
Oscillator Module (OSC)
Data Sheet
MC68HLC908QY/QT Family — Rev. 2
98
Oscillator Module (OSC)
MOTOROLA
For the internal oscillator configuration, the OSC1 pin can assume other functions
11.4.2 Crystal Amplifier Output Pin (OSC2/PTA4/BUSCLKX4)
For the XTAL oscillator device, the OSC2 pin is the crystal oscillator inverting
amplifier output.
For the external clock option, the OSC2 pin is dedicated to the PTA4 I/O function.
The OSC2EN bit has no effect.
For the internal oscillator or RC oscillator options, the OSC2 pin can assume other
of the oscillator clock (BUSCLKX4).
11.4.3 Oscillator Enable Signal (SIMOSCEN)
The SIMOSCEN signal comes from the system integration module (SIM) and
enables/disables either the XTAL oscillator circuit, the RC oscillator, or the internal
oscillator.
11.4.4 XTAL Oscillator Clock (XTALCLK)
XTALCLK is the XTAL oscillator output signal. It runs at the full speed of the crystal
(fXCLK) and comes directly from the crystal oscillator circuit. Figure 11-2 shows only the logical relation of XTALCLK to OSC1 and OSC2 and may not represent
the actual circuitry. The duty cycle of XTALCLK is unknown and may depend on
the crystal and other external factors. Also, the frequency and amplitude of
XTALCLK can be unstable at start up.
11.4.5 RC Oscillator Clock (RCCLK)
RCCLK is the RC oscillator output signal. Its frequency is directly proportional to
the time constant of external R and internal C. Figure 11-3 shows only the logical
relation of RCCLK to OSC1 and may not represent the actual circuitry.
Table 11-1. OSC2 Pin Function
Option
OSC2 Pin Function
XTAL oscillator
Inverting OSC1
External clock
PTA4 I/O
Internal oscillator
or
RC oscillator
Controlled by OSC2EN bit in PTAPUE register
OSC2EN = 0: PTA4 I/O
OSC2EN = 1: BUSCLKX4 output
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Freescale Semiconductor, Inc.
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