83
4.3
Subclock Generator
Connecting a 32.768-kHz Crystal Oscillator: Clock pulses can be supplied to the subclock
divider by connecting a 32.768-kHz crystal oscillator, as shown in figure 4.7. Follow the same
precautions as noted in 4.2, Notes on Board Design.
X
X
C
1
C
2
1
2
C = C = 15 pF (typ.)
R
f
= 10 M
Ω
(typ.)
1
2
R
f
Figure 4.7 Typical Connection to 32.768-kHz Crystal Oscillator
Figure 4.8 shows the equivalent circuit of the 32.768-kHz crystal oscillator.
C
S
C
0
L
R
S
X
1
X
2
C = 1.5 pF typ
R = 14 k typ
f = 32.768 kHz
Crystal oscillator: MX38T
(Nihon Denpa Kogyo)
0
S
W
Ω
S
Figure 4.8 Equivalent Circuit of 32.768-kHz Crystal Oscillator
Pin Connection when Not Using Subclock: When the subclock is not used, connect pin X
1
to
V
CC
and leave pin X
2
open, as shown in figure 4.9.
X
X
1
2
V
CC
Open
Figure 4.9 Pin Connection when not Using Subclock