mc9s08gt32a Freescale Semiconductor, Inc, mc9s08gt32a Datasheet - Page 117

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

Figure 7-8
7.4.3
In this example, the FLL will be used (in FEE mode) to multiply the external 4 MHz oscillator up to
40-MHz to achieve 20 MHz bus frequency.
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
During reset initialization software, the clock scheme will be set to FLL engaged, external (FEE). So
Solving for N / R gives:
The values needed in each register to set up the desired operation are:
ICGC1 = $78 (%01111000)
Freescale Semiconductor
Bit 7
Bit 6
Bit 5
Bits 4:3 CLKS
Bit 2
Bit 1
Bit 0
RESET, STIO1, STOP2
shows flow charts for three conditions requiring ICG initialization.
Example #2: External Crystal = 4 MHz, Bus Frequency = 20 MHz
FLL LOCK STATUS.
RECOVERY FROM
HGO
RANGE
REFS
OSCSTEN 0
LOCD
INITIALIZE ICG
ICG1 = $38
ICG2 = $00
CONTINUE
LOCK = 1?
CHECK
N / R = 40 MHz /(4 MHz * 1) = 10 ; We can choose N = 10 and R = 1
YES
0
1
1
11
0
0
f
ICGOUT
NO
Figure 7-8. ICG Initialization for FEE in Example #1
Configures oscillator for low-power operation
Configures oscillator for high-frequency range; FLL prescale factor is 1
Requests an oscillator
FLL engaged, external reference clock mode
Disables the oscillator in stop modes
Loss-of-clock detection enabled
Unimplemented or reserved, always reads zero
= f
QUICK RECOVERY FROM STOP
ext
MC9S08GB60A Data Sheet, Rev. 1.02
RECOVERY FROM STOP3
* P * N / R ; P = 1, f
FLL LOCK STATUS.
OSCSTEN = 1
CONTINUE
LOCK = 1?
CHECK
YES
NOTE: THIS WILL REQUIRE THE OSCILLATOR TO START AND
STABILIZE. ACTUAL TIME IS DEPENDENT ON CRYSTAL /RESONATOR
AND EXTERNAL CIRCUITRY.
NO
ext
= 4.00 MHz
MINIMUM CURRENT DRAW IN STOP
RECOVERY FROM STOP3
Bus
FLL LOCK STATUS.
OSCSTEN = 0
).
CONTINUE
LOCK = 1?
CHECK
Initialization/Application Information
YES
NO
Eqn. 7-3
Eqn. 7-4
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