Hardware manual

Rev. 3.0, 09/98, page 78 of 361
5.2 Oscillator Circuit
If an external crystal is connected across the EXTAL and XTAL pins, the on-chip oscillator circuit
generates a clock signal for the system clock divider. Alternatively, an external clock signal can
be applied to the EXTAL pin.
(1) Connecting an External Crystal
①① Circuit Configuration: An external crystal can be connected as in the example in figure 5.2.
An AT-cut parallel resonating crystal should be used.
EXTAL
XTAL
C
L1
C L1 = C L2 = 10 to 22pF
C
L2
Figure 5.2 Connection of Crystal Oscillator (Example)
②② Crystal Oscillator: The external crystal should have the characteristics listed in table 5.1.
Table 5.1 External Crystal Parameters
Frequency (MHz) 2 4 8 12 16 20
Rs max (Ω) 500 120 60 40 30 20
C0 (pF) 7 pF max
C L
C 0
XTAL EXTAL
LR
S
AT-cut parallel resonating crystal
Figure 5.3 Equivalent Circuit of External Crystal