MC68HC908GZ60 Datasheet, PDF (82/352 Pages) Freescale Semiconductor, Inc – Microcontrollers

Clock Generator Module (CGM)
4.4.8 Crystal Output Frequency Signal (CGMXCLK)
CGMXCLK is the crystal oscillator output signal. It runs at the full speed of the crystal (f_XCLK) and comes
directly from the crystal oscillator circuit. Figure 4-2 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 start up.
4.4.9 CGM Base Clock Output (CGMOUT)
CGMOUT is the clock output of the CGM. 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.
4.4.10 CGM CPU Interrupt (CGMINT)
CGMINT is the interrupt signal generated by the PLL lock detector.
4.5 CGM Registers
These registers control and monitor operation of the CGM:
• PLL control register (PCTL)
(See 4.5.1 PLL Control Register.)
• PLL bandwidth control register (PBWC)
(See 4.5.2 PLL Bandwidth Control Register.)
• PLL multiplier select register high (PMSH)
(See 4.5.3 PLL Multiplier Select Register High.)
• PLL multiplier select register low (PMSL)
(See 4.5.4 PLL Multiplier Select Register Low.)
• PLL VCO range select register (PMRS)
(See 4.5.5 PLL VCO Range Select Register.)
Figure 4-3 is a summary of the CGM registers.
Addr.
$0036
$0037
$0038
Register Name
PLL Control Register ^Read:
(PCTL) Write:
See page 83. _Reset:
PLL Bandwidth Control ^Read:
Register (PBWC) Write:
See page 85. _Reset:
PLL Multiplier Select High ^Read:
Register (PMSH) Write:
See page 86. _Reset:
Bit 7
PLLIE
0
AUTO
0
0
0
6
PLLF
0
LOCK
0
0
5
PLLON
1
ACQ
0
0
0
0
= Unimplemented
4
3
BCS
R
0
0
0
0
0
0
0
MUL11
0
0
R = Reserved
Figure 4-3. CGM I/O Register Summary
2
R
0
0
0
MUL10
0
1
VPR1
0
0
0
MUL9
0
Bit 0
VPR0
0
R
0
MUL8
0
MC68HC908GZ60 • MC68HC908GZ48 • MC68HC908GZ32 Data Sheet, Rev. 6
82
Freescale Semiconductor