19.2 Oscillator Circuit
Clock pulses can be supplied by connecting a crystal resonator, or by input of an external clock
signal.
19.2.1 Connecting a Crystal Resonator
Circuit Configuration: A crystal resonator can be connected as in the example in figure 19-2.
The damping resistance Rd should be selected according to table 19-1. An AT-cut parallel-
resonance crystal should be used.
Figure 19-2 Connection of Crystal Resonator (Example)
Table 19-1 Damping Resistance Value
Damping Resistance
Frequency f (MHz)
Value
2
2
<
f
≤
4
4
<
f
≤
8
8
<
f
≤
10
10
<
f
≤
13 13
<
f
≤
16 16
<
f
≤
18
Rd
For products
1 k
500
200
0
0
0
0
(
Ω
)
listed below
*
HD64F3048
1 k
1 k
500
200
100
0
—
Note: A crystal resonator between 2 MHz and 18 MHz (between 2 MHz and 16 MHz for the flash
memory version) can be used. If the chip is to be operated at less than 2 MHz, the on-chip
frequency divider should be used. (A crystal resonator of less than 2 MHz cannot be used.)
*
HD6473048, HD6433048, HD6433047, HD6433045, HD6433044
Crystal Resonator: Figure 19-3 shows an equivalent circuit of the crystal resonator. The crystal
resonator should have the characteristics listed in table 19-2.
EXTAL
XTAL
C
L1
C
L2
C = C = 10 pF to 22 pF
L1 L2
Rd
634
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