Clock Block Diagram For Crystal Operation; Mc68340 Crystal Oscillator - Motorola MC68340 User Manual

using crystal mode, the system clock frequency is programmable (using the W, X, and Y
bits in the SYNCR) over the range specified in Section 11 Electrical Characteristics
(see Table 4-2.).
20 pF
20 M
EXTAL XTAL
CRYSTAL
OSCILLATOR
NOTE 1: Must be low-leakage capacitor.
Figure 4-4. Clock Block Diagram for Crystal Operation
A separate power pin (V
the device powered down and to provide increased noise immunity for the clock circuits.
The source for V
CCSYN
capacitors placed as close as possible to the V
frequency. Figure 4-4 shows typical values for the bypass and PLL external capacitors.
The crystal manufacturer's documentation should be consulted for specific
recommendations for external components.
4-10
Freescale Semiconductor, Inc.
20 pF
XFC PIN
LOW-PASS
PHASE
FILTER
COMPARATOR
64
MUX
1
MODULUS
DIVIDER
0
SEL
6
0
$3F
Y
W
EXTAL
Figure 4-5. MC68340 Crystal Oscillator
) is used to allow the clock circuits to run with the rest of
CCSYN
should be a quiet power supply with adequate external bypass
MC68340 USER'S MANUAL
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V DDSYN
1
XFC 0.1 F
0.1 F
V DDSYN
0.01 F
VCO
2
4
8
FEEDBACK DIVIDER
60 k
XTAL
60 k
.
pin to ensure a stable operating
CCSYN
MUX
1
CLKOUT
0
SEL
0
X
MOTOROLA