Motorola MC68HC908AB32 User Manual

Clock Generator Module (CGM)
Functional Description
MC68HC908AB32 — Rev. 1.0 Technical Data
MOTOROLA Clock Generator Module (CGM) 133
9.4 Functional Description
The CGM consists of three major sub-modules:
• Crystal oscillator circuit which generates the constant crystal
frequency clock, CGMXCLK.
• Phase-locked loop (PLL) which generates the programmable
VCO frequency clock CGMVCLK.
• Base clock selector circuit; this software-controlled circuit selects
either CGMXCLK divided by two or the VCO clock CGMVCLK
divided by two, as the base clock CGMOUT. The SIM derives the
system clocks from CGMOUT.
Figure 9-1 shows the structure of the CGM.
Figure 9-1. CGM Block Diagram
BCS
PHASE
DETECTOR
LOOP
FILTER
FREQUENCY
DIVIDER
VOLTAGE
CONTROLLED
OSCILLATOR
BANDWIDTH
CONTROL
LOCK
DETECTOR
CLOCK
CGMXCLK
CGMOUT
CGMVDV CGMVCLK
SIMOSCEN
CRYSTAL OSCILLATOR
INTERRUPT
CONTROL
CGMINT
CGMRDV
PLL ANALOG
÷2
CGMRCLK
SELECT
CIRCUIT
LOCK AUTO ACQ
VRS[7:4]
PLLIE PLLF
MUL[7:4]
TO SIM, SCI
TO SIM
MONITOR MODE
A
B
S*
USER MODE
*When S = 1, CGMOUT = B
OSC1
OSC2
V
DDA
CGMXFC V
SS
PTC3

Motorola MC68HC908AB32 Specifications

General

Brand	Motorola
Model	MC68HC908AB32
Category	Controller
Language	English