sc9s08mz16 Freescale Semiconductor, Inc, sc9s08mz16 Datasheet - Page 143

• Manufacturer Part Number: sc9s08mz16
• Description: Hcs08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

8.6.4
In this example, the FLL will be used (in FEI mode) to multiply the internal 243 kHz (approximate)
reference clock up to 10.8 MHz to achieve 5.4 MHz bus frequency. This system will also use the trim
function to fine tune the frequency based on an external reference signal.
After the MCU is released from reset, the ICG is in self-clocked mode (SCM) and supplies approximately
8 MHz on ICGOUT which corresponds to a 4 MHz bus frequency (f
The clock scheme will be FLL engaged, internal (FEI). So
Solving for N / R gives:
A trim procedure will be required to hone the frequency to exactly 5.4 MHz. An example of the trim
procedure is shown in example #4.
The values needed in each register to set up the desired operation are:
ICGC1 = $28 (%00101000)
Freescale Semiconductor
Bit 7
Bit 6
Bit 5
Bits 4:3 CLKS
Bit 2
Bit 1
Example #3: No External Crystal Connection, 5.4 MHz Bus
Frequency
N / R = 10.8 MHz /(243/7 kHz * 64) = 4.86; We can choose N = 10 and R = 2.
HGO
RANGE
REFS
OSCSTEN 0
LOCD
Figure 8-14. ICG Initialization and Stop Recovery for Example #2
f
ICGOUT
0
0
1
01
0
FLL LOCK STATUS
INITIALIZE ICG
ICGC1 = $7A
ICGC2 = $30
= (f
Configures oscillator for low power
Configures oscillator for low-frequency range; FLL prescale factor is 64
Oscillator using crystal or resonator requested (bit is really a don’t care)
FLL engaged, internal reference clock mode
Disables the oscillator
Loss-of-clock enabled
CONTINUE
LOCK = 1?
RESET
CHECK
IRG
SC9S08MZ16 MCU Data Sheet, Rev. 1
YES
/ 7) * P * N / R; P = 64, f
NO
SOURCE (f
SERVICE INTERRUPT
FLL LOCK STATUS
FROM STOP
RECOVERY
CONTINUE
IRG
LOCK = 1?
CHECK
Bus
= 243 kHz
YES
= 4 MHz)
Bus
).
NO
Internal Clock Generator (S08ICGV4)
Eqn. 8-5
Eqn. 8-6
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