Typewriter User Manual

4- 10 MC68340 USER’S MANUAL MOTOROLA
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.).
EXTAL
PHASE
C
OMPARATO
R
LOW-PASS
FILTER
VCO
CRYSTAL
O
SCILLATO
R
XTAL
XFC PIN
V
DDSYN
XFC
V
DDSYN
0.1
µ
F
0.01
µ
F
0.1
µ
F
NOTE 1: Must be low-leakage capacitor.
20 pF
20 pF
20 M
330 K
1
÷
4
MODULUS
DIVIDER
Y
W
FEEDBACK DIVIDER
0
1
SEL
MUX
0
$3F
÷
64
÷
8
6
SEL
0
1
MUX
÷
2
0
X
CLKOUT
Figure 4-4. Clock Block Diagram for Crystal Operation
.
XTAL
E
XTAL
60 kΩ
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.
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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