies the following clock sources:
• MCGOUT — This clock source is used as the CPU, USB RAM and USB module clock, and is
divided by two to generate the peripheral bus clock (BUSCLK). Control bits in the MCG control
registers determine which of the three clock sources is connected:
— Internal reference clock
— External reference clock
— Frequency-locked loop (FLL) or phase-locked loop (PLL) output
See Chapter 12, “Multi-Purpose Clock Generator (S08MCGV1),” for details on configuring the
MCGOUT clock.
• MCGLCLK — This clock source is derived from the digitally controlled oscillator (DCO) of the
MCG. Development tools can select this internal self-clocked source to speed up BDC
communications in systems where the bus clock is slow.
• MCGIRCLK — This is the internal reference clock and can be selected as the real-time counter
(RTC) clock source. Chapter 12, “Multi-Purpose Clock Generator (S08MCGV1),” explains the
MCGIRCLK in more detail. See Chapter 13, “Real-Time Counter (S08RTCV1),” for more
information regarding the use of MCGIRCLK.
• MCGERCLK — This is the external reference clock and can be selected as the clock source of
RTC and ADC module. Section 12.4.6, “External Reference Clock,” explains the MCGERCLK in
more detail. See Chapter 13, “Real-Time Counter (S08RTCV1),” and Chapter 10,
“Analog-to-Digital Converter (S08ADC12V1),” for more information regarding the use of
MCGERCLK with these modules.
• MCGFFCLK — This clock source is divided by two to generate FFCLK after being synchronized
to the BUSCLK. It can be selected as clock source for the TPM modules. The frequency of the
MCGFFCLK is determined by the settings of the MCG. See the Section 12.4.7, “Fixed Frequency
Clock,” for details.
• LPO clock— This clock is generated from an internal low power oscillator that is completely
independent of the MCG module. The LPO clock 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 LPO clock with these modules.
• TPMCLK — TPMCLK is the optional external clock source for the TPM modules. The TPMCLK
must be limited to 1/4th the frequency of the BUSCLK for synchronization. See Chapter 16,
“Timer/Pulse-Width Modulator (S08TPMV2),” for more details.
MC9S08JM16 Series Data Sheet, Rev. 2
22
Freescale Semiconductor