MC68340AB16E Datasheet, PDF (107/441 Pages) Motorola, Inc – Integrated Processor with DMA User’s Manual

Freescale Semiconductor, Inc.
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
EXTAL
20 pF
20 M
XTAL
XFC PIN
VDDSYN
XFC ¹
0.1 µF
0.1 µF
V _DDSYN
0.01 µF
CRYSTAL
OSCILLATOR
PHASE
COMPARATOR
÷64
MODULUS
DIVIDER
6
$3F
Y
LOW-PASS
FILTER
VCO
MUX
1
MUX
1
÷4
÷2
0
SEL
0
0
÷8
X
SEL
0
FEEDBACK DIVIDER
W
CLKOUT
NOTE 1: Must be low-leakage capacitor.
Figure 4-4. Clock Block Diagram for Crystal Operation
60 kΩ
EXTAL
XTAL
.60 kΩ
Figure 4-5. MC68340 Crystal Oscillator
A separate power pin (V_CCSYN) is used to allow the clock circuits to run with the rest of
the device powered down and to provide increased noise immunity for the clock circuits.
The source for V_CCSYN should be a quiet power supply with adequate external bypass
capacitors placed as close as possible to the V_CCSYN pin to ensure a stable operating
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
MC68340 USER’S MANUAL
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