mc9s08gt32a Freescale Semiconductor, Inc, mc9s08gt32a Datasheet - Page 119

• Manufacturer Part Number: mc9s08gt32a
• Description: Hcs08 Microcontrollers 8-bit Microcontroller Family
• Manufacturer: Freescale Semiconductor, Inc

7.4.4
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)
ICGC2 = $31 (%00110001)
ICGS1 = $xx
ICGS2 = $xx
ICGFLTLU/L = $xx
ICGTRM = $xx
Freescale Semiconductor
Bit 7
Bit 6
Bit 5
Bits 4:3 CLKS
Bit 2
Bit 1
Bit 0
Bit 7
Bit 6:4 MFD
Bit 3
Bit 2:0 RFD
This is read only except for clearing interrupt flag
This is read only; good idea to read this before performing time critical operations
Not used in this example
Bit 7:0 TRIM
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
LOLRE
LOCRE
f
ICGOUT
0
0
1
01
0
0
0
011 Sets the MFD multiplication factor to 10
0
001 Sets the RFD division factor to ÷2
= (f
Configures oscillator for low-power operation
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 in stop modes
Loss-of-clock detection enabled
Unimplemented or reserved, always reads zero
Generates an interrupt request on loss of lock
Generates an interrupt request on loss of clock
Only need to write when trimming internal oscillator; done in separate
operation (see example #4)
IRG
MC9S08GB60A Data Sheet, Rev. 1.02
/ 7) * P * N / R ; P = 64, f
IRG
= 243 kHz
Bus
).
Initialization/Application Information
Eqn. 7-5
Eqn. 7-6
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