mc9s08qg4 Freescale Semiconductor, Inc, mc9s08qg4 Datasheet - Page 155

• Manufacturer Part Number: mc9s08qg4
• Description: Hcs08 Microcontrollers Microcontroller Family
• Manufacturer: Freescale Semiconductor, Inc

10.5.1.2
To change from FEE or FBE clock modes to FEI or FBI clock modes, follow this procedure:
Freescale Semiconductor
4. The CLKST bits can be monitored to determine when the mode switch has completed. If FEE was
1. If saved, copy the TRIM and FTRIM values from FLASH to the ICSTRM and ICSSC registers.
2. Enable the internal clock reference by selecting FBI (CLKS = 0:1) or selecting FEI (CLKS = 0:0,
3. Wait for the internal clock reference to stabilize. The typical startup time is given in the Electrical
4. Write to ICSC2 to disable the external clock.
5. The CLKST bits in the ICSSC register can be monitored to determine when the mode switch has
— If entering FEE, set the reference divider and clear the IREFS bit to switch to the external
— The internal reference can optionally be kept running by setting the IRCLKEN bit. This is
selected, the bus clock will be stable in t
switching from FEI to FEE.
This needs to be done only once after POR.
RDIV = 0:0:0, and IREFS = 1) in ICSC1.
Characteristics appendix.
— The external reference can optionally be kept running by setting the ERCLKEN bit. This is
— If FBI will be the selected mode, also set the LP bit at this time to minimize power
completed. The CLKST bits will not change when switching from FEE to FEI. If FEI was selected,
the bus clock will be stable in t
reference.
useful if the application will switch back and forth between internal clock and external clock
modes. For minimum power consumption, leave the internal reference disabled while in an
external clock mode.
useful if the application will switch back and forth between internal clock and external clock
modes. For minimum power consumption, leave the external reference disabled while in an
internal clock mode.
consumption.
Initialization Sequence, External Clock Mode to Internal Clock Mode
The internal reference must be enabled and running before disabling the
external clock. Therefore it is imperative to execute steps 2 and 3 before
step 4.
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 4
Acquire
milliseconds.
Acquire
NOTE
milliseconds. The CLKST bits will not change when
Chapter 10 Internal Clock Source (S08ICSV1)
155