MC9S08JM16CGTE FREESCALE [Freescale Semiconductor, Inc], MC9S08JM16CGTE Datasheet - Page 199

• Manufacturer Part Number: MC9S08JM16CGTE
• Description: Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

12.5.2.2
In this example, the MCG will move through the proper operational modes from PEE mode with a 4 MHz
crystal configured for an 8 MHz bus frequency (see previous example) to BLPI mode with a 16 kHz bus
frequency.First, the code sequence will be described. Then a flowchart will be included which illustrates
the sequence.
Freescale Semiconductor
1. First, PEE must transition to PBE mode:
2. Then, PBE must transition either directly to FBE mode or first through BLPE mode and then to
3. Next, FBE mode transitions into FBI mode:
a) MCGC1 = 0x90 (%10010000)
b) Loop until CLKST (bits 3 and 2) in MCGSC are %10, indicating that the external reference
FBE mode:
a) BLPE: If a transition through BLPE mode is desired, first set LP (bit 3) in MCGC2 to 1
b) BLPE/FBE: MCGC1 = 0xB8 (%10111000)
c) BLPE/FBE: MCGC3 = 0x04 (%00000100)
d) BLPE: If transitioning through BLPE mode, clear LP (bit 3) in MCGC2 to 0 here to switch to
e) FBE: Loop until PLLST (bit 5) in MCGSC is clear, indicating that the current source for the
f) FBE: Optionally, loop until LOCK (bit 6) in the MCGSC is set, indicating that the FLL has
a) MCGC1 = 0x44 (%01000100)
b) Loop until IREFST (bit 4) in MCGSC is 1, indicating the internal reference clock has been
c) Loop until CLKST (bits 3 and 2) in MCGSC are %01, indicating that the internal reference
– CLKS (bits 7 and 6) set to %10 in order to switch the system clock source to the external
clock is selected to feed MCGOUT
– RDIV (bits 5-3) set to %111, or divide-by-128 because 4 MHz / 128 = 31.25 kHz which is
– PLLS (bit 6) clear to 0 to select the FLL. In BLPE mode, changing this bit only prepares the
FBE mode
PLLS clock is the FLL
acquired lock. Although the FLL is bypassed in FBE mode, it is still enabled and running.
– CLKS (bits7 and 6) in MCGSC1 set to %01 in order to switch the system clock to the
– IREFS (bit 2) set to 1 to select the internal reference clock as the reference clock source
– RDIV (bits 5-3) set to %000, or divide-by-1 because the trimmed internal reference must be
selected as the reference clock source
clock is selected to feed MCGOUT
Example # 2: Moving from PEE to BLPI Mode: External Crystal = 4 MHz,
Bus Frequency =16 kHz
reference clock
in the 31.25 kHz to 39.0625 kHz range required by the FLL. In BLPE mode, the
configuration of the RDIV does not matter because both the FLL and PLL are disabled.
Changing them only sets up the dividers for FLL usage in FBE mode
MCG for FLL usage in FBE mode. With PLLS = 0, the VDIV value does not matter.
internal reference clock
within the 31.25 kHz to 39.0625 kHz range required by the FLL
MC9S08JM16 Series Data Sheet, Rev. 2
Multi-Purpose Clock Generator (S08MCGV1)
199