M68ICS08GR datasheet(113/408 Pages) FREESCALE

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Clock Generator Module (CGMC)

I/O Signals

MC68HC908GR8 — Rev 4.0

Technical Data

MOTOROLA

Clock Generator Module (CGMC)

113

7.5.6 Oscillator Enable Signal (SIMOSCEN)

The SIMOSCEN signal comes from the system integration module (SIM)

and enables the oscillator and PLL.

7.5.7 Oscillator Stop Mode Enable Bit (OSCSTOPENB)

OSCSTOPENB is a bit in the CONFIG register that enables the oscillator

to continue operating during stop mode. If this bit is set, the Oscillator

continues running during stop mode. If this bit is not set (default), the

oscillator is controlled by the SIMOSCEN signal which will disable the

oscillator during stop mode.

7.5.8 Crystal Output Frequency Signal (CGMXCLK)

CGMXCLK is the crystal oscillator output signal. It runs at the full speed

of the crystal (fXCLK) and comes directly from the crystal oscillator circuit.

Figure 7-2 shows only the logical relation of CGMXCLK to OSC1 and

OSC2 and may not represent the actual circuitry. The duty cycle of

CGMXCLK is unknown and may depend on the crystal and other

external factors. Also, the frequency and amplitude of CGMXCLK can be

unstable at startup.

7.5.9 CGMC Base Clock Output (CGMOUT)

CGMOUT is the clock output of the CGMC. This signal goes to the SIM,

which generates the MCU clocks. CGMOUT is a 50 percent duty cycle

clock running at twice the bus frequency. CGMOUT is software

programmable to be either the oscillator output, CGMXCLK, divided by

two or the VCO clock, CGMVCLK, divided by two.

7.5.10 CGMC CPU Interrupt (CGMINT)

CGMINT is the interrupt signal generated by the PLL lock detector.

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