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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.
EXTAL
XTAL
Figure 19.2 Connection of Crystal Resonator (Example)
Table 19.1 Damping Resistance Value
Damping
Frequency f (MHz)
Resistance
2 < f ≤ ≤ ≤ ≤ 4 4 < f ≤ ≤ ≤ ≤ 8 8 < f ≤ ≤ ≤ ≤ 10 10 < f ≤ ≤ ≤ ≤ 13 13 < f ≤ ≤ ≤ ≤ 16 16 < f ≤ ≤ ≤ ≤ 18 18 < f ≤ ≤ ≤ ≤ 20
Value
2
Rd (Ω)
1 k
500
Note: A crystal resonator between 2 MHz and 20 MHz 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.)
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.
C
L1
Rd
C
L2
200
0
0
Section 19 Clock Pulse Generator
C
= C
= 10 pF to 22 pF
L1
L2
0
0
Rev. 4.00 Jan 26, 2006 page 667 of 938
0
REJ09B0276-0400
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