Datasheet

I/O Signals
MC68HC908GZ16 • MC68HC908GZ8 Data Sheet, Rev. 4
Freescale Semiconductor 67
4.4 I/O Signals
The following paragraphs describe the CGM I/O signals.
4.4.1 Crystal Amplifier Input Pin (OSC1)
The OSC1 pin is an input to the crystal oscillator amplifier.
4.4.2 Crystal Amplifier Output Pin (OSC2)
The OSC2 pin is the output of the crystal oscillator inverting amplifier.
4.4.3 External Filter Capacitor Pin (CGMXFC)
The CGMXFC pin is required by the loop filter to filter out phase corrections. An external filter network is
connected to this pin. (See Figure 4-2.)
NOTE
To prevent noise problems, the filter network should be placed as close to
the CGMXFC pin as possible, with minimum routing distances and no
routing of other signals across the network.
4.4.4 PLL Analog Power Pin (V
DDA
)
V
DDA
is a power pin used by the analog portions of the PLL. Connect the V
DDA
pin to the same voltage
potential as the V
DD
pin.
NOTE
Route V
DDA
carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
4.4.5 PLL Analog Ground Pin (V
SSA
)
V
SSA
is a ground pin used by the analog portions of the PLL. Connect the V
SSA
pin to the same voltage
potential as the V
SS
pin.
NOTE
Route V
SSA
carefully for maximum noise immunity and place bypass
capacitors as close as possible to the package.
4.4.6 Oscillator Enable Signal (SIMOSCEN)
The SIMOSCEN signal comes from the system integration module (SIM) and enables the oscillator and
PLL.
4.4.7 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.