Oscillator (OSC)
5.3 Internal Oscillator
The internal oscillator clock (ICLK), with a frequency of f
, is a free running clock that requires no
ICLK
external components. It can be selected as the CGMXCLK for the CGM and MCU sub-systems; and the
OSCCLK clock for the TBM. The ICLK is also the reference clock input to the computer operating properly
(COP) module.
Due to the simplicity of the internal oscillator, it does not have the accuracy and stability of the RC
oscillator or the x-tal oscillator. Therefore, the ICLK is not suitable where an accurate bus clock is required
and it should not be used as the CGMRCLK to the CGM PLL.
The internal oscillator by default is always available and is free running after POR or reset. It can be
turned-off in stop mode by setting the STOP_ICLKDIS bit before executing the STOP instruction.
Figure 5-4 shows the logical representation of components of the internal oscillator circuitry.
From SIM
SIMOSCEN
From SIM
BUS CLOCK
To Clock Selection MUX
and COP
ICLK
CONFIG2
EN
INTERNAL OSCILLATOR
STOP_ICLKDIS
MCU
OSC2
Figure 5-4. Internal Oscillator
MC68HC908AP Family Data Sheet, Rev. 4
74
Freescale Semiconductor
FREESCALE [ Freescale ]
